Structural and Superconducting Properties of RbOs2O6 Single Crystals

TL;DR

This study reports the growth, structural analysis, and superconducting properties of RbOs2O6 single crystals, revealing it as a weak-coupling BCS superconductor with specific magnetic and thermodynamic parameters.

Contribution

First detailed characterization of RbOs2O6 single crystals, including structure and superconducting properties, highlighting its weak-coupling BCS nature and field-dependent Ginzburg-Landau parameter.

Findings

Lattice constant a = 10.1242 Å at room temperature.

Ginzburg-Landau parameter κ(0) varies from 22 to 31 with field.

Superconducting gap 2Δ/k_B T_c = 3.2.

Abstract

Single crystals of RbOs2O6 have been grown from Rb2O and Os in sealed quartz ampoules. The crystal structure has been identified at room temperature as cubic with the lattice constant a = 10.1242(12) A. The anisotropy of the tetrahedral and octahedral networks is lower and the displacement parameters of alkali metal atoms are smaller than for KOs2O6, so the "rattling" of the alkali atoms in RbOs2O6 is less pronounced. Superconducting properties of RbOs2O6 in the mixed state have been well described within the London approach and the Ginzburg-Landau parameter kappa(0) = 31 has been derived from the reversible magnetization. This parameter is field dependent and changes at low temperatures from kappa = 22 (low fields) to kappa = 31 at H_{c2}. The thermodynamic critical field H_{c}(0) = 1.3 kOe and the superconducting gap 2delta/k_{B}T_{c} = 3.2 have been estimated. These results together with slightly different H_{c2}(T) dependence obtained for crystals and polycrystalline RbOs2O6 proof evidently that this compound is a weak-coupling BCS-type superconductor close to the dirty limit.