Superinsulator Phase of two - dimensional Superconductors

Using path-integral Quantum Monte Carlo we study the low-temperature phase diagram of a two-dimensional superconductor within a phenomeno-logical model, where vortices have a finite mass and move in a dissipative environment modeled by a Caldeira-Leggett term. The quantum vortex liquid at high magnetic fields exhibits superfluidity and thus corresponds to a superinsulating phase which is characterized by a nonlinear voltage-current law for an infinite system in the absence of pinning. This superinsulating phase is shifted to higher magnetic fields in the presence of dissipation. 1 Quantum fluctuations of vortices play an important role for the low-temperature physics of two-dimensional (2D) superconductors. It has been established that dissipative [1], inertial [2,3], or Hall-type [4] zero point motion is able to melt the vortex lattice at sufficiently high magnetic fields and give way to a quantum vortex liquid phase in principle at T = 0. In the presence of disorder this melting transition is a continuous one and corresponds to the localization or crystallization of Cooper pairs in the theory of the superconductor-insulator transition [5,6]. However, for a system without disorder, the melting of the vortex lattice is discontinuous in (2+1) dimensions [3]. In this letter, using path-integral Quantum Monte Carlo (QMC), we will study a phe-nomenological model where the vortices have a finite mass and move in a dissipative environment , which is modeled by a Caldeira-Leggett term. Both, vortex mass and dissipation are assumed to originate from electronic contributions while the vortices themselves are considered as bosons. For the simulations we focus on the situation where the Magnus force is zero which is appropriate for the case of granular systems or Josephson Junction arrays (JJA) where experiments suggest that the transverse force is very small [7]. The effect of a weak Magnus force will then be discussed afterwards. In a thin film superconductor at high magnetic fields vortices effectively interact logarithmically. So the question arises whether the vortices can form a superfluid or not. We will show using QMC that a 2D system of logarithmically interacting particles indeed exhibits superfluidity at low temperatures and high densities even in the presence of dissipation. [8] This means that the quantum vortex liquid actually corresponds to a superinsulating phase in which an infinitesimal current will cause an infinite voltage in the absence of pinning effects in analogy with sliding charge density waves. This superinsulating phase exhibits a non-linear voltage-current law with non-universal exponent …