Spring 2020

POSTPONED: Femto-magnetism meets spintronics: Towards integrated magneto-photonics

Bert Koopmans
Monday, March 30, 2020 - 4:00pm

Novel schemes for optically controlling ferromagnetic order at a femtosecond time scale receive great scientific interest. In the strongly non-equilibrium regime, it has become possible not only to quench magnetic order, but even to deterministically switch the magnetic state by a single femtosecond laser pulses. Moreover, it has been shown that pulsed laser excitation can induce spin currents over several to tens of nanometers. This development triggered a merge of the fields of ‘femto-magnetism’ and spintronics – opening up a fascinating playground for novel physical phenomena. In this...

'Dirty' Quantum Magnets

Itamar Kimchi
Thursday, January 30, 2020 - 3:30pm

Dr. Itamar Kimchi is currently an NRC postdoctoral fellow at JILA, the joint institute of NIST and the Department of Physics at the University of Colorado Boulder

Abstract: Studying quantum entanglement over the past decade has allowed us to make remarkable theoretical progress in understanding correlated many-body quantum systems. However in real materials electrons experience spatially random heterogeneities ("dirt") whose theoretical treatment, including strong correlations, has been a challenge. I will describe how synthesizing ideas from quantum information theory, statistical...

Guiding Principles for Engineering Quantum Matter far from Equilibrium

Martin Claassen
Thursday, January 23, 2020 - 3:30pm

One of the most fascinating aspects of non-equilibrium physics is that a macroscopic quantum system pushed out of equilibrium can exhibit markedly different dynamics when probed on different time scales. Pioneered in time-resolved condensed matter experiments and ultracold atoms, the idea to use external driving such as strong optical pulses holds promise to exceed the limitations set by chemistry and push materials into non-equilibrium states with novel or useful properties. However, a characterization of thermalization, order and dynamics far from equilibrium remains a fundamental...

The Sounds of Quantum Fermi Fluids

Inti Sodemann
Monday, February 3, 2020 - 3:30pm

Ordinary classical fluids have a single type of sound waves consisting of longitudinal compressional oscillations of the density. Solids, on the other hand, have also transverse or shear sound waves because of their non-zero restoring force to shear deformations. In this talk, I will illustrate that quantum fermi liquids can radically deviate from this paradigm by developing a sharp collective transverse or shear sound wave when their interactions increase beyond a threshold, even though their ground state remains in a liquid state without any form of proper static crystalline order. I...

Topology and correlations in two-dimensional systems

Mathias Scheurer
Monday, January 13, 2020 - 3:30pm

Mathias Scheurer is a postdoctoral fellow working on theoretical condensed matter in Prof. Subir Sachdev's group at Harvard University.

Abstract: Two-dimensional (2D) systems have become a very active field of research due to their particularly rich physics. As we know from classical statistical mechanics, 2D systems are special as they are situated right at the lower critical dimension and, as such, just incapable of spontaneously breaking a continuous symmetry at finite temperature. Nonetheless, finite-temperature phase transitions are possible; these are, however, not...

The Search for Topological Phases of Matter

Ashley Cook
Thursday, January 9, 2020 - 3:30pm

Ashley Cook is a postdoctoral researcher in condensed matter theory in the group of Prof. Joel Moore at UC Berkeley.

Abstract: In our daily lives, we encounter phases of matter distinguished by the symmetries they break, such as steam and ice. Such phases are well-understood with very established theory of Ginzburg and Landau, suggesting the work to characterize and understand phases of matter might be close to completion. In the 1980's, however, physicists were confronted with the integer and fractional quantum Hall effects, phases of matter that cannot be...

Josephson Detection of Multiband Effects in Superconductors

James Williams
Thursday, January 16, 2020 - 4:00pm

The study of unconventional superconducting materials remains an active frontier of condensed matter physics. Exotic superconductivity, such as high TC, topological, and heavy-fermion superconductors, often rely on phase sensitive measurements to determine the underlying pairing and/or the nature of novel excitations. In this talk I will detail the use of Josephson effect to detect novel properties of two multiband superconducting systems: NbSe2 [1] and SnTe [2]. Focus will primarily be given modification of conventional Josephson effects due to the loss of time...