CM Theory Seminar Recordings

The Condensed Matter Theory Seminar is held every Wednesday at 1:25 in the Physics and Nanotechnology Building. Please see the calendar below for our upcoming seminars.

Our full catalogue of recordings is available on FTPI's YouTube Channel @FineTheoryInstitute

2023 | 2022



Patrick A. Lee (Massachusetts Institute of Technology and California Institute of Technology)

Strongly Driven Superconductors: What the Data tell us about Cuprates and Organicx

In the past decade, Cavalleri's group has reported "superconducting-like" behavior up to several times Tc in HiTc cuprates, the organic superconductors and K3C60. I will review some of the data and focus on the first two systems. In collaboration with M. Michael and E. Demler, I undertook a new analysis of the YBCO data. The goal is to find the minimal set of assumptions which can explain the observations. Unlike earlier discussions, we find that intense drive does not enhance the in-plane pair correlation or the inter-bilayer correlation. However, in order to explain the data, short range order within the plane and  correlation between members within the bi-layer are required in the equilibrium state. The implication is that pairing correlation survives up to the pseudogap scale. Therefore the pseudogap is a pairing gap. For the organic superconductor, I will also discuss a proposal with Zhehao Dai that the observed enhanced gap under drive is an induced Mott gap rather than a pairing gap.

Liang Fu (Massachusetts Institute of Technology)

Mott, Chern and Wigner Insulators in Semiconductor Heterostructures

The advent of moire superlattices in van der Waals heterostructures opens a new venue for exploring quantum phases of matter with unprecedented tunability. I will describe various kinds of quantum phases at integer fillings in semiconductor bilayer systems at zero magnetic field, including Mott and Chern insulators at the filling of one charge per unit cell, as well as Wigner solids at higher integer fillings.

**There were technical issues with the video recording of this seminar, so only audio is available.**

Dan Stamper-Kurn (University of California, Berkeley)

Many-body Physics of Atoms in Optical Lattices and Optical Cavities

Ultracold atomic gases allow us to create a variety of many-body quantum systems, which we might regard as synthetic quantum materials. In some of these systems, we encounter many of the properties pertinent to condensed-matter systems. In that vein, I will present experiments on atoms in optical lattices where we test a scaling hypothesis that relates phase transitions occurring in different lattice configurations and examine transport and equilibration of itinerant particles in geometrically frustrated bands. I will also share some results obtained from experiments on atoms placed within optical cavities, where they interact strongly with an optical field. This field can serve both as a precise probe, e.g. allowing us to examine non-equilibrium thermodynamics of a mesoscopic system, and also as a dynamical component within a hybridized atom + matter quantum system. I hope to spark some discussion where we can generate some new ideas on applications of quantum simulation, on feedback-controlled quantum matter, and on phase transitions in open quantum systems.




Erez Berg (Weizmann Institute)

What does the Wiedemann-Franz Law Tell Us About Non-Fermi Liquids?

The Wiedemann-Franz (WF) law, stating that the Lorenz ratio L=κ/Tσ between the electronic thermal and electrical conductivities in a metal approaches a universal constant L_0 at low temperatures, is often taken to be a signature of fermionic Landau quasi-particles. In contrast, we show that various models of weakly disordered non-Fermi liquids, where the fermionic quasi-particles are either marginally defined or ill-defined, also obey the WF law at T→0. Instead, we argue that the behavior of the leading correction to the WF law at low temperature distinguishes different types of strange metals. In particular, in a solvable model of a marginal Fermi liquid, we find that the leading low-temperature deviation of L-L_0 scales as T, in contrast to a Fermi liquid where it is proportional to T^2. Moreover, by invoking a quantum Boltzmann equation approach, we demonstrate that this behavior is generic in a class of marginal- and non-Fermi liquids characterized by a weakly momentum-dependent inelastic scattering rate.