Condensed Matter Seminars

Sliced Basis Set Approach to Quantum Chemistry with DMRG

Speaker: 
Miles Stoudenmire, UC Irvine
Event Date and Time: 
Thu, 2017-01-26 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Ian Affleck

Though the density matrix renormalization group (DMRG) is a powerful technique for strongly correlated problems in quantum chemistry, it is not without drawbacks. I will describe a new method for applying DMRG to quasi-1d chemical systems combining a grid approximation of the continuum along one direction with a basis set approximation along the other two directions. Combined with techniques for compressing the long-range interactions, this setup allows DMRG to scale much better for chemistry applications, allowing us to tackle long chains of atoms with modest computing resources.

'Ultrafast Optical Control of Complex Quantum Materials

Speaker: 
Stefan Kaiser, 4th Physics Institute, University of Stuttgart and Max-Planck Institute for Solid State Research
Event Date and Time: 
Thu, 2017-01-12 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Sarah Burke
Intended Audience: 
Graduate

It is well known fact that various phase transitions in condensed matter can by triggered by external parameters such as temperature, pressure, electric field or magnetic field. Finding systems that show phase transitions triggered by external stimulation of light became a particular interesting field of research.

Symmetries in anyon systems

Speaker: 
Fiona Burnell, School of Physics and Astronomy, University of Minnesota
Event Date and Time: 
Thu, 2017-01-05 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Marcel Franz
Intended Audience: 
Graduate

The past decade has seen a number of advances in our understanding of how phases of matter can be distinguished by phenomena other than spontaneous symmetry breaking, notably through global topological properties, such as emergent quasiparticles with fractional statistics known as anyons, or symmetry-protected gapless boundary states.  A particularly rich set of possibilities comes from combining these two, and studying the different possible ways that unbroken symmetries can act on systems of anyons.  I will explore several ways that symmetry can act in anyon systems, and show how studying

Competition of Topological and Nematic Phases in the Two-dimensional Electron Gas

Speaker: 
Gábor Csáthy, Department of Physics and Astronomy and the Birck Nanotechnology Center, Purdue University
Event Date and Time: 
Thu, 2016-12-01 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Joshua Folk
Intended Audience: 
Graduate

The two-dimensional electron gas is a prototypical strongly correlated system which, over the years, has contributed to the development of novel concepts in condensed matter physics such as fractional charge, composite fermions, edge states, Pfaffian correlations, non-Abelian statistics, and topological order. The two-dimensional electron gas hosted in GaAs/AlGaAs heterostructures has a particularly rich set of ground states. Well-known examples are the fractional quantum Hall states and various exotic electronic solids.

Josephson Currents Induced by the Witten Effect

Speaker: 
Jeroen van den Brink, Institute for Theoretical Solid State Physics, IFW Dresden, Germany
Event Date and Time: 
Thu, 2016-11-24 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Mona Berciu
Intended Audience: 
Graduate

We reveal the existence of a new type of topological Josephson effect involving type II superconductors and three-dimensional topological insulators as tunnel junctions. We predict that vortex lines induce a variant of the Witten effect that is the consequence of the axion electromagnetic response of the topological insulator: at the interface of the junction each flux quantum attains a fractional electrical charge of e/4.

Superfluid density and microwave conductivity of FeSe superconductor

Speaker: 
David Broun, Department of Physics, Simon Fraser University
Event Date and Time: 
Thu, 2016-11-17 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Doug Bonn
Intended Audience: 
Graduate

FeSe is an iron-based superconductor of immense current interest due to the large enhancements of Tc that occur when it is pressurized or grown as a single layer on an insulating substrate.  In collaboration with the UBC superconductivity group, we have carried out precision measurements of the superconducting electrodynamics of bulk material, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K.

Macroscopic character of composite high temperature superconducting wires and enhancement of superconductivity by magnetic field

Speaker: 
Boris Spivak, University of Washington
Event Date and Time: 
Thu, 2016-11-10 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Philip Stamp

d-wave symmetry of the superconducting order in the cuprate high temperature superconductors is a well established fact, and one which identifies them as unconventional. However, in macroscopic contexts including many potential applications (i.e. superconducting wires) the material is a composite of randomly oriented superconducting grains in a metallic matrix, in which Josephson coupling between grains mediates the onset of long-range phase coherence.

Driven Dirac Materials

Speaker: 
Alexander Balatsky (Nordita and Los Alamos National Laboratory)
Event Date and Time: 
Fri, 2016-11-04 12:00 - 13:00
Location: 
Hennings 318
Local Contact: 
Marcel Franz
Intended Audience: 
Graduate

Recent pump-probe experiments demonstrate the possibility that Dirac materials (DMs) may be driven into transient excited states describable by the state with two separate inverted occupancies, one for

Magnetism meets topology: Quantum anomalous Hall effect and Chiral spin liquids

Speaker: 
Arun Paramekanti, University of Toronto
Event Date and Time: 
Thu, 2016-10-20 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
Ian Affleck

First, I will discuss recent developments in the field of oxide heterostructures, and present our proposal to realize half-metallic Chern bands and a high Tc quantized anomalous Hall effect in mixed 3d/5d oxides. A key component of this proposal involves an orbital analogue of the Rashba effect which may have broader implications in orbitally degenerate oxides.

Cooper like pairing induced by electron ionic polarizability

Speaker: 
Yizhak Yacoby, Hebrew University of Jerusalem
Event Date and Time: 
Thu, 2016-09-22 14:00 - 15:00
Location: 
Hennings 318
Local Contact: 
George Sawatzky

Using the fact that the electron ionic polarizability response time is practically instantaneous we show that a charge carrier induces large attractive potential to a second carrier in small pockets in the two particle position space. Taking into account the inter-carrier repulsion and the kinetic energy needed in order to confine the carriers to the attractive potential pockets we find that the pairing energy is of the order of the energies seen in high Tc superconductors.

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