LEES 2021 Low Energy Electrodynamics in Solids - International Conference on - Research Services

LEES 2021
International Conference on
Low Energy
Electrodynamics in Solids
 June 28 - July 8, 2021

Table of Contents

 Code of Conduct .................................................................................................................................. 3

 Support Organizations........................................................................................................................4-6
 ..................................................................................................................... 4-6

 Program................................................................................................................................................7

 Abstracts............................................................................................................................................. 15

 • Monday, June 28........................................................................................................................... 15

 • Tuesday, June 29........................................................................................................................... 22

 • Wednesday, June 30..................................................................................................................... 30

 • Thursday, July 1............................................................................................................................. 36

 • Monday, July 5.............................................................................................................................. 42

 • Tuesday, July 6.............................................................................................................................. 50

 • Wednesday, July 7......................................................................................................................... 57

 • Thursday, July 8............................................................................................................................. 64

2

Code of Conduct

The organizers of the LEES 2020 conference are fully committed to it being an inclusive event, and as
organizers we will do everything in our power to make it a safe, productive, and welcoming space to all
attendees. All participants, including , but not limited to, attendees, speakers, volunteers, exhibitors, fac-
ulty, staff, students, service providers, and others are expected to abide by the LEES code of Conduct.

The mission of the LEES conference is to provide a forum for interdisciplinary research on low energy
electrodynamics in solids and in exotic condensed phases. The discussions generated may arouse debate
and strong disagreements may occur. Our goal is to encourage the discussion while maintaining respect
for others.

All participants are expected to:
• Treat each other with respect
• Communicate openly with respect, critiquing ideas rather then individuals
• Alert LEES organizers or staff if you see a dangerous situation or someone in distress

Unacceptable behavior includes but is not limited to:
• Harassment, intimidation, or discrimination of anyone in any form
• Verbal abuse in any form
• Unwelcome sexual advances or comments
• Intimidating or hostile comments or conduct

Consequences:
Anyone requested to stop unacceptable behavior is expected to comply immediately. LEES staff (or their
designee) or security/local police may take any action deemed necessary and appropriate, including im-
mediate removal from the meeting without warning or refund.

All unacceptable behavior should be reported to the conference chair (Kenneth S. Burch), Staff, (Andrea
Wherry) or members of the local organizing committee. Incidents may be reported via email or via the
chat function in zoom.

 3

Supported By

 Thank you to the companies and organizations that
 have made LEES possible.

4

Supported By

 TeraHertz

Modern Quality Control and Failure Analysis

  Quality Control
 Confirm the identity and quality of both
 raw materials as well as finished products.
 Also offers the possibility of examining
 coatings and layer thicknesses.

  Failure Analysis
 Determine the chemical reason behind
 product failure:
 Identify contaminations and detect
 wrong compositions.

  Surface Analysis
 Check technical cleanliness and analyze
 microscopic contaminants. Identify
 inclusions and pollutants to draw
 conclusions about the causes of failure.

  Reverse Engineering
 Investigate competitor´s products and
 obtain valuable information about the
 materials used.

Contact us for more details: www.bruker.com/optics
 Spectroscopy
Innovation with Integrity

 5

Supported By

 GigaHertz

 MegaHertz

6

Program - Monday, June 28
 *All times on the Program are Eastern Standard Time

 Novel Magnets
 Chair: Kamaras Katalin
10:00 AM Evan Constable Vibronic processes in the quantum spin ice candidate Tb2Ti2O7

10:30 AM Rolando Valdes Aguilar Magnetic dynamics of honeycomb antiferromagnets

11:00 AM Natalia Drichko Time reversal and lattice symmetry breaking in Nd2Ir2O7 observed by
 Raman scattering spectroscopy

11:20 AM Itzik Kapon Magnetic field tuning of the valley population in the Weyl semi-metal
 phase of Nd$_2$Ir$_2$O$_7$
11:40 AM Break
12:30 PM Poster Session 1
 Berend Zwartsenberg Spin-orbit coupling effects in Sr2IrO4
 Carina Belvin Revealing the soft electronic modes involved in magnetite’s Verwey
 transition
 Giorgio Sangiovanni Design and realization of topological Dirac fermions on a triangular lattice

 Kirill Amelin Experimental observation of E8 particles in Ising-chain compounds
 Martin Dressel Dielectric Catastrophe at the Mott Transition
 Nimi Bachar Unconventional free charge in the correlated Weyl semimetal Nd2Ir2O7
 Severino Adler From Mott to Dirac Fermions via Van der Waals Stacking
 Shiming Lei Magnetic skyrmions in non-Gd based centrosymmetric magnet
 Valentina Brosco Rashba-metal to Mott-insulator transition - spectral signatures
 Wibke Bronsch Time- and Angle-Resolved Photoemission Study on Bulk VSe2
 Yuanyuan Xu Importance of dynamic lattice effects for crystal field excitations in
 quantum spin ice candidate Pr2Zr2O7
2:00 PM Long Break
 New Results in Mott Systems
 Chair: Dmitri Basov
7:00 PM Jie Shan Electrons in 2D semiconductor moiré superlattices
7:30 PM Yiping Wang Modulation Doping via a 2D Crystalline Acceptor
8:00 PM Masahiro Sato Nonlinear Optical Responses in Quantum Spin Liquids
8:20 PM Shuqiu Wang Scattering Interference Signature of a Pair Density Wave State in the
 Cuprate Pseudogap Phase
8:40 PM Break

 7

Tuesday, June 29
 Novel Optics in 2D Materials
 Chair: Marc Scheffler
 10:00 AM Ingrid Barcelos Probing Polaritons in 2D Materials with Synchrotron Infrared
 Nanospectroscopy
 10:30 AM Hanan Herzig Sheinfux Bound in the continuum modes in indirectly-patterned hyperbolic media

 11:00 AM Jeremy Levy Gate-Tunable Optical Nonlinearities and Extinction in Graphene/LaAlO3/
 SrTiO3 Nanostructures
 11:30 AM Alexey Kuzmenko Infrared nanoscopy of polaritons in functional oxides and interfaces
 11:50 AM Break
 12:30 PM Poster Session 2
 Amalia Coldea Anomalous magnetotransport of the nematic FeSe and related
 chalcogenides
 Claudio Giannetti Non-thermal metallic phase emerging from nanoscale complexity in a
 photo-excited Mott material
 Daniele Nicoletti Radiating Stripes
 Ivan Fotev Ultrafast Pump-Probe Spectroscopy of BaFe2As2 under High Pressures
 Jean-Côme Philippe Orbital dichotomy of Fermi liquid properties in Sr2RuO4 probed by Raman
 spectroscopy
 Jonathan B. Curtis Spectroscopic signatures of time-reversal symmetry breaking
 superconductivity
 Marco Marciani Resistivity anisotropy in nematic FeSe from multiorbital Boltzmann
 equation
 Michele Buzzi Photo-molecular high temperature superconductivity
 Min-Cheol Lee Ultrafast strain modulation of superconductivity in cuprate
 heterostructures
 Roberta Citro Topological superconductivity by orbital confinement in oxide nanowires
 2:00 PM Long Break
 Unconventional Superconductivity 1
 Chair: Setsuko Tajima
 7:00 PM Johnpierre Paglione Exotic superconductivity in nearly ferromagnetic UTe2
 7:30 PM Peter D. Johnson Time Reversal Symmetry Breaking in the FeTe1-xSex family of high Tc
 superconductors
 8:00 PM Ryan Day The Three-Dimensional Electronic Structure of LiFeAs: Strong-coupling
 Superconductivity and Topology in the Iron Pnictides
 8:20 PM Masamichi Nakajima Effects of electronic correlations and nematicity in FeSe1-xTex studied by
 optical spectroscopy
 8:40 PM Break

