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# Condensed Matter

This series consists of talks in the area of Condensed Matter.

## Seminar Series Events/Videos

nov 19 2019 - 3:30pm
Room #: 294
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nov 21 2019 - 3:30pm
Room #: 301
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nov 22 2019 - 1:30pm
Room #: 400
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nov 25 2019 - 1:30pm
Room #: 405
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## Dirty Quantum Criticality

Mardi nov 12, 2019
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## Numerical approach to infrared conformality and associated dualities in 2+1 dimensions

Mardi nov 05, 2019
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QFTs in 2+1 dimensions are powerful systems to understand the emergence of mass-gap and particle spectrum in QCD-like theories that describe our 3+1 dimensional world. Recently, these 2+1 dimensional systems have attracted even more attention due to conjectured dualities between seemingly very different theories and due to their applications to condensed matter systems. In this talk, I will describe our numerical investigations of the infrared behaviors of 2+1 dimensional U(1) and SU(N) gauge theories coupled to many favors of massless fermions using lattice regularization.

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## Hydrodynamics and (Pre)Thermalization in Floquet Systems

Vendredi nov 01, 2019
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A tremendous amount of recent attention has focused on characterizing the dynamical properties of periodically driven many-body systems. Here, we use a novel numerical tool termed ‘density matrix truncation’ (DMT) to investigate the long-time dynamics of large-scale Floquet systems. By implementing a spatially inhomogeneous drive to a 1D quantum chain, we demonstrate that an interplay between Floquet heating and diffusive transport is crucial to understanding the system’s dynamics.

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## Symmetry indicators for topological materials

Mardi oct 22, 2019
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Many free-fermion topological phases can be diagnosed by analyzing a suitable collection of symmetry data. While the Fu-Kane parity criterion for topological insulators is an early example, the systematic generalization to cover all possible crystalline symmetries and their associated topological phases has only recently been achieved.

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## A Universal Operator Growth Hypothesis

Mardi oct 15, 2019
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Thanks to the Lanczos algorithm, the Hamiltonian dynamics of any operator can be written as a hopping problem on a semi-infinite one-dimensional chain. Our hypothesis states that the hopping strength grows linearly down the chain, with a universal growth rate $\alpha$ that is an intrinsic property of the system. This leads to an exponential motion of the operator down the chain, capturing the irreversible process of simple operators inevitably evolving into complex ones. This exponential growth exists for generic quantum systems, even away from large-$N$ or semiclassical limits.

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## Long-lived interacting phases of matter protected by multiple time-translation symmetries in quasiperiodically driven systems

Mardi oct 08, 2019
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The discrete time-translation symmetry of a periodically-driven (Floquet) system allows for the existence of novel, nonequilibrium interacting phases of matter. A well-known example is the discrete time crystal, a phase characterized by the spontaneous breaking of this time-translation symmetry.

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## Some aspects of the complex SYK model

Mardi oct 01, 2019
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Adding the global U(1) symmetry to the SYK model is a simple and fun exercise. I would like to explain how to obtain the charge and zero temperature entropy formulas solely from the IR parameters of the model. In particular, I will mention a free fermion interpretation of the zero temperature entropy. Work in progress with Kitaev, Sachdev, and Tarnopolsky.

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## Bosonization and the shear sound of metals

Mardi sep 24, 2019
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We will review the bosonization approach to Fermi liquids in dimensions above one. We will use this to study a sharp change in the neutral excitation spectrum of fermi liquids that occurs beyond a critical interaction strength whereby an unconventional collective mode exits the particle-hole continuum. This mode is a collective shear wave that features purely transverse current oscillations, in analogy to the transverse sound of crystals. Because it is hard to “see" due to its transversal nature, the shear sound might be already “hiding`' in several metals.

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## Entanglement entropy, quasiparticle fluctuations, and 1D thermal entropy in topological phases

Mardi sep 17, 2019
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Entanglement entropy in topologically ordered matter phases has been computed extensively using various methods. In this talk, we study the entanglement entropy of 2D topological phases from the perspective of quasiparticle fluctuations. In this picture, the entanglement spectrum of a topologically ordered system encodes the quasiparticle fluctuations of the system, and the entanglement entropy measures the maximal quasiparticle fluctuations on the entanglement boundary.

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## A solvable model for magnetic skyrmions

Vendredi sep 13, 2019
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Magnetic skyrmions are topological solitons which occur in a large class of ferromagnetic materials and which  are currently attracting much attention, not least because of their potential use for  low-energy magnetic information storage and manipulation. The talk is about an integrable model for magnetic skyrmions, introduced in a recent paper (arxiv:1812.07268) and generalised in  arxiv:1905.06285.

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