Vortex-glass transition in the (K,Ba)BiO3 cubic superconductor

Abstract

We present a detailed characterization of the vortex-glass transition in the cubic (K,Ba)BiO3 superconductor (with critical temperature Tc∼30K). Combining transport measurements down to 0.3K and third-harmonic susceptibility close to Tc we show that the vortex-glass transition field can be well fitted by a power law: Hg∼(1−T/Tc)n with n∼1.5 over three magnetic field decades. In striking contrast with cuprates, this simple behavior holds down to our lowest temperature. The E−J characteristics are consistent with the vortex-glass transition for both J∥H and J⊥H configurations assuming that, close to Tg, the vortex line is making an average angle ∼20° with the external field. The vortex-glass correlation length reaches several μm in the vicinity of the transition, showing that vortices are correlated over more than 200a0 (where a0 is the intervortex spacing). The characteristic exponents ν=1.0±0.2 and z=5.0±0.6 are field independent and do not depend on the relative orientation of the magnetic field and the current density.

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