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Wednesday, June 30
 Optics in Quantum Matter 1
 Chair: Andrea Perucchi
10:30 AM Tommaso Cea Plasmons, phonons and superconductivity in twisted bilayer graphene
11:00 AM Milan Orlita Suppressed Auger scattering and tunable light emission of Landau-
 quantized massless Kane electrons
11:20 AM Prineha Narang Predicting Correlated Light-Matter Interactions
11:50 AM Méasson Marie-Aude Collective mode of the Hidden Order State in URu2Si2: Degeneracy and
 Symmetry
12:10 PM Long Break
 Magnetic Topological Systems
 Chair: N. Peter Armitage
7:00 PM Ilya Sochnikov Microscopy of tunable magnetic domains in noncentrosymmetric
 ferromagnetic Weyl semimetal
7:30 PM Shingo Toyoda Nonreciprocal second harmonic generation in a magnetoelectric CuB2O4

7:50 PM Changyoung Kim Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-
 protected nodal structures in ferromagnetic perovskite oxide thin films

8:20 PM Artem Strashko Crescent states in charge-imbalanced polariton condensates
8:40 PM Break
9:00 PM Poster Session 3
 Changmin Lee Observation of a phase transition within the domain walls of the magnetic
 Weyl semimetal Co3Sn2S2
 Gael Grissonnanche T-linear resistivity from an isotropic Planckian scattering rate
 Jae Hoon Kim Terahertz Electrodynamics of Superconducting Nb Films in External
 Magnetic Field
 Kazuya Shinjo Effect of phase string on single-hole dynamics in the two-leg Hubbard
 ladder
 Ran Jing Terahertz response of monolayer and few-layer WTe_2 at the nanoscale
 Takahiro Ito Angle-resolved photoemission study of MAX phase compound Ti2SnC
 Yinming Shao Nonlinear Nano-electrodynamics of a Weyl semimetal
 Yue Sun Mapping Domain Wall Topology in the Magnetic Weyl Semimetal CeAlSi
10:30 PM Break/Poster Session Ends

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Thursday, July 1

 9:00 AM LEES 2022 Announcement
 9:20 AM Genzel Prize Ceremony
 9:30 AM Genzel Prize Invited Talk
 10:00 AM Break
 10:30 AM Poster Session 4
 Bastien Michon The spectral weight of hole doped cuprates across the pseudogap critical
 point.
 Erik van Heumen Disentangling carrier density and momentum relaxation in cuprate
 superconductors
 Fabio Boschini Non-monotonic electron interactions in the copper oxide plane
 Florence Observation of sub-gap superconducting modes with Kinetic Inductance
 Levy-Bertrand Detectors
 Francesco Barantani Temperature dependence of d-d excitons in hole-doped cuprates
 Francesco Gabriele Coupled plasma waves in layered cuprates
 Marco Grilli Strange metal behaviour from charge density fluctuations in cuprates
 Marta Zonno Ubiquitous suppression of the nodal coherent spectral weight in Bi-based
 cuprates
 Petr Adamus "Pseudogap in the c-axis (interplane) conductivity of a pair of
 t-J planes with a single doped hole"
 12:00 PM Long Break
 Novel Magnets 2
 Chair: Matteo Mitrano
 7:00 PM Xiao-Xiao Zhang Ultrafast spin dynamics in 2D antiferromagnet
 7:30 PM Md Mofazzel Hosen Anomalous Raman response of a Charge Density Wave in a high mobility,
 2D antiferromagnet
 7:50 PM Xiaodong Xu Intertwined Topological and Magnetic Orders in Atomically Thin Chern
 Magnet
 8:20 PM In-Sang Yang Spin Excitation in Hexagonal LuMnO3
 8:40 PM Break

10

Monday, July 5
 Unconventional Superconductivity 2
 Chair: Dmitrii Maslov
10:00 AM Nurit Avraham Visualization of Topological Boundary Modes Manifesting Topological
 Nodal-Point Superconductivity
10:30 AM Andrea Cavalleri Advances in Optically Driven Superconductivity
11:00 AM Denitsa Baykusheva Ultrafast renormalization of the onsite Coulomb repulsion in an
 underdoped cuprate
11:20 AM Stuart Brown Even parity superconducting state of the strongly correlated Fermi Liquid
 Sr2RuO4
11:50 AM Break
12:30 PM Poster Session 5
 Alexander Boris Approaching 2D Superconductivity in Ultrathin DyBa2Cu3O7-δ Films
 Fabian Mooshammer Ultrafast low-energy dynamics of excitons in twisted van der Waals bilayers
 Federico Cilento Decoupling electronic and lattice contributions to the unconventional
 charge-density-wave transition of NbSe2 by time-resolved optical
 spectroscopy
 Götz Seibold Third harmonics generation from collective modes in disordered
 superconductors
 Jan Gospodaric Energy spectrum of semi-metallic HgTe quantum wells
 Miguel-Ángel Sánchez- Optical signatures of multifold fermions in the chiral topological
 Martínez semimetals RhSi and CoSi
 Riccardo Arpaia Doping evolution of charge density fluctuations across the entire dome of
 high-Tc superconductors
 Rocco Vitalone Cryogenic THz Nano Imaging and Spectroscopy Graphene/RuCl3
 Heterostructures
 Grégory Setnikar Structural instability and superconducting state of V3Si: a Raman study
 Stefano Dal Conte Interlayer charge transfer and spin/valley dynamics in TMD
 heterostructures
2:00 PM Long Break
 Graphite, Graphene and Flat Bands
 Chair: Jason Hancock
7:00 PM MengXing Na Time-and Angle-Resolved Photoemission studies of electron-phonon
 coupling in graphite
7:30 PM Yaxian Wang Ab initio signatures of phonon-mediated hydrodynamic transport in
 semimetals
7:50 PM Bohm Jung Yang Wave function geometry and anomalous Landau levels of flat bands
8:20 PM Sandeep Joy Transparent mirror effect in twist-angle-disordered bilayer graphene
8:40 PM Break

 11

Tuesday, July 6
 Correlated States 1
 Chair: Dirk Van Der Marel
 10:00 AM Prachi Sharma Optical conductivity of Dirac Fermi liquid
 10:30 AM Fahad Mahmood Observation of a marginal Fermi glass using THz 2D coherent spectroscopy
 10:50 AM Elena Bascones Correlated states in graphene based moiré systems
 11:20 AM Sharareh Sayyad Pairing and non-Fermi liquid behavior in partially flat-band systems

