Upper Critical Magnetic Field of the Heavy-Fermion Superconductor UBe13

Superconductivity and heavy fermions

“…Kondo-lattice UBe13: similarities and differences to the single site physics Heavy fermions are the quaslparticles m a Kondo-lattlce Whereas the single site Kondo problem is well understood m its details by now, attempts to solve the lattice problem have not been particularly successful so far [1] One of the 0304-8853/87/$03 50 O Elsevier Science Publishers (North-Holland Physics Pubhshing Division) questions is whether low and high temperature properties can be described by a smgle scalmg parameter (TK), and to what extent mterstte interactions modify the behavior at the lowest temperatures (Vanishing of resistance ~s an obwous consequence) Here we report two experimental observations pertinent to this question One of the hallmarks of the Kondo effect ts the logarithmic resistance increase upon cooling, which is also seen m the Kondo lathces, w~th the notable exception of UPt~ This resistance can be suppressed by magnetic fields of strength glxH kT~, as we have found in magnetores~stance measurements of UBel3 in fields up to 23 T and from 05 to 25K In the range of overlap our results are m agreement w~th other stu&es, which also found a pronounced decrease of R in magnetic fields [2][3][4][5] Much quant~tatwe insight ts gamed by reahzing that the functional form of R(H) is well described by R(H) calculated for the J --l/2 Coqbhn-Schneffer model [6] the field-reduced variation of the 2J + 1 sublevel populatmn When J ~< 1 this leads to a subhnear magnetlzatmn curve Take, for example, the case of J= 1/2 at H=0 4 H* the resistance has dropped by ~-33%, and the magnetization deviates from hneanty by ~17% [6] We have measured the magnetization of UBe13 with high accuracy in a SQUID magnetometer at T = I 5 K in fields up to 5 T and found no devmtion from hneanty within :L0 2% This is to be contrasted to the expectation from the remstance drop which would give a reduction from hneanty by ~-6% (see fig 1) …”

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…It may come from a two-band Fermi surface topology as in MgB 2 , [35][36][37] or an unconventional superconducting state as in heavy-fermion compound UBe 13 . 38 11,[39][40][41] We notice that no superconductivity was observed up to 13.43 GPa in an earlier pressure study of Cd 3 As 2 single crystal. 42 The reason may be that their sample is slightly different from ours, and pressure higher than 13.43 GPa is needed to induce superconductivity.…”

Heavy fermion behavior in uranium compounds

“…First, the upper critical field has a nearly vertical slope at T~ = 0.9 K ( fig. 6) [19]. The high value of the electrical resistivity at T c (= 100 pf~cm) makes p-wave pairing seem an unlikely possibility in view of the fact that the scattering implied by this large resistivity would destroy the angular momentum of the pairs.…”