Samuel Lederer

Ising nematic quantum critical point in a metal: a Monte Carlo study

The Ising nematic quantum critical point (QCP) associated with the zero temperature transition from a symmetric to a nematic {\it metal} is an exemplar of metallic quantum criticality. We have carried out a minus sign-free quantum Monte Carlo study of this QCP for a two dimensional lattice model with sizes up to

Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point

24\times 24

Non-topological nature of the edge current in a chiral

sites. The system remains non-superconducting down to the lowest accessible temperatures. The results exhibit critical scaling behavior over the accessible ranges of temperature, (imaginary) time, and distance. This scaling behavior has remarkable similarities with recently measured properties of the Fe-based superconductors proximate to their putative nematic QCP.

p

Significance It has been conjectured that many properties of highly correlated materials, including high-temperature superconductivity, may arise from proximity to a metallic quantum critical point. However, the nature of quantum critical phenomena in metals is incompletely understood. Using numerically exact quantum Monte Carlo methods, we simulated a model that can be tuned through a metallic quantum critical point and observed behaviors that are strikingly reminiscent of experiments. Among these phenomena are high-temperature superconductivity, non-Fermi liquid behavior of the electron Green function, and “bad metal” behavior of the electrical conductivity. Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin 12 itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting Tc enclosing the nematic quantum critical point. For temperatures above Tc, we see strikingly non-Fermi liquid behavior, including a “nodal–antinodal dichotomy” reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with “bad metal” phenomenology.

-wave superconductor

The edges of time reversal symmetry breaking topological superconductors support chiral Majorana bound states as well as spontaneous charge currents. The Majorana modes are a robust, topological property, but the charge currents are non-topological--and therefore sensitive to microscopic details--even if we neglect Meissner screening. We give insight into the non-topological nature of edge currents in chiral p-wave superconductors using a variety of theoretical techniques, including lattice Bogoliubov-de Gennes equations, the quasiclassical approximation, and the gradient expansion, and describe those special cases where edge currents do have a topological character. While edge currents are not quantized, they are generically large, but can be substantially reduced for a sufficiently anisotropic gap function, a scenario of possible relevance for the putative chiral p-wave superconductor Sr

Suppression of spontaneous currents in Sr 2 RuO 4 by surface disorder

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Observable NMR signal from circulating current order in YBCO

RuO

Enhancement of Superconductivity near a Nematic Quantum Critical Point

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Evidence from tunneling spectroscopy for a quasi-one-dimensional origin of superconductivity in Sr2RuO4

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Ising Nematic Quantum Critical Point in a Metal: A Monte Carlo Study

A major challenge to the chiral