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Condensed Matter Seminar

Qi Zhou, Purdue University
Speaker: Qi Zhou, Purdue University Title: Synthetic quantum matters in ultracold atoms: from topological defects to curved spaces. Abstract: The well controllable atomic samples have allowed physicists to access a wide range of quantum phenomena unattainable in other systems. I will discuss a few such examples. The first example includes topological defects in high dimensions, ranging from Yang monopoles to continuous topological defects in five dimensions. A Yang monopole as a fundamental ingredient in non-abelian gauge theories was proposed back to seventy years ago. It was recently delivered for the first time in an experiment by tailoring laser-atom couplings in a five-dimensional parameter space. Moreover, highly tunable interactions between atoms could turn a Yang monopole into a much broader range of continuous topological defects. In another example, I will show how to create synthetic curved spaces, including a Hall cylinder and a Hall torus. Coupling internal degrees of freedom and orbital motions of ultracold atoms allows us to bypass constraints from physical laws and thread a finite effective magnetic flux through the surface of a torus or a cylinder. This development opens the door to exploring intriguing quantum phenomena inherent to the topology of spaces. Host: Ar. Abanov

17 Jan 2020, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Michael Kolodrubetz, UT Dallas
Speaker: Michael Kolodrubetz, UT Dallas Title: Floquet systems with quantized drive. Abstract: Time-periodic (Floquet) drive has become a powerful tool to engineer phases of matter, both in equilibrium and far from equilibrium. In this talk, I show that treating drive photons as quantized degrees of freedom, as in cavity QED, leads to interesting phases of coupled light and matter. This is non-trivial even for such “basic” phenomena as many body localization [Ng and MHK, PRL 122, 240402 (2019)], where the localizing interactions compete against global coupling to the quantized cavity mode. I will show how this competition gives rise to unusual phenomena such as an inverted mobility edge, with delocalization at low energies. I then discuss topological versions of the problem, such as the Floquet-Thouless energy pump [MHK et al, PRL 120, 150601 (2018)], where topological pumping naturally occurs by a quantized backaction on the drive. These phases may be realizable experimentally in many body cavity QED and superconducting circuit QED. Host: Ar. Abanov

24 Jan 2020, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Kate Ross, Colorado State
Speaker: Kate Ross, Colorado State Title: Quantum Dimers and Field Induced Bose Einstein Condensation in a Spin-Orbit Coupled Oxide Abstract: The quantum dimer magnet (QDM) is the canonical example of 'quantum magnetism'. This state consists of entangled nearest-neighbor spin dimers and often exhibits a field-induced 'triplon' Bose-Einstein condensate (BEC) phase. I will discuss a new QDM in the strongly spin-orbit coupled, distorted honeycomb-lattice material Yb2Si2O7. Single crystal neutron scattering, specific heat, and ultrasound velocity measurements reveal a gapped singlet zero field ground state with sharp, dispersive excitations. We find a field-induced magnetically ordered phase reminiscent of a BEC phase, with exceptionally low critical fields of Hc1 ~0.4 T and Hc2 ~1.4 T. Using inelastic neutron scattering we observe a Goldstone mode that persists throughout the entire field-induced magnetically ordered phase, suggestive of the spontaneous breaking of U(1) symmetry expected for a triplon BEC. However, in contrast to other well- known cases of this phase, the high-field (H > 1.2T) part of the phase diagram in Yb2Si2O7 is interrupted by an unusual regime signaled by a change inthe field dependence of the ultrasound velocity and net magnetization, as well as the disappearance of a sharp anomaly in the specific heat. These measurements raise the question of how anisotropy in strongly spin-orbit coupled materials modifies the field induced phases of QDMs. Host: Ar. Abanov

31 Jan 2020, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Evan Philip, Stony Brook
Speaker: Evan Philip, Stony Brook Title: Chiral Photocurrents and Terahertz Emission in Dirac/Weyl Semimetals Abstract: I will start with an introduction to Dirac/Weyl semimetals and chiral anomaly. We will then look at a new mechanism for photocurrents in Dirac/Weyl semimetals that relies on the chiral anomaly. I will also discuss terahertz emission from the Weyl semimetal TaAs induced by a near-infrared laser, where Weyl fermions play a central role. We will conclude with remarks on some potential applications of these works. Host: A. Belyanin

7 Feb 2020, 4:00PM | MIST M102
Hosted By: A. Belyanin

Speaker: OPEN Title: Abstract: Host:

14 Feb 2020, 4:00PM | MIST M102

Brad Ramshaw , Cornell (notice the room change!)
Speaker: Brad Ramshaw , Cornell (notice the room change!) Title: TBD Abstract: Host: Ar. Abanov

21 Feb 2020, 4:00PM | MIST M108
Hosted By: Ar. Abanov

Alexei Kitaev, Caltech
Speaker: Alexei Kitaev, Caltech Title: TBA Abstract: Host: V. Pokrovsky

28 Feb 2020, 4:00PM | MIST M102
Hosted By: V. Pokrovsky

APS March Meeting
Speaker: APS March Meeting Title: Abstract: Host:

6 Mar 2020, 4:00PM | Denver, CO

Spring Break
Speaker: Spring Break Title: Abstract: Host:

13 Mar 2020, 4:00PM | Everywhere

Shambhu Ghimire, Stanford
Speaker: Shambhu Ghimire, Stanford Title: TBA Abstract: Host: H. Schuessler

20 Mar 2020, 4:00PM | MIST M102
Hosted By: H. Schuessler

Speaker: OPEN Title: Abstract: Host:

27 Mar 2020, 4:00PM | MIST M102

Physics Festival
Speaker: Physics Festival Title: Abstract: Host:

3 Apr 2020, 4:00PM | MIST M102

Good Friday
Speaker: Good Friday Title: Abstract: Host:

10 Apr 2020, 4:00PM | MIST M102

Peter Armitage, Johns Hopkins University,
Speaker: Peter Armitage, Johns Hopkins University, Title: TBA Abstract: Host: Ar. Abanov

17 Apr 2020, 4:00PM | MIST M102
Hosted By: Ar. Abanov

Speaker: OPEN Title: Abstract: Host:

24 Apr 2020, 4:00PM | MIST M102

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