 11:40 AM Break
 2:00 PM Long Break
 Topological Systems 1
 Chair: Justin Wen
 7:00 PM Robert Kirby Ultrafast Dynamics in the Topological Nodal-Line Semimetals
 ZrSiX (X = S, Se, Te)

 7:30 PM Ming Yi Room-Temperature Topological Phase Transition in Quasi-1D Bi4I4
 7:50 PM Ece Uykur Optical fingerprints of unconventional carriers in kagome metals
 8:20 PM Graham Baker Non-local microwave electrodynamics in ultrapure PdCoO2
 8:40 PM Break
 9:00 PM Poster Session 6
 Abhishek Kumar Zero-field electron spin resonance in graphene with proximity-induced spin-
 orbit coupling
 Alfred Zong Disentangling fluctuations from long-range order in a light-induced phase
 transition
 Calvin Pozderac Magnetoresistance from Guiding Center Drift of Two-Dimensional Electrons
 in a Moiré Potential
 Daniel J. Rizzo Charge-Transfer Plasmon Polaritons at Graphene/α-RuCl3 Interfaces
 David Barbalas Deviations from Matthiessen’s rule in PdCoO2 Thin Films
 Dominik M. Juraschek Highly confined phonon polaritons in monolayers of oxide perovskites
 Kota Katsumi Photoexcited nonequilibrium state of underdoped YBa2Cu3Oy studied by
 the terahertz nonlinear optical responses
 Pavel Volkov Electronic phase diagram of the excitonic insulator candidates Ta2Ni(Se1-
 xSx)5 probed by Raman scattering
 Yang Yang Raman scattering in spin-orbit coupled Mott insulators: application to
 β-Li2IrO3
 Yasunori Toda Systematic study of photoinduced quasiparticle dynamics in Bi-based
 cuprates with out-of-plane disorder

12

Wednesday, July 7
 Correlated States 2
 Chair: Natalia Perkins
10:00 AM Alain Sacuto Energy scales in cuprate superconductors revealed by electronic Raman
 spectroscopy
10:30 AM Sean Hartnoll Planckian electrons and phonons in strange metals
11:00 AM Avraham Klein A critical theory of quantum ferroelectric metals
11:30 AM Assa Auerbach Hall anomalies in strongly correlated metals and superconductors
11:50 AM Break
12:30 PM Poster Session 7
 Dániel Datz Polariton-enhanced molecular absorption in boron nitride nanotubes:
 experiments and numerical calculations
 Hector Pablo Ojeda Emergent parametric resonances and time-crystal phases in driven BCS
 Collado systems
 Ivan Mohelsky Landau level spectroscopy of Bi2Te3
 Jan Wyzula Magneto optical spectroscopy of Dirac nodal line semimetal NbAs2
 Luca Tomarchio THz and Optical Spectroscopy Study of Magnetic Topological Materials
 Mark D. Thomson Towards a complete, broadband picture of collective modes in
 incommensurate charge-density-wave systems
 Mattia Udina THz pump-probe spectroscopy: instantaneous response and coherent
 oscillations
 Niklas Wagner Resistivity Exponents in 3D-Dirac Semimetals From Electron-Electron
 Interaction
 Philipp Eck Design and realization of a triangular QSHI: Indenene
 Stephan Bron Imaging the insulator-to-metal transition of thin-film VO2 with sSNOM and
 AFM IR
 Xuanbo Feng Elucidating the role of electronic correlations in Van der Waals materials
 VSe2 and Se doped TaS2 with optical spectroscopy
2:00 PM Long Break
 Nonlinearity in Quantum Matter 1
 Chair: Mengkun Liu
7:00 PM Qiong Ma Geometry and Topology in Quantum Materials
7:30 PM Bolin Liao Time-resolved Imaging of Photocarrier Dynamics with Scanning Ultrafast
 Electron Microscope
7:50 PM Darius Torchinsky Probing Weyl Semimetal Physics with Nonlinear Photocurrents
8:20 PM Zhiyuan Sun Light induced order parameter steering in excitonic insulators
8:40 PM Break

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Thursday, July 8

 Nonlinearity in Quantum Matter 2
 Chair: Andrei Pimenov
 10:00 AM Adolfo G. Grushin linear and nonlinear optics in chiral topological metals
 10:30 AM Lara Benfatto Third-Harmonic Generation from plasma waves in cuprates
 11:00 AM Angel Rubio Floquet and cavity QED materials engineering

 11:30 AM Stefano Lupi Plasmons in Topological Materials and Highly Conductive Oxides: Linear
 and Non Linear Optical Properties

 11:50 AM Break
 12:30 PM Poster Session 8
 Aaron Sternbach Programmable hyperbolic polaritons in Van der Waals semiconductors
 Abhay Kumar Nayak Resolving topological classification through topological defects
 Adamya Prakhar Intrinsic Optical Absorption in Dirac Metals
 Goyal
 Alexey Shuvaev Solution of MIRO polarization immunity problem
 Artem Pronin Faraday rotation due to topological Hall effect in Mn2−xPtSn
 Dorri Halbertal Nano-optical studies of Moiré super-lattice domains in twisted bilayer
 graphene heterostructures
 Gergely Németh Ultrasensitive molecule detection via tip-launched graphene plasmons
 Rebecca Cervasio Probing thin films of functionalized materials by SR infrared and THz
 spectroscopy
 Tamaghna Hazra Band inversion and topology of the bulk electronic structure in FeSe_{0.45}
 Te_{0.55}
 Vaisakh Chelod Ultrafast plasmon thermalization in epitaxial graphene probed by time-
 Paingad resolved THz spectroscopy
 Yinan Dong Fizeau drag in graphene plasmonics
 2:00 PM Long Break
 Novel Optics in 2D Materials 2
 Chair: Michael Martin
 7:00 PM Alexander S. McLeod Revealing nano-plasmonics in 2D materials and correlated oxides at
 variable temperatures
 7:30 PM Liang Wu Direct imaging of the N\'eel vector switching in the monolayer
 antiferromagnet MnPSe$_3$ with strain-controlled Ising order
 7:50 PM Ji-Hee Kim Carrier multiplication for next-generation solar cells
 8:20 PM Erik Henriksen Cyclotron resonance spectroscopy in graphene and SmB6
 8:40 PM Conference Concludes

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Abstracts - Monday, June 28
Evan Constable

Vibronic processes in the quantum spin ice candidate Tb2Ti2O7

Authors: E.Constable, Y. Alexanian, K. Amelin, T. Room, U. Nagel, Z. Wang, L. Bergen, R. Ballou, J. Robert, C. Decorse, B.
Langerome, M. Verseils, J.-B. Brubach, P. Roy, E. Lhotel, V. Simonet, A. Pimenov, S. Petit and S. deBrion

