DC and high-frequency conductivity of the organic metals beta"-(BEDT-TTF)2SF5RSO3 (R = CH2CF2 and CHF)

TL;DR

This study investigates the electrical transport and high-frequency conductivity of organic metals beta"-(BEDT-TTF)2SF5RSO3, revealing superconductivity, charge fluctuations, and anisotropic metallic behavior through dc and microwave measurements.

Contribution

It provides detailed microwave and dc transport data on these organic conductors, highlighting charge fluctuations and anisotropic properties near a charge-order transition.

Findings

Superconductivity observed in beta"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated form.

Charge fluctuations cause microwave resistivity increase below 20 K.

Perpendicular transport shows signs of localization despite metallic behavior.

Abstract

The temperature dependences of the electric-transport properties of the two-dimensional organic conductors beta"-(BEDT-TTF)2SF5CH2CF2SO3, beta"-(d8-BEDT-TTF)2SF5CH2CF2SO3, and beta"-(BEDT-TTF)2SF5CHFSO3 are measured by dc methods in and perpendicular to the highly-conducting plane. Microwave measurements are performed at 24 and 33.5 GHz to probe the high-frequency behavior from room temperature down to 2 K. Superconductivity is observed in beta"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated analogue. Although all the compounds remain metallic down to low-temperatures, they are close to a charge-order transition. This leads to deviations from a simple Drude behavior of the optical conductivity which become obvious already in the microwave range. In beta"-(BEDT-TTF)2SF5CH2CF2SO3, for instance, charge fluctuations cause an increase in microwave resistivity for T < 20 K which is not detected in dc measurements. beta"-(BEDT-TTF)2SF5CHFSO3 exhibits a simple metallic behavior at all frequencies. In the dc transport, however, we observe indications of localization in the perpendicular direction.