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CMTC Talks
CMTC talks are held in room 4402 Atlantic Building unless an alternate location is indicated

Spring 2020

January 16, Thursday, 2 pm
Fengcheng Wu (CMTC), practice talk for a job interview
Symmetry, Topology, and Many-Body Interactions in Moiré Systems
Van der Waals bilayers with small differences in the lattice constants or orientations of the individual layers have long-period Moiré patterns, which provide vast new opportunities to control material properties. In this talk, I will present our work on Moiré pattern physics that arise from an interplay of symmetry, topology and many-body interactions. First, I will describe our theoretical proposal of using twisted bilayer transition metal dichalcogenides as quantum simulators of Hubbard model [1, 2], and discuss recent experimental realizations. Then I will focus on twisted bilayer graphene (TBG) and show how the interplay between many-body interactions and Bloch band symmetry of TBG can lead to unconventional superconductivity [3, 4]. Finally, I will discuss quantum anomalous Hall insulators in TBG and demonstrate their stability against spin/valley magnon excitations [5]. I will describe the effects of quantum geometry on spin stiffness and show that Berry curvature of Moiré bands helps to stiffen spin magnons.
1. F. Wu, T. Lovorn, E. Tutuc, A. H. MacDonald, Phys. Rev. Lett. 121, 026402 (2018).
2. F. Wu, T. Lovorn, E. Tutuc, I. Martin, A. H. MacDonald, Phys. Rev. Lett. 122, 086402 (2019).
3. F. Wu, A. H. MacDonald, and I. Martin, Phys. Rev. Lett. 121, 257001 (2018).
4. F. Wu, E. Hwang, and S. Das Sarma, Phys. Rev. B 99, 165112 (2019).
5. F. Wu, S. Das Sarma, arXiv:1908.05417 (2019).

February 11, Tuesday, 2:30 pm
Eugene Demler (Harvard), in conjunction with his JQI seminar
Nonlinear optics with collective excitations and photoinduced superconductivity
This talk will review the recent progress in theoretical modeling of nonequilibrium dynamics of electron-phonon systems. There will be an emphasis on understanding experimental observations of photoinduced superconductivity.
Host Jay Sau; last update 2020-1-26 by Victor Yakovenko

March 10, Tuesday, 2 pm
Ronny Thomale (Theoretische Physik I, Universitat Wurzburg), see also his JQI and QMC seminars
The Quest of the Kagome Hubbard Model
Since its (re-)discovery in the second half of the 20th century, the lattice of corner-sharing triangles called kagome has become one of the key domains featuring paradigmatic models for exotic quantum electronic states of matter. Depending on the filling, the Hubbard model on the kagome lattice exhibits several fascinating phases subject to contemporary research in condensed matter physics, ranging from topological spin liquids over correlated Dirac metals and unconventional superconductivity to spin-type and charge-type Peierls phases as well as turbulent hydrodynamic flow. I will discuss recent progress in theory to understand such scenarios of correlated electron systems on the kagome lattice.
Host Jay Sau; last update 2020-3-4 by Victor Yakovenko

March 11, Wednesday, 11 am
Gregory Bentsen (Princeton University), QuICS seminar at CMTC location
Tunable geometry and fast scrambling in nonlocal spin networks
The past decade has seen a dramatic increase in the degree, quality, and sophistication of control over quantum-mechanical interactions available between artificial degrees of freedom in a variety of experimental platforms. The geometrical structure of these interactions, however, remains largely constrained by the underlying rectilinear geometry of three-dimensional Euclidean space. At the same time, there has been growing interest in exploring many-body dynamics in systems, such as the SYK model and tensor network models, for which the interaction structure bears little or no resemblance to Euclidean space. Inspired by these complementary developments, here we study a tunable, nonlocal spin network that can be engineered using cold atoms coupled to an optical cavity. The network exhibits two distinct notions of emergent geometry -- linear and treelike -- that can be accessed using a single tunable parameter. In either of these two extreme limits, we find a succinct description of the resulting dynamics in terms of two distinct metrics on the network, encoding a notion of either linear or treelike distance between spins. Moreover, at the crossover between these two regimes, the spin network becomes highly connected and exhibits signatures of fast scrambling. These observations highlight the essential role played by the geometry of the interaction structure in determining a system's dynamics, and raise prospects for novel studies of nonlocal and highly chaotic quantum dynamics in near-term experiments.
Host Brain Swingle; last update 2020-3-6 by Victor Yakovenko

CMTC Seminar Committee as of 2020-1-19:
Jay Sau, Maissam Barkeshli, Brian Swingle, Yi-Ting Hsu, and Danny Bulmash

For the earlier CMTC talks, see this page