Abstract: The rare-earth pyrochlores (A2B2O7: A = rare earth element, B = group IV transition metal) express a diversity of
exotic magnetism as a result of their frustrated lattice composed of corner-sharing tetrahedra. Notable examples include the
spin-ice states of Ho2Ti2O7 and Dy2Ti2O7 among many other novel and interesting phases. Within this family, one of the most
studied yet still poorly understood cases is Tb2Ti2O7 (TTO). Despite favourable long-range magnetic correlations, TTO exhibits
no conventional spin-ice nor long-range magnetic order even down to very low temperatures (~ 50 mK). One novelty of TTO is
its low-energy crystal electric-field (CEF) spectrum that defines the magnetism. A growing body of evidence suggests the peculiar
magnetic behaviour of TTO is the result of entanglement between these CEF spin degrees of freedom and the dynamics of the
frustrated lattice. The possibility that quantum fluctuations driven by spin-lattice effects could melt the magnetic order of TTO,
forming a quantum spin-liquid phase, is an intriguing and highly debated subject. As I will discuss, this possibility is supported by
a growing body of optical spectroscopic work including static THz and magneto-optical measurements. These results showcase
a hybridization between two magnetic Tb3+ CEF transitions and neighbouring phonon modes. Their interpretation suggests this
vibronic coupling provides the crucial path for normally forbidden quantum spin-flip fluctuations to occur across the CEF levels,
thus promoting spin-liquid behaviour.
 ....

Rolando Valdes Aguilar

Magnetic dynamics of honeycomb antiferromagnets

Authors: Evan V. Jasper, Timothy DeLazzer, Kate Ross, Rolando Valdes Aguilar

Abstract: I will present a comprehensive study of the terahertz dynamics of the honeycomb antiferromagnet CoTiO3. This
material has been found to host Dirac magnons at the K-points similar to the electronic bands of graphene. We studied the bulk
and surface response in this material using a new experimental technique of attenuated total reflection at terahertz frequencies.
I will show results of these measurements on CoTiO3 and in other honeycomb antiferromagnets.
 ....

Natalia Drichko

Time reversal and lattice symmetry breaking in Nd2Ir2O7 observed by Raman scattering spectroscopy

Authors: Y. Xu, J. Teyssier, T. Ohtsuki, S. Nakatsuji, D. van der Marel, N. Drichko

Abstract: Nd2Ir2O7 is a semimetal compound, where a competition between spin-orbit coupling and electronic correlations
leads to exotic physics. A Weyl semimetal state was suggested for this material in a narrow temperature range below a transition
into the insulating state at 33 K. Using polarized Raman scattering spectroscopy to study this material, we can distinguish
between magnetic excitations, and transitions over the electronic gap opened in the insulating regime. Following the evolution
of these features on cooling, we can identify two temperature regimes in the insulating state. Between 33 K and approximately
15 K we observe an electronic gap and magnon excitations related to the al-in-all-out (AIAO) order of iridium spins. Below 15 K,
where Nd spins undergo AIAO ordering, the spectrum of magnetic excitations changes, and the phonon changes reveal the lattice
deformation.

Acknowledgement: This work was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center

 15

funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0019331
 ....

Itzik Kapon

Magnetic field tuning of the valley population in the Weyl semi-metal phase of Nd$_2$Ir$_2$O$_7$

Authors: Itzik Kapon, Willem Rischau, Satoru Nakatsuji, Dirk van der Marel

Abstract: We report low-energy magneto-optical spectroscopy on the pyrochlore iridate Nd$_2$Ir$_2$O$_7$ [1]. Comparing
our data together with that of published angle-resolved photo-emission [2], we deduce a factor four mass renormalization of
the Ir d-electrons bands owing to strong correlation effects. We observe spectral changes induced by magnetic field below $T_
N^{Nd}\sim 13K$, {\em i.e.} for temperatures below which the Nd 4f electrons spin-orbital moments freeze. We accompany the
experimental data with calculations of the optical conductivity using a band structure model of the Ir 5d electrons, which takes
into account the coupling to the Nd magnetic moments and the polarization of those moments in an external magnetic field. We
conclude that at least for fields higher than 2 Tesla the correlation gap at $E_F$ is closed and the material is a Weyl semi-metal with
pairs of Weyl nodes along high symmetry directions of the cubic lattice. The magnetic field creates charge compensating pockets
of holes and electrons in different regions of momentum space, thus introducing a valley population shift that can be tuned with a
magnetic field.

[1] These experiments build on the work described in K. Wang, B. Xu, C. W. Rischau, N. Bachar, B. Michon, J. Teyssier, Y. Qiu, T.
Ohtsuki, Bing Cheng, N. P. Armitage, S. Nakatsuji and D. van der Marel; Nature Physics 16, 1194 (2020).

[2] M. Nakayama et al., PRL 117, 056403 (2016).
 ....

Nimi Bachar

Unconventional free charge in the correlated Weyl semimetal Nd2Ir2O7

Authors: K. Wang, B. Xu, C. W. Rischau, N. Bachar, B. Michon, J. Teyssier, Y. Qiu, T. Ohtsuki, B. Cheng, N. P. Armitage, S. Nakatsuji &
D. van der Marel

Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin–orbit coupling and electron–electron
interactions are believed to induce a time-reversal symmetry-broken Weyl semimetal phase characterized by pairs of topologically
protected Dirac points at the Fermi energy. However, the emergent properties in these materials are far from clear, and exotic
new states of matter have been conjectured. Here, we demonstrate optically that, at low temperatures, the free carrier spectral
weight is proportional to T^2, where T is the temperature, as expected for massless Dirac electrons. However, we do not observe
the corresponding T^3 term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the charge
carrier scattering rate approaching critical damping and the progressive opening of a correlation-induced gap at low temperatures. I
will discuss the implications of these observations in regards to the electronic band structure of pyrochlore iridates.
 ....

Berend Zwartsenberg

Spin-orbit coupling effects in Sr2IrO4

Authors: B. Zwartsenberg, R. P. Day, M.X. Na, E. Razzoli, M. Michiardi, N. Xu, M. Shi, J. D. Denlinger, G. Cao, S. Calder, K. Ueda, J.
Bertinshaw, H. Takagi, B. J. Kim, I. S. Elfimov & A. Damascelli
Sr2IrO4 hosts an insulating state that is unexpected in the context of transition metal oxides. It has been proposed that spin-orbit
coupling (SOC) is the key responsible property, as it entangles the t2g states, which enables a small Coulomb interaction to open a
gap. This proposed mechanism would extend filling and bandwidth, the canonical control parameters for insulating behavior, to the
relativistic domain. Naturally the question arises whether in this case, SOC can in fact drive the metal-insulator transition.

16

Abstract: In order to address this question, we have studied the behaviour of Sr2IrO4 when substituting Ir for Ru or Rh[1]. Both of
these elements change the electronic structure and drive the system into a metallic state. A careful analysis of filling, bandwidth,
and SOC, demonstrates that only \ac{SOC} can satisfactorily explain the transition. This establishes the importance of SOC in the
description of metal-insulator transitions and stabilizing the insulating state in Sr2IrO4.

