Quantum vs thermal fluctuations in phase transitions of two-dimensional superconductors

TL;DR

This paper explores how quantum and thermal phase fluctuations influence superconductivity suppression in two-dimensional systems, using quantum Monte Carlo simulations to map phase diagrams and analyze conductivity.

Contribution

It provides a detailed phase diagram of 2D superconductors considering quantum and thermal fluctuations, highlighting the quantum critical point and fluctuation effects on conductivity.

Findings

Critical line ending at a quantum critical point without reentrant behavior

Resistance exhibits two distinct critical behaviors above the critical line

Finite-frequency conductivity indicates quantum phase fluctuation effects

Abstract

We investigate the impact of quantum and thermal phase fluctuations on the suppression of superconducting order in two-dimensional systems. Within the two-dimensional quantum XY model in the phase representation, where on-site interaction terms govern quantum phase fluctuations, we perform extensive path-integral quantum Monte Carlo simulations. The resulting temperature-interaction phase diagram establishes the presence of a well-defined critical line ending at a quantum critical point at vanishing temperature with no indication of reentrant behavior. We further demonstrate that the resistance above the critical line reproduces the two expected different critical behaviors. For stronger interactions, above the quantum critical point, the system exhibits a crossover to an insulating regime at low temperatures. Finally, Monte Carlo calculations of current-current correlation functions enable us to extract the frequency-dependent conductivity in both superconducting and normal regimes, revealing a finite-frequency response that we attribute to quantum phase fluctuations.