Unconventional Superconductivity in Heavy Fermion UTe2

摘要

We grew single crystals of the recently discovered heavy fermion superconductor UTe2, and measured the resistivity, specific heat and magnetoresistance. Superconductivity (SC) was clearly detected at T-sc = 1.65 K as sharp drop of the resistivity in a high quality sample of RRR = 35. The specific heat shows a large jump at T-sc indicating strong coupling. The large Sommerfeld coefficient, gamma =117 ml K(-2)mol(-1) extrapolated in the normal state and the temperature dependence of C/T below T-sc are the signature of unconventional SC. The discrepancy in the entropy balance at T-sc between SC and normal states points out that hidden features must occur. Surprisingly, a large residual value of the Sommerfeld coefficient seems quite robust (gamma(0)/gamma similar to 0.5). The large upper critical field H-c2 along the three principal axes favors spin-triplet SC. For H parallel to b-axis, our experiments do not reproduce the huge upturn of H-c2 reported previously. This discrepancy may reflect that H-c2 is very sensitive to the sample quality. A new perspective in UTe2 is the proximity of a Kondo semiconducting phase predicted by the LDA band structure calculations.