It has furthermore been proposed that the Sr2IrO4 realizes an effective pseudo-spin 1/2 model in due to entanglement of the
t2g states into effective j=1/2 states. We test this hypothesis directly by measuring the spin-orbital entanglement using circularly
polarized spin-ARPES[2]. Our results indicate that there is a drastic change in the spin-orbital entanglement throughout the Brillouin
zone, implying that Sr2IrO4 can not simply be described as a pseudo-spin 1/2 insulator, casting doubt on previous work directly
comparing to the cuprate superconductors.

We thus find that SOC is a crucial ingredient in the ground of Sr2IrO4, however, SOC is not strong enough to fully entangle into a
jeff=1/2 state, requiring that Sr2IrO4 is described as a multi-orbital relativistic Mott insulator.

[1] Zwartsenberg et al., Nat. Phys (2020)
[2] Zwartsenberg et al., submitted (2021)
 ....

Kirill Amelin, National Institute of Chemical Physics and Biophysics, Tallinn, Estonia

Experimental observation of E8 particles in Ising-chain compounds

Authors: K. Amelin, T. Rõõm, U. Nagel, J. Viirok, J. Engelmayer, Z. Zhang, X. Wang, H. Zou, J. Yang, T. Dey, A. A. Nugroho, T. Lorenz, J.
Wu, Z. Wang

Abstract: Quantum criticality is accompanied by the emergence of exotic states of matter, which we expect to feature
unconventional dynamic properties. It is often characterized by many-body fluctuations and complex symmetry. Describing a system
near its quantum critical point is therefore an exceptionally difficult task, which makes exactly solvable models rare and especially
valuable. One example of such a model is the one-dimensional transverse-field Ising chain, which, when perturbed by a small
longitudinal field near the quantum critical point, is predicted to feature a spectrum consisting of eight particles with specific mass
ratios. The spectrum is described by the quantum integrable field theory with the symmetry of the E8 Lie algebra.
Two physical representations of the ferromagnetic and the antiferromagnetic quasi-one-dimensional Ising chains are, respectively,
CoNb2O6 and BaCo2V2O8. We measured THz absorption spectra of both compounds below their ordering temperatures using
a liquid-helium-bath cryostat for BaCo2V2O8 and a dilution refrigerator for CoNb2O6. The necessary critical transverse field
was generated using superconducting magnets, while the perturbative longitudinal field is provided by the interchain coupling
intrinsically present in these materials. As the result, we were able to observe most of the eight particles, as well as their two-
particle excitations, matching the mass ratios of the theoretical predictions. Additionally, we confirm numerical predictions that the
two-particle excitations must manifest as sharp peaks rather than overwhelming continua, which obscure the high-energy single E8
particles.
 ....

Shiming Lei, Rice University

Magnetic skyrmions in non-Gd based centrosymmetric magnet

Author: Shiming Lei

Abstract: Magnetic skyrmions are particle-like spin textures of topological origin, which exists in the real space of materials.
The intensive research activity on skyrmions has been driven not only by their fundamental interest in physics, but also by their
potential applications to next-generation memory, logic, and neuromorphic computing devices. The magnetic materials that host
skyrmions can be classified into two categories, non-centrosymmetric and centrosymmetric. So far, the majority of experimentally
identified skyrmion hosting materials are non-centrosymmetric; only three centrosymmetric materials are experimentally verified to

 17

host skyrmion lattice, and they have been limited to the Gd-based compounds, including: Gd2PdSi3, Gd3Ru4Al12, and Gd2Ru2Si2.
In this talk, I will introduce our recent efforts towards the discovery of novel non-Gd-based centrosymmetric materials that host
magnetic skyrmions.
 ....

Yuanyuan Xu, Johns Hopkins University

Importance of dynamic lattice effects for crystal field excitations in quantum spin ice candidate Pr2Zr2O7

Authors: Yuanyuan Xu, Huiyuan Man, Nan Tang, Santu Baidya, Hongbin Zhang, Satoru Nakatsuji, David Vanderbilt, Natalia Drichko

Abstract: Pr2Zr2O7 is a pyrochlore quantum spin-ice candidate. Using Raman scattering spectroscopy we probe crystal electric field
excitations of Pr3+, and demonstrate the importance of their interactions with the lattice. We identify a vibronic interaction with a
phonon that leads to a splitting of a doublet crystal field excitation at around 55 meV. We also probe a splitting of the non-Kramers
ground state doublet of Pr3+ by observing a double line of the excitations to the first excited singlet state E0g→A1g. We show that
the splitting has a strong temperature dependence, with the doublet structure most prominent between 50 K and 100 K, and the
weight of one of the components strongly decreases on cooling. We suggest a static or dynamic deviation of Pr3+ from the position
in the ideal crystal structure can be the origin of the effect, with the deviation strongly decreasing at low temperatures.
 ....

Carina Belvin, Massachusetts Institute of Technology

Revealing the soft electronic modes involved in magnetite’s Verwey transition

Authors: Carina Belvin, Edoardo Baldini, Martin Rodriguez-Vega, Ilkem Ozge Ozel, Dominik Legut, Andrzej Kozłowski, Andrzej M.
Oleś, Krzysztof Parlinski, Przemysław Piekarz, José Lorenzana, Gregory A. Fiete, Nuh Gedik

Abstract: The Verwey transition in magnetite (Fe3O4) is one of the most enigmatic phase transformations found in strongly
correlated systems. It is the first metal-insulator transition ever observed experimentally and also involves a simultaneous charge
ordering, orbital ordering, and a structural rearrangement. Due to the intricate interplay among these various degrees of freedom,
a complete description of the microscopic mechanism of this phase transition is still lacking. Recently, the low-temperature charge-
ordered structure was established as a network of three-site small polarons called trimerons. However, the dynamics of the
Verwey transition from an electronic point of view remains not understood since no collective excitations of this trimeron order
have been observed to date. In this talk, I will present our discovery of the low-energy electronic collective modes of the trimeron
network using terahertz spectroscopy. By exciting these modes coherently with an ultrashort near-infrared laser pulse, we unveil
their critical softening towards the transition temperature, demonstrating their direct involvement in the Verwey transition. These
findings represent the first observation of collective modes of any sort displaying a critical softening in magnetite and thus shed
new light on the long-sought cooperative mechanism responsible for this transition to the exotic ground state of magnetite.
 ....

Valentina Brosco, Institute for Complex Systems, Consiglio Nazionale delle Ricerche, Rome, Italy

Rashba-metal to Mott-insulator transition - spectral signatures

Authors: Valentina Brosco and Massimo Capone

Abstract: The recent discovery of materials featuring strong Rashba spin-orbit coupling (RSOC) and strong electronic correlation
raises questions about the interplay of Mott and Rashba physics. In this talk, we show that RSOC strongly favors metallic phases and
it competes with Mott localization, affecting the physics of the metallic and Mott insulating phases and, consequently, of the Mott
transition connecting the Rashba metal and Mott insulator.
The crucial features of the metallic state and the mechanism behind the metallization are analyzed by different approaches
providing a clear physical picture and identifying the spectral signatures of the Rashba-Mott interplay. Our results suggest the
possibility of exploiting the tunability of Rashba spin-orbit coupling to control transport in strongly correlated materials and they

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may be extremely relevant to account for the transport properties of correlated materials oxides heterostructures, surface alloys,
and polar semiconductors.
 ....

