290S/290K Quantum Materials Seminar speaker Aris Alexandradinata (UC Santa Cruz), Wednesday, May 10 (yes this is May 2023) at 2 pm in Physics South 402

Time/Venue Wednesday, May 10 at 2 pm Physics South 402
Host Joel Moore
Title Nonlinear optical phenomena of topological materials
Abstract
tba

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290S/290K Quantum Materials Seminar speaker Junyeong Ahn (Harvard), Wednesday, January 18, 2023 at 2 pm in Physics South 402

Time/Venue Wednesday, January 18 at 2:00 pm Pacific Time in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title tba
Abstract tba

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290S/290K Quantum Materials Seminar speaker Aaron Szasz (LBL) Spring date tba at 2 pm in Physics South 402

Time/Venue Date tba at 2 pm in Pacific time in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title tba
Abstract: tba

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290S/290K Quantum Materials Seminar speakers Ryan Day and another speaker tbd (both UC Berkeley) on Wednesday, December 14 at 2:00 pm in Physics South 402

Time/Venue Wednesday, December 14 at 2:00 pm PST in Physics South 402
Host Bob Birgeneau
Speaker Ryan Day (Analytis Group)
Title tbd
Abstract tbd
Speaker tbd
Title
 tbd
Abstract
 tbd

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290S/290K Quantum Materials Seminar speaker Wednesday December 7 Thomas Scaffidi (UC Irvine)

Time/Venue Wednesday, December 7 at 2:00 pm Pacific Time in Physics South 402
 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
Title tba
Abstract tba

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290S/290K Quantum Materials Seminar speaker Ashley Cook (Max Planck Institute for the Physics of Complex Systems) Wednesday, November 16 at 2 pm in Physics South 402

Time/Venue Wednesday, November 16 at 2 pm in Pacific time in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Topological skyrmion phases of matter
Title: Topological skyrmion phases of matter
Abstract: Symmetry-protected topological phases of matter have long been classified based on mappings from the full Brillouin zone to the space of projectors onto occupied states. This is the basis of the ten fold way classification scheme. Here, we show effectively non-interacting topological phases are associated with mappings from the Brillouin zone to the space of other observables. We specifically consider topological phases of the spin degree of freedom of the ground state, protected by a generalized particle-hole symmetry, which are independent of the topological phases of the full set of degrees of freedom of the ground state. We show these phases realize distinctive momentum-space skyrmionic spin textures, and exhibit exotic bulk-boundary correspondence, which we characterize in detail by introducing the symmetry-enriched partial trace and symmetry-enriched slab entanglement spectrum. Non-trivial spin skyrmion number corresponds to additional spin-momentum-locking at the edge in slab geometries, and topologically-protected gapless boundary modes even when the projector topological invariant is trivial. We present recipes for constructing myriad toy models of these phases, and also explore consequences of this physics in transition metal oxide superconductors as the generalized particle-hole symmetry occurs in centrosymmetric superconductors. When spin is not conserved due to non-negligible atomic spin-orbit coupling, we find two kinds of topological phase transitions are possible. The second kind occurs without the closing of the minimum direct bulk energy gap while respecting the symmetry protecting the topological phase, due to the minimum spin magnitude going to zero somewhere in the Brillouin zone. This type-II topological phase transition serves as the first-known contradiction of the flat-band limit assumption, widely-used since the early 1980’s.

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Special 290S/290K Quantum Materials Seminar speaker Nikita Astrakhantsev (Uni Zürich) Monday, November 14 at 11 am in Physics South 325

Time/Venue Monday, November 14 at 11 am in Physics South 325
 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Spin-liquid states on the pyrochlore lattice and Rydberg atoms
simulator
Abstract The XXZ model on the three-dimensional frustrated pyrochlore
lattice describes a family of rare-earth materials showing signatures of
fractionalization and no sign of ordering in the neutron-scattering
experiments. The phase diagram of such XXZ model is believed to host
several spin-liquid states with fascinating properties, such as emergent
U(1) electrodynamics with emergent photon and possible
confinement-deconfinement transition. Unfortunately, numerical studies
of such lattice are hindered by three-dimensional geometry and absence
of obvious small parameters.
In this talk, I will present my work [Phys. Rev. X 11, 041021] on the
variational study of the pyrochlore XXZ model using the RVB-inspired and
Neural-Network-inspired ansätze. They yield energies better than known
results of DMRG at finite bond dimension. With these wave functions, we
study the properties of frustrated phase at the Heisenberg point, and
observe signatures of long-range dimer correlations.
Lastly, I will sketch the prospects of using the Programmable Rydberg
Simulator platform for the study of these spin-liquid states. I will
construct two possible embeddings of the pyrochlore XXZ model onto the
Rydberg atoms simulator, employing the notion of spin ice and
perturbative hexagon flip processes.

