Vortex dynamics in UBe13

Recently, an anomalous vortex behavior was reported on the low-temperature superconducting (sc) phase of U1-xThxBe13 with x 0: 0275: At T-c2; the second sc transition, vortex creep is reduced sharply by about three orders of magnitude to undetectable low levels [Phys. Rev. B 65 (2002) 144519]. This lack of creep in the low-temperature phase has been interpreted by Sigrist and Agterberg as due to strongly pinned vortices with fractional flux quanta, trapped in walls separating degenerate superconducting domains [Prog. Theor. Phys. 101 (1999) 965]. We present here an investigation of flux creep in UBe13: We then compare these data with previous results from the literature on specific heat and thermal expansion on the same sample, in order to reach a better understanding of the phase diagram of this unconventional superconductor. (C) 2003Elsevier B.V. All rights reserved.