Magnetization measurements on single crystals of superconducting Ba_0.6K_0.4BiO₃

Abstract

Extensive measurements of the magnetization of superconducting singlecrystal samples of Bao,6Ko 4Bi03 have been made using superconducting quantum interference device and cantilever force magnetometry at temperatures ranging between 1.3 and 350K and in magnetic fields from near zero to 27T. Hysteresis curves of magnetization versus field allow a determination of the thermodynamic critical field, the reversibility field and the upper critical field as functions of temperature. The lower critical field is measured separately and the Ginzburg-Landau parameter is found to be temperature dependent. All critical fields have higher T = 0 limits than have been previously noted and none of the temperature dependences of the critical fields follows the expected power laws leading to a possible alternative interpretation of the thermodynamic nature of the superconducting transition.f Emaili

Theory of a higher-order phase transition: The superconducting transition inBa0.6K0.4BiOKumar1 2003Phys. Rev. BSelf Cite100120View full textAdd to dashboardCite

“…Kwok et al 28 used this expression to estimate ∆C/T c ≈ 3.75 mJ/mole/K 2 . In the measurements of Hall et al 1,2 , κ apparently diverges near T c as κ ≈ (1 − t) −1 . If we use this temperature dependence, we get ∆C = 0.…”

“…There has been a proposal 1,2 recently that the transition to superconductivity in the cubic, non-copper based, moderate T c (32K) material Ba 0.6 K 0.4 BiO 3 (BKBO) is of order four in the sense proposed by Ehrenfest 3 . The free energy and its first three derivatives are continuous across the phase transition.…”

Phase transition in the diffusion and bootstrap percolation models on regular random and Erdős-Rényi networks

“…Recently, third-order phase transitions were proposed concerning large-N four-dimensional lattice gauge theory [50], spin glass [51], supercritical fluids [52], the domino tilings of an Aztec diamond [53], and constrained Coulomb gas [54]. In some superconducting transitions, thirdorder [55,56] and fourth-order [57,58] phase transitions were suggested. However, there are still controversies about the existence of higher-order phase transitions [59,60].…”

Spatial structures in a generalized Ginzburg-Landau free energy

“…These anomalies, a missing discontinuity in specific heat 12,13 as well as in susceptibility, 5,11 indicate a phase transition of order higher than second. The actual order in BKBO has been determined 5 to be fourth.…”