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290S/290K Quantum Materials Seminar speakers Yi Lin and Luke Pritchard Cairns (both UCB) on Wednesday, November 9 at 2:00 pm in Physics South 402

Time/Venue Wednesday, November 9 at 2:00 pm PST in Physics South 402
Host Bob Birgeneau
Speaker Yi Lin (Lanzara Group)
Title
Mapping Ultrafast Excitonic Phenomena in 2D Materials by Using Time-Resolved ARPES
Abstract
Excitonic correlations between electrons and holes play the key role for understanding the optical phenomena, many-body interactions and exotic phase transitions in semiconducting materials and excitonic insulators, which have been conventionally studied by optical spectroscopies. In this talk, we present our experimental and theoretical work toward probing ultrafast excitonic phenomena in 2D materials by using extreme-UV time- and angle-resolved photoemission spectroscopy (XUV-trARPES). By photoemitting the electrons from different types of correlated electron-hole gases in the material, we made ultrafast movies of electronic band structure impacted by the excitonic correlations. Our results visualized a non-resonant exciton formation process and revealed exciton-driven band renormalization effects, featuring surprising bandgap opening and band flattening. Our work demonstrates a new pathway for studying excitonic many-body phenomena by using photoemission techniques under a single-particle narrative fully in energy, momentum and time.
Speaker 
Luke Pritchard Cairns (Analytis Group)
Title
Tracking the evolution from isolated dimers to many-body entanglement in NaLuxYb1−xSe2
Abstract NaYbSe2 belongs to a recently discovered class of Yb delafossites, the majority of which have been shown to exhibit the hallmarks of a quantum spin liquid (QSL) – for example an absence of long-range magnetic order and a large anomalous heat capacity at the lowest measurable temperatures. However, given the small regions of parameter space QSL states can occupy for the triangular lattice, it seems unlikely that such a varied collection of compounds should all satisfy the constraints. In this study we look to diverge from the typical investigation of a QSL, and have instead doped NaYbSe2 with non-magnetic Lu. In this way, we are able to investigate the evolution of magnetic correlations, from isolated dimers, through the percolation transition and building towards the highly-correlated many-body entangled state in NaYbSe2. We hope that this might shed light on the proposed QSL state in this compound, and also the broader class of materials.

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290S/290K Quantum Materials Seminar speaker Thais Victa Trevisan (new to UCB!) Wednesday, November 2 at 2 pm in Physics South 402

Time/Venue Wednesday, November 2 at 2 pm in Pacific time in 402 Physics South and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Joel Moore
Title Tuning magnetic symmetries and topology with bicircular light
Abstract Light-matter interaction is a powerful tool to manipulate the electronic properties of materials. Coherent light can be carefully tailored to break selected symmetries and stabilize phases of matter otherwise absent. This technique is called Floquet engineering and has received increasing attention in condensed matter physics in the past few years. In this talk, we theoretically analyze the effects of shining a bicircular light (BCL) on Dirac semimetals and topological insulators. BCL consists of a superposition of two circularly polarized light beams with frequencies that are integer multiples of each other. The resulting electric field traces a rose curve whose shape and orientation can be controlled by light parameters. A distinctive feature of BCL is its capability to simultaneously break time-reversal and spatial inversion symmetry, which leads to the realization of sought-after magnetic topological states. Another outcome of BCL driving is a dynamical tunability of the position and energy of topologically protected nodes of the band structure, resulting in a controlled modulation of the gyrotropic magnetic effect.

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Special 290S/290K Quantum Materials Seminar speaker Ethan Lake (MIT) Thursday, October 27 at 4 pm in Physics South 402

Time/Venue Thursday, October 27 at 4 pm in Pacific time in Physics South 402 and via Zoom:
https://berkeley.zoom.us/j/99523499113pwd=REovb3pyam03WXQwbEhrU3dqNHZvdz09

Meeting ID: 995 2349 9113 Passcode: 600704
Host Ehud Altman
Title Renormalization group quantum circuits for 1d SPT phases
Abstract Suppose one is handed the ground state wavefunction of a local Hamiltonian. How does one determine the phase of matter that this ground state belongs to? In this talk, I will describe a way of answering this question for 1d symmetry protected topological phases using `RG quantum circuits’: unitary circuits that test whether or not their inputs belong to a particular phase. These circuits are constructed from only a small amount of universal data, and simulate renormalization group flow with the help of a simple error correction protocol. This talk is based on soon-to-appear work with Shankar Balasubramanian and Soonwon Choi.

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