Condensed Matter Physics

Professor Venkat Chandrasekhar, Northwestern University 

Title: Superconductivity, Magnetism, Anisotropy, Spin-Orbit Interactions and Memory: The Remarkable Properties of the Conducting Gas at (111) SrTiO3 Based Interfaces

Abstract: The 2D conducting gas that forms at the interface between the two insulators LaAlO3 (LAO) and SrTiO3 (STO) has garnered a lot of attention due to wide variety of physical phenomena that it exhibits, including strong spin–orbit coupling, superconductivity, magnetism, and localization effects, among others. Most of the experimental and theoretical work so far has been on LAO/STO interfaces grown in the (001) crystal orientation, in which the system has rectangular symmetry at the interface. More recently, interest has focused on LAO/STO interface grown in the (111) crystal orientation, in which the interface has hexagonal symmetry, similar to graphene and transition-metal-dichalcogenides, raising the possibility of topological effects. As with the (001) interface structures, we find that the system exhibits both superconductivity and magnetism coexisting at the same interface. Unlike the (001) interface, the (111) interface is highly anisotropic, showing different characteristics along different crystal directions in all its properties, including longitudinal resistivity, Hall effect, quantum capacitance, superconductivity and magnetism. The anisotropy is a signature of an electronic nematic state that onsets below ~20 K. We observe an unusual memory effect in the superconducting state: the system remembers the gate voltage at which it is cooled through the superconducting transition. I will also discuss more recent results on (111) LSAT/STO heterostructures that indicate magnetism whose origin lies in a gate-tunable spin-orbit interaction.

Host: Jim Sauls


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Erhai Zhao: TBA

May 3, 2018, 4:00 PM - 5:30 PM

Professor Erhai Zhao, Geroge Mason University 

Title: TBA

Abstract: TBA

Host: Jim Sauls


Dr. Leo Li, Columbia University

Title: Graphene Double-layers: Exciton condensate and beyond

Abstract: A graphene double layer heterostructure is achieved by bringing two monolayer graphene in close vicinity, separated by an insulating hexagonal boron nitride (hBN) crystal that is ~2nm thick. The strong interlayer Coulomb coupling makes such structure an ideal platform to study 2-component ground states in the quantum Hall effect regime, including, but not limited to, exciton condensate. In this talk, I will present results from graphene double layer in corbino geometry, where transport measurements directly probe bulk ground state without interference of edge channels. The combination of parallel flow and counterflow measurements offer insights into the pairing mechanism and ground state order of the exciton condensate. Additionally, access to magnetic field up to 31T lead to the first experimental observation of an interlayer coherent fermi sea at ⅓ filling in each layer and its associated 2-component fractional quantum Hall sequence. I will explore the 2-dimensional phase space of graphene double layer, and the intricate landscape of novel states of matter such as exciton superfluid at fractional filling.

Host: Bill Halperin


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TBA: TBA

May 17, 2018, 4:00 PM - 5:30 PM

TBA

Title: TBA

Abstract: TBA

Host: TBA


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Professor Arun Paramekanti: TBA

May 24, 2018, 4:00 PM - 5:30 PM

Professor Arun Paramekanti, University of Toronto

Title: TBA

Abstract: TBA

Host: Venkat Chandrasekhar


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TBA: TBA

June 7, 2018, 4:00 PM - 5:30 PM

TBA

Title: TBA

Abstract: TBA

Host: TBA