Unexpectedly wide reversible vortex region in $\beta$-pyrochlore RbOs$_{2}$O$_{6}$

TL;DR

This study reveals that RbOs₂O₆ exhibits an unusually wide reversible vortex region in its phase diagram, likely due to intrinsically low bulk pinning, contrasting with typical low-temperature superconductors.

Contribution

It demonstrates that low bulk pinning in β-pyrochlore superconductors leads to an unexpectedly wide reversible vortex region, challenging conventional understanding of vortex dynamics.

Findings

Reversible vortex region extends up to ~0.3 Hc2(T)

Thermal fluctuations are limited with Ginzburg number Gi = 5×10⁻⁷

Low quenched disorder correlates with wide reversible region

Abstract

We study the extent of the reversible region in the vortex phase diagram of recently available RbOs$_2$O$_6$ single crystals \cite{Rogacki08a} by means of bulk magnetization measurements. We found that the irreversible magnetic response sets in at a field $H_{\rm irr}(T) \sim 0.3 H_{\rm c2}(T)$ for $0.5 \lesssim T/T_{\rm c} \lesssim 0.8$, yielding a reversible vortex region that is uncommonly wide in comparison with typical low-$T_{\rm c}$ materials. The relevance of thermal fluctuations is limited since we estimate a Ginzburg number $G_{\rm i} = 5 \times 10^{-7}$. However, the relevance of quenched disorder is unconventionally low since the critical-current density ratio at low fields and temperatures is of the order of that found in high-T$_{\rm c}$'s. We therefore conclude that an intrinsically low bulk pinning magnitude favors the existence of an unexpectedly wide reversible vortex region that seems to be generic to $\beta$-pyrochlores.