The impact of nuclear magnetism on superconductivity in a metal with nuclear electric quadrupole splitting: Indium

We report the first investigation of the impact of nuclear magnetism on. su perconductivity in the tetragonal metal indium. We have measured the superc onducting critical field B-c(T) and in its vicinity the nuclear magnetic he at capacity at ultralow temperatures, 170 muK less than or equal to T less than or equal to 200 MK. We compare the measured quantities with calculatio ns which consider the nuclear magnetic Zeeman and the dominating nuclear el ectric quadrupole interaction in indium. The heat capacity data support the occurence of a positive sign of the electrical field gradient at nuclear s ites and in consequence the existence of a nuclear low spin ground state. S urprisingly, at lowest investigated temperatures, 170 muK less than or equa l to T less than or equal to 1 mK. the reduction of the critical field Delt aB(c)(T) clearly exceeds the size of the calculated magnetization mu M-0(B- c, T) which is limited by the nuclear low spin ground state. In all other m aterials the interplay of nuclear magnetism and superconductivity has been. studied so far (Al, AuAl2, AuIn2, Rh, and Sn), the bare nuclear magnetizat ion appeared as an upper limit of the reduction of the critical field.