Competition of superconductivity with the structural transition