Wibke Bronsch, Elettra Sincrotrone Trieste

Time- and Angle-Resolved Photoemission Study on Bulk VSe2

Authors: Wibke Bronsch, Manuel Tuniz, Denny Puntel, Alessandro Gianmarino, Fulvio Parmigiani and Federico Cilento

Abstract: By means of time- and angle-resolved photoemission spectroscopy (tr-ARPES), we investigate the effect of the phase
transition into the charge density wave (CDW) phase on the equilibrium and out-of-equilibrium electronic band structure of the
transition metal dichalcogenide VSe2. The electronic band structure of VSe2 has recently been subject of investigation ranging from
the bulk to the monolayer regime, in search for the manifestation of the opening of the band gap in its CDW phase [1,2]. At present,
few time-resolved studies on the effect of optical excitation are available on the ultrafast timescales [1,3]. In our contribution we
present a study on the bulk material. By changing the polarization of the probe pulses tr-ARPES allow us to disentangle the d-like
and p-like states from the V and Se valence bands respectively, and selectively probe their dynamics. We observe faster initial
relaxation dynamics when probing the d-states with p-polarized light. When moving across the critical temperature for the CDW
phase transition, our tr-ARPES data show indication for a change in the relative population of the bands close to the Fermi level
which lasts for a few picoseconds after the photoexcitation.

[1] Biswas et al., Nano Letters 21, 1968-1975 (2021).
[2] Umemoto et al., Nano Research 12, 165-169 (2019).
[3] Majchrzak et al., arXiv:2011.06358v1 (2020).
 ....

Martin Dressel, Universität Stuttgart, 1. Physikalisches Institut

Dielectric Catastrophe at the Mott Transition

Authors: M. Dressel, R. Rösslhuber, Y. Saito, A. Pustogow, E. Uykur, Y. Tan and V. Dobosavljevic

Abstract: A Mott insulator becomes metallic when the effect of correlations decreases. In the case of full frustration, a first-order
phase transition is expected up to some critical endpoint. Above Tcrit there might be some crossover and quantum critical behavior.
But what happens below?
We start with the quantum spin liquid k-(BEDT-TTF)2Cu2(CN)3 and tune the electronic bandwidth either by external pressure or
by chemical substitution. DC resistivity confirms the insulator-metal transition (and even superconductivity in between). Optical
spectroscopy reveals the development of the Drude-like contribution given evidence for coherent transport. Most surprising,
however, is the divergency of the dielectric permittivity at the Mott insulator-to-metal transition at temperatures T < Tcrit = 20
K with eps1 = 10^5 and more. We show that the dielectric catastrophe is a fingerprint of the first-order phase transition where
metallic and insulating regions coexist spatially. The percolative nature of the Mott transition dominates the low-frequency
behavior compared to the closing of the Mott-Hubbard gap seen in the infrared range. All experimental trends are captured by
dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory.

Ref.: A. Pustogow et al., npj Quantum Materials 6, 9 (2021); R. Rösslhuber et al., Phys. Rev. B 103, 125111 (2021); Y. Saito et al.,
arXiv:1911.06766
 ....

 19

Giorgio Sangiovanni, University of Wuerzburg / Institute for theoretical physics and astrophysics

Design and realization of topological Dirac fermions on a triangular lattice

Authors: Maximilian Bauernfeind, Jonas Erhardt, Philipp Eck, Pardeep K. Thakur, Judith Gabel, Tien-Lin Lee, Joerg Schaefer, Simon
Moser, Domenico Di Sante, Ralph Claessen and Giorgio Sangiovanni

Abstract: The key to engineer large-gap quantum spin Hall insulators is a strong spin-orbit interaction. In Kane and Mele’s
suggestion for honeycomb layers, SOC is promoted via a relatively weak second neighbor hopping process. Bismuthene however
has impressively proven the superiority of local/atomic SOC of the in-plane p-orbitals. A new possibility arises by halving the
bismuthene honeycomb lattice but enriching the orbital subspace, i. e. considering a full p-basis on a triangular lattice. Here, we
conceive and realize for the first time a triangular QSHI, ‘’indenene’’, a triangular monolayer of indium on SiC(0001) exhibiting
non-trivial valley physics as a consequence of strong local spin-orbit coupling. By means of tunneling microscopy of the 2D bulk
we identify the quantum spin Hall phase of this triangular lattice, unveiling how a hidden honeycomb connectivity emerges from
interference effects of Bloch $p_x\pm i p_y$-derived wave functions.
Severino Adler, University of Würzburg / TU Wien
From Mott to Dirac Fermions via Van der Waals Stacking
José M. Pizarro, Severino Adler, Karim Zantout, Thomas Mertz, Paolo Barone, Roser Valentí, Giorgio Sangiovanni, and Tim O.
Wehling
Modelling Dirac systems via stacking of monolayers has captured great attention over the last decade. The standard approach is
to stack almost uncorrelated materials to obtain topological non-trivial, sometimes moderatly correlated states. Here we take the
opposite approach, stacking two mono-layers of 1T-TaSe2, which features a Mott-insoluting star-of-david (SOD) charge density
wave, to obtain a topologically non-trivial and moderately correlated system. If stacked in a fashion such that the center of the
SODs form a honeycomb lattice the bilayer can be well described via a Kane-Mele model, featuring sizeable spin-orbit coupling
and local interaction strength. The system turns out to be close to a quantum phase transition between a quantum spin Hall and
an antiferromagnetic insulator and can be tuned into the a topologically trivial state with a perpendicular electric field. Further, we
analyse the effect of an 180 degrees twisting angle on the topology, via considering a generalised version of the Kane-Mele model.
 ....

Jie Shan

Electrons in 2D semiconductor moiré superlattices

Author: Jie Shan

Abstract: When two van der Waals materials of slightly different orientations or lattice constants are overlaid, a moiré pattern
emerges. The moiré pattern introduces a new length scale, many times the lattice constant of the original materials, for Bragg
scattering of Bloch electrons in each layer. This gives rise to moiré minibands and rich emergent phenomena. In this talk I will
discuss recent experiments on angle-aligned semiconductor heterobilayers, which exhibit remarkable correlated insulating states.
 ....

Yiping Wang

Modulation Doping via a 2D Crystalline Acceptor

Author: Yiping Wang

Abstract: Two-dimensional (2d) nano-electronics, plasmonics, and emergent phases require clean and local charge control, calling
for layered, crystalline acceptors or donors. Here, we demonstrate that the large work function narrow-band Mott insulator RuCl3
enables modulation doping of exfoliated single and bilayer graphene. Our Raman measurements show high hole densities up to
1014cm-2 in RuCl3/mlg/RuCl3 heterostructures, 3*1013cm-2 in mlg RuCl3 heterostructures and 6*1013cm-2 in bilayer graphene
(blg) RuCl3 heterostructures. In addition, our study suggest photovoltage devices, charge transfer control via twist angle, and

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charge transfer through hexagonal boron nitride (hBN).
 ....

