Low temperature vortex liquid states induced by quantum fluctuations in the quasi two dimensional organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}

TL;DR

This paper investigates quantum fluctuation-induced vortex liquid states in a layered organic superconductor at very low temperatures, revealing a novel quantum vortex slush state characterized by finite resistivity and non-linear transport behavior.

Contribution

It provides experimental evidence for a quantum vortex slush state induced by quantum fluctuations, distinct from thermal vortex liquids, in a quasi-two-dimensional organic superconductor.

Findings

Finite resistivity persists down to 100 mK in the vortex state.

Identification of a quantum vortex liquid state driven by quantum fluctuations.

Observation of non-linear resistivity behavior at high current densities.

Abstract

We report the transport properties in the vortex liquid states induced by quantum fluctuations at low temperature in the layered organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}. A steep drop of the resistivity observed below about 1 K separates the liquid state into two regions. In the low resistance state at lower temperature, a finite resistivity with weak temperature dependence persists down to 100 mK at least. The finite resistivity in the vortex state at T ~= 0 K indicates the realization of quantum vortex liquid assisted by the strong quantum fluctuations instead of the thermal one. A possible origin for separating these liquid states is a remnant vortex melting line at the original position, which is obscured and suppressed by the quantum fluctuations. A non-linear behavior of the in-plane resistivity appears at large current density in only the low resistance state, but not in another vortex liquid state at higher temperature, where the thermal fluctuations are dominant. The transport properties in the low resistance state are well understood in the vortex slush concept with a short-range order of vortices. Thus the low resistance state below 1 K is considered to be a novel quantum vortex slush state.