Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V64: Greene Dissertation Award SessionInvited Live Prize/Award
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Sponsoring Units: DCMP DMP GSNP Chair: Richard Greene, University of Maryland, College Park |
Thursday, March 18, 2021 3:00PM - 3:36PM Live |
V64.00001: Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics (2020): Beyond-Classical Quantum Computation at Google-AI Quantum Invited Speaker: Xiao Mi Over the past decade, rapid progress in quantum engineering has allowed full fabrication and control of superconducting quantum processors with over 50 qubits and full planar connectivity, as exemplified by Google’s Sycamore processor. Using random circuits carefully designed to randomly explore the immense Hilbert space with 1016 dimensions, a bit-string sampling task that proves difficult for classical computation has been recently demonstrated on Sycamore. In this presentation, I will first detail the formulation and execution of the original “quantum supremacy” experiment [1]. I will then describe current works being done in our group, with a particular emphasis on the efforts to discover useful quantum computing applications in the Noisy Intermediate-Scale Quantum (NISQ) era. As an example, I will present preliminary experimental results on using Sycamore to study the physics of scrambling and thermalization in quantum circuits that are challenging to analyze or simulate classically [2]. |
Thursday, March 18, 2021 3:36PM - 4:12PM Live |
V64.00002: Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics (2020): Probing Chiral Excitations with Raman Scattering Invited Speaker: Hsiang-Hsi Kung The properties of quantum materials are dominated by electronic correlations, which often leads to novel emergent phenomena and spontaneous symmetry breaking at low temperatures or material interfaces. These underlying correlations are encoded in the collective excitations, which are sometimes hidden from experimental probes. Here, we use polarization-resolved Raman scattering to directly probe the collective modes with the symmetry of a pseudovector. In the heavy-fermion metal, URu2Si2, the A2g collective mode uniquely couples to the reflection symmetry breaking ground state in the low-temperature phase -- a chirality density wave that was hidden from other spectroscopic tools in the past [1,2]. Whereas on the surface of the 3D topological insulator, due to the strong Rashba spin-orbit coupling, the electrons acquire chiral spin textures that result in novel collective modes and composite particles. In the example of Bi2Se3, we observed an A2 mode as the collective spin excitation from the surface states [3], and circularly polarized photoluminescence from chiral excitons [4]. |
Thursday, March 18, 2021 4:12PM - 4:48PM Live |
V64.00003: Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics: Discovery of magnetic Weyl semimetals and topological chiral crystals Invited Speaker: Ilya Belopolski The discovery of novel, robust topological materials is essential for advancing the state-of-the-art in topological physics. In this talk, I will discuss two fundamental strategies, using intrinsic magnetic order and structural crystalline chirality, which we have recently developed to uncover exotic quantum materials dominated by robust topological electronic states. I will first present the experimental observation of Weyl fermion loops and topological drumhead surface states by ARPES in the room-temperature ferromagnet Co2MnGa [1]. Then, I will provide evidence that Co2MnGa at the Fermi level is dominated by Berry curvature concentrated by the Weyl loops, driving a giant anomalous Hall effect and record-high anomalous Nernst effect, up to room temperature. Next, I will present our discovery by ARPES of the near-ideal topological chiral crystals RhSi and CoSi [2]. After reviewing our rigorous criteria for the experimental detection of topological Fermi arcs by ARPES [3,4], I will present our observation in these materials of giant helicoid Fermi arc surface states, arising from bulk topological chiral fermions with maximal momentum-space separation. Time permitting, I will comment on a third fundamental strategy, topological multilayers, which offers new opportunities for the future discovery of highly-tunable topological magnets [5]. |
Thursday, March 18, 2021 4:48PM - 5:24PM Live |
V64.00004: Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics: Imaging electronic wavefunctions and interactions on the surface of bismuth Invited Speaker: Mallika Randeria Quantum materials provide a rich platform for realizing novel phenomena that can emerge from a confluence of electronic interactions, symmetry breaking and topology. In this talk, I will discuss scanning tunneling microscope experiments that explore the role of electron-electron interactions and their tunability on the surface of bismuth. In the presence of an applied magnetic field, the bismuth surface states enter the quantum Hall regime, in which our spectroscopic measurements reveal a number of exotic ordered ground states. Specifically, we observe a nematic phase with broken rotational symmetry and a ferroelectric phase that carries a dipole moment. We use the scanning tunneling microscope to directly visualize the wavefunctions of these broken symmetry phases. Furthermore, we image local nematic domains and find counter-propagating one-dimensional quantum Hall edge modes at their boundaries. We can change the number of edge modes at the domain walls to realize strikingly different regimes where the boundary is either metallic or insulating, in accordance with theory for a new class of interacting Luttinger liquids. |
Thursday, March 18, 2021 5:24PM - 6:00PM Live |
V64.00005: Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics (2020): Delafossite Oxides: natural, ultra-pure metal-insulator heterostructures Invited Speaker: Veronika Sunko Delafossite oxides are layered compounds, which can be thought of as natural heterostructures of triangularly coordinated metallic sheets and transition metal oxide blocks. A fascinating range of electronic states can be found both in their bulk and on their surfaces, including extremely high conductivity1 in PtCoO2 and PdCoO2, maximal Rashba-like spin-splitting2 on the transition metal terminated surfaces of PtCoO2, PdCoO2 and PdRhO2, Stoner ferromagnetism3 on the Pd-terminated surface of PdCoO2 and, perhaps most remarkably, an intertwined spin-charge response due to a Kondo coupling between metallic and Mott insulating layers4 in PdCrO2. In my PhD I have investigated all of these states experimentally with angle resolved photoemission, and have collaborated with theorists in reaching theoretical understanding of the observed behaviour. |
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