Masahiro Sato

Nonlinear Optical Responses in Quantum Spin Liquids

Authors: Minoru Kanega, Tatsuhiko N. Ikeda and Masahiro Sato

Abstract: Laser science has continuously stimulated the research for laser-driven phenomena and nonequilibrium physics in solid
matters. Among phases in matters, quantum spin liquids (QSLs) are one of the most attractive many-body states and researchers
have explored various experimental ways of hunting their nature. Most of thermodynamic (static) quantities of QSLs are featureless
and dynamical observables can be often useful to detect their nature. The research of QSLs with laser is thereby an attractive
research direction. In fact, the recent development of THz-laser science enables us to directly control magnetic excitations since THz
photon energy is comparable to that of magnetic excitations. Under this background, recently we have theoretically tried to build
a bridge between QSLs and THz laser. In this conference, I will focus on our theory for THz-laser driven high-harmonic generation
(HHG) in QSLs. HHG is a simple nonlinear optical effect, and both its theory and experiment have been rapidly developed in the
recent years. So far researchers have concentrated on the HHG in conducting electron systems because the light-charge coupling is
strongest among light-matter interactions. However, HHG through the light-spin coupling is expected to be realized if applied THz
laser is strong enough. It has been indeed observed in some experiments. We have developed the microscopic theory for THz-laser
driven HHG in 1D QSLs and 2D Kiteav spin liquids. We show that some features of QSLs are revealed from the HHG spectra. In the
conference, I will report our result of HHG by focusing on its essential points.
 ....

Shuqiu Wang

Scattering Interference Signature of a Pair Density Wave State in the Cuprate Pseudogap Phase

Authors: Shuqiu Wang, Peayush Choubey, Yi Xue Chong, Weijiong Chen, Wangping Ren, H. Eisaki, S. Uchida, P.J. Hirschfeld and J.C.
Séamus Davis

Abstract: An unidentified quantum fluid designated the pseudogap (PG) phase is produced by electron-density depletion in the
CuO2 antiferromagnetic insulator. Current theories suggest that the PG phase may be a pair density wave (PDW) state characterized
by a spatially modulating density of electron pairs. Such a state should exhibit a periodically modulating energy gap Δ_P (r) in real-
space, and a characteristic quasiparticle scattering interference (QPI) signature Λ_P (q) in wavevector space. By studying strongly
underdoped Bi2Sr2CaDyCu2O8 at hole-density ~0.08 in the superconductive phase, we detect the 8a0-periodic Δ_1 (r) modulations
signifying a PDW coexisting with superconductivity. Then, by visualizing the temperature dependence of electronic structure from
the superconducting into the pseudogap phase, we find evolution of the scattering interference signature Λ_P (q) as predicted
specifically for an 8a0-periodic PDW. These observations from the real- and wavevector-space are all consistent with a transition
from a PDW state coexisting with d-wave superconductivity to a pure PDW state in the Bi2Sr2CaDyCu2O8 pseudogap phase.

Funding: Y.X.C. and J.C.S.D. acknowledge support from the Moore Foundation’s EPiQS Initiative through Grant GBMF9457. J.C.S.D.
acknowledges from Science Foundation Ireland under Award SFI 17/RP/5445. W.C. and J.C.S.D. acknowledges support from the
Royal Society through Award R64897. S.W., W.R. and J.C.S.D. acknowledge support from the European Research Council (ERC) under
Award DLV-788932.
 ....

 21

Tuesday, June 29
Ingrid Barcelos

Probing Polaritons in 2D Materials with Synchrotron Infrared Nanospectroscopy

Authors: Ingrid D. Barcelos, Hans A. Bechtel, Christiano J. S. de Matos, Dario A. Bahamon, Bernd Kaestner, Francisco C. B. Maia and
Raul O. Freitas

Abstract: Polaritons, which are quasiparticles composed of a photon coupled to an electric or magnetic dipole, are a major focus
in nanophotonic research of van der Waals (vdW) crystals and their derived 2D materials. For the variety of existing vdW materials,
polaritons can be active in a broad range of the electromagnetic spectrum (meVs to eVs) and exhibit momenta much higher than the
corresponding free-space radiation. Hence, the use of high
momentum broadband sources or probes is imperative to excite those quasiparticles and measure the frequency-momentum
dispersion relations, which provide insights into polariton dynamics. Synchrotron infrared nanospectroscopy (SINS) is a technique
that combines the nanoscale spatial resolution of scattering-type scanning near-field optical microscopy with ultrabroadband
synchrotron infrared radiation, making it highly suitable
to probe and characterize a variety of vdW polaritons. Here, we present the advances enabled by SINS on the study of key photonic
attributes of far- and mid-infrared plasmon- and phonon-polaritons in vdW and 2D crystals.
 ....

Hanan Herzig Sheinfux

Bound in the continuum modes in indirectly-patterned hyperbolic media

Authors: Hanan Herzig Sheinfux, Lorenzo Orsini, Minwoo Jung, Iacopo Torre, Matteo Ceccanti, Rinu Maniyara, David Barcons Ruiz,
Sebastian Castilla, Niels C.H. Hesp, Eli Janzen, Valerio Pruneri, James H. Edgar, Gennady Shvets, Frank H.L. Koppens

Abstract: The general premise of nanophotonics involves shrinking light to the subwavelength nanometric scale. By compressing
light into the volume of a nanocavity, the interaction of light with matter is dramatically enhanced. Recent innovations in nanocavity
design have pushed the volume of such cavities deep into the nanoscale, but shrinking light typically comes at a cost – absorption
losses, which plague all existing nanocavity designs and the typical quality factor of all such cavities is on the order of 10. A possible
route to strong nanoscale confinement lies with hyperbolic Phonon polaritons and in particular using indirectly defined cavities.
However, doing so requires a different approach to confinement, inspired by bound in continuum mode physics, and bound modes
in the continuum modes have never been observed in nanophotonics. Here, we bring the BIC concept to the nanoscale and use it
to achieve record breaking levels of optical confinement. We introduce and demonstrate a novel multimodal reflection mechanism
of the ray-like optical excitations in hyperbolic materials. Using near-field microscopy, we observe mid-IR confinement in BIC-
based nanocavities with volumes down to 23x23x3 and quality factors above 100 – a dramatic improvement in several metrics
of confinement. This alliance of HyM with BICs yields a radically novel way to confine light and is expected to have far reaching
consequences wherever strong optical confinement is utilized, from ultra-strong light-matter interactions, to mid-IR nonlinear optics
and a range of sensing applications.
 ....

Jeremy Levy

Gate-Tunable Optical Nonlinearities and Extinction in Graphene/LaAlO3/SrTiO3 Nanostructures

Authors: Erin Sheridan, Lu Chen, Jianan Li, Qing Guo, Shan Hao, Muqing Yu, Ki-Tae Eom, Hyungwoo Lee, Jung-Woo Lee, Chang-Beom
Eom, Patrick Irvin, Jeremy Levy

Abstract: We explore the ultrafast optical response of graphene subjected to intense (~106 V/cm) local (~10 nm) electric fields.
Nanoscale gating of graphene is achieved using a voltage-biased, SrTiO3-based conductive nanowire junction “written” directly

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under the graphene and isolated from it by an insulating ultrathin (99.9%) are observed in the VIS-NIR and SFG spectral ranges,
in parameter regimes that are positively correlated with the enhanced nonlinear response. The observed graphene-light interaction
and nonlinear response are of fundamental interest and open the way for future exploitation in graphene-based optical devices such
as phase shifters, modulators, and nanoscale THz sources.

