VORTEX-GLASS TRANSITION IN THE (K,BA)BIO3 CUBIC SUPERCONDUCTOR

We present a detailed characterization of the vortex-glass transition in the cubic (K,Ba)BiO3 superconductor (with critical temperature T(c) similar to 30 K). Combining transport measurements down to 0.3 K and t hird-harmonic susceptibility close to T-c we show that the vortex-glas s transition field can be well fitted by a power law: H(g)similar to(1 -T/T-c)(n) with n similar to 1.5 over three magnetic field decades. In striking contrast with cuprates, this simple behavior holds down to o ur lowest temperature. The E-J characteristics are consistent with the vortex-glass transition for both J parallel to H and J perpendicular to H configurations assuming that, close to Tg, the vortex Line is mak ing an average angle similar to 20 degrees with the external field. Th e vortex-glass correlation length reaches several mu m:in the vicinity of the transition: showing that vortices are correlated over more tha n 200a(0) (where a(0) is the intervortex spacing). The characteristic exponents nu=1.0+/-0.2 and z=5.0+/-0.6 are field independent and do no t depend on the relative orientation of the magnetic field and the cur rent density. [S0163-1829(98)04942-X].