University of Connecticut

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Condensed Matter Physics Seminar

Friday, March 1, 2019
2:30pm – 3:30pm

Storrs Campus

Dr. Vladimir Juricic, Nordic Institute for Theoretical Physics

Interacting spin-1/2 and spin-3/2 nodal fermions: Quantum criticality and transport

Theoretical proposals and experimental realizations of the condensed matter systems, such as topological insulators, Weyl and Dirac semimetals, displaying emergent pseudorelativistic nodal quasiparticles, have triggered a surge of activity in understanding their stability against interactions and disorder. This also motivated exploration of their universal responses, such as optical conductivity.

I will first discuss the quantum critical theory of an interacting nodal Fermi liquid of quasirelativistic pseudospin-3/2 fermions featuring a noninteracting birefringent spectrum with two distinct Fermi velocities [1]. As I will show using perturbative field-theoretical renormalization group analysis, when such quasiparticles interact via either the long-range Coulomb interaction or its short range component (responsible for spontaneous symmetry breaking), in the quantum critical regime, in two dimensions, the system is, respectively, described by a marginal Fermi liquid (featuring interaction-driven log-corrections to observables) or a non-Fermi liquid of relativistic spin-1/2 fermions, and is always a marginal Fermi liquid in three dimensions. I will also discuss our conjecture that critical spin-1/2 excitations represent a superuniversal description of the entire family of interacting quasirelativistic fermions.

In the second part of the talk, I will consider the quantum transport close to a relativistic quantum critical point, separating two-dimensional massless Dirac fermions from a fully gapped insulator or superconductor. In particular, I will consider the scaling of optical conductivity in the (high-frequency) collisionless regime (ω ≫ T) [2]. Close to such a critical point, gapless fermionic and bosonic excitations are strongly coupled, which inside the critical regime leads to a universal suppression of the interband optical conductivity as well as of the Drude peak. These results are obtained by performing the leading order 1/Nf- and ϵ-expansions, where Nf counts the fermion flavor number and ϵ is the distance from the upper-critical three spatial dimensions in the problem.

[1] B. Roy, M. P. Kennett, K. Yang & V. J., PRL 121, 157602 (2018).

[2] B. Roy & V. J., PRL 121, 137601 (2018).


Prof. A. Balatsky

Physics Department (primary)

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