Reference: https://pubs.acs.org/doi/10.1021/acs.nanolett.0c01379
 ....

Alexey Kuzmenko

Infrared nanoscopy of polaritons in functional oxides and interfaces

Authors: Y. Zhou, A. Bercher, A. Waelchli, W. Luo, A. M. Boselli, J.-M. Poumirol, I. Ardizzone, J. Teyssier, D. van der Marel, S. Gariglio,
J.-M. Triscone and A.B. Kuzmenko

Abstract: FunctionalqQuantum oxides exhibit a remarkable variety of ordering phenomena that can be useful for applications,
such as (multi-)ferroicity, superconductivity and metal-insulator transitions. Typically, near the ordering temperature, different
phases coexist at the nanoscale. Furthermore, some of the important effects appear at the nanometer-thick interfaces between
the different oxide layers, exemplified by the famous LAO/STO system ([1-3]). Infrared spectroscopy probes charge, spin and lattice
dynamics and therefore is extremely useful to elucidate the physical origin of various ordered phases. However, conventional infrared
measurements are diffraction limited and do not provide nanoscale resolution. On the other hand, the technique of scattering-type
scanning near-field optical microscopy (s-SNOM) [4], based on the near-field interaction between an atomic-force microscope (AFM)
tip and the sample, overcomes the diffraction limit, while keeping all the advantages of conventional spectroscopy. Recently, it has
been extended to broad-temperature range operation down to 5 K, opening the opportunity to optically examine the mentioned
phenomena with nanoscale resolution.

In this contribution, we will present SNOM mapping of LAO/STO systems and nanostructures [5,6], as a function of temperature,
the laser wavelength and the gate voltage. We find that the s-SNOM signal and polariton propgation are highly sensitive to the
density and the mobility of the charge carriers in the 2DEG, which is explained by the formation of coupled plasmon-phonon
polariton modes at the interface. We also demonstrate that SNOM can be used to map spatially inhomogeneous structures, such as
AFM-written conducting wires, lithographically made nanostructures and domain walls in the materials potentially useful in oxide
electronics.

References:
[1] A. Ohtomo and H.Y. Hwang, Nature 427, 423 (2004).
[2] S. Thiel, G. Hammerl, A. Schmehl, C.W. Schneider and J. Mannhart, Science 313, 1942 (2006).
[3] A.D. Caviglia, S. Gariglio, N. Reyren, D. Jaccard, T. Schneider, M. Gabay, S. Thiel, G. Hammerl, J. Mannhart and J.M. Triscone, Nature
456, 624 (2008).
[4] F. Keilmann and R. Hillenbrand, Phi. Trans. R. Soc. Lond. A 362, 787 (2004).
[5] W. Luo, M. Boselli, J.-M. Poumirol, I. Ardizzone, J. Teyssier, D. van der Marel, S. Gariglio, J.-M. Triscone and A.B. Kuzmenko, Nature
Communications 10, 2774 (2019).
[6] M. Boselli, G. Scheerer, M. Filippone, W. Luo, A. Waelchli, A. B. Kuzmenko, S. Gariglio, T. Giamarchi and J.-M. Triscone, Phys. Rev. B,
in press (2021), arXiv:2009.07867.
 ....

 23

Amalia Coldea

Anomalous magnetotransport of the nematic FeSe and related chalcogenides

Author: Amalia Coldea

Abstract: A nematic electronic state that breaks the rotational symmetry of the lattice can potentially
promote unique conditions for anomalous scattering relevant for superconductivity. Here, I present magnetotransport behaviour
of the superconducting FeSe S across a nematic phase transition probed in magnetic fields up to 38T. Inside the nematic phase, the
transverse magnetoresistance is very large and anomalous and the Hall coefficient changes sign both as a function of temperature
and substitution, beyond the expectation for a two-band model system. A region of linear resistivity is detected inside the nematic
phase, where spin fluctuations are present. Near the nematic end point, the resistivity displays a T dependence [1,2,3] and the
divergent critical fluctuations are suppressed by a finite nematoelastic coupling [2]. We discuss the role played by the high mobility
bands and the scattering processes with spin fluctuations, phonos and impurities on the overall magnetotransport behaviour of FeSe
S [3]. I will also compare the behaviour of bulk single crystals as compared to FeSe thin flakes [4].

[1] M. Bristow et al., PRR 2,013309 (2020);
[2] P. Reiss et al., Nat. Phys. 16,89 (2020);
[3] A.I. Coldea, arXiv:2009.05523 (2020); https://doi.org/10.3389/fphy.2020.594500
[4] L. Farrar et al., in preparation (2021);
 ....

Roberta Citro

Topological superconductivity by orbital confinement in oxide nanowires

Authors: J. Settino , C. A. Perroni, V. Cataudella, M. Cuoco and R. Citro

Abstract: We determine the conditions to achieve topological superconductivity in an oxide nanowire in the presence of an in-
plane external magnetic field. We show that lateral confinement introduces a splitting of the d orbitals that alters the orbital energy
hierarchy and significantly affects the topological phase diagram. The increase of the nanowire thickness leads to dense distribution
of topologically nontrivial domains when orbital population inversion takes place. We also demonstrate that the electronic structure
exhibits an orbital-dependent magnetic anisotropy which affects the character of theMajorana bound states (MBSs) and gives rise to
a rich behavior of spin-orbital polarization.
These findings highlight the strong interplay of spin-orbital degrees of freedom due to the competition of the orbital Rashba
interaction, atomic spin-orbit coupling, and structural distortions in oxides.
 ....

Marco Marciani

Resistivity anisotropy in nematic FeSe from multiorbital Boltzmann equation

Authors: Marco Marciani and Lara Benfatto

Abstract: Iron pnictides have drawn the attention of the high-Tc superconductor community due to the peculiar interplay between
magnetism, superconductivity and electronic nematicity. To better single out such physics many studies have focused on the normal
phase of these materials. A still debated issue is the nature of the structural transition in FeSe. Indeed, the marked anisotropy
of the transport properties and the reconstruction of the Fermi surface at Ts=90 K clearly point towards an electronic nature of
the order. Nonetheless, the exact form of the electronic order parameter is still quite controversial. Here I will show how bulk
transport properties can be used to discriminate among different models for the nematic order[1]. To this end, I will present first
the analytical solution of a generic multiorbital Boltzmann equation including scattering from impurities. Secondly I will discuss its
implications within different scenarios for the nematic phase. Interestingly, a recent proposal[2] invoking d_xy orbital order along
with the well-established xz/yz orbital splitting turns out to provide an excellent description of the measured resistivity anisotropy in
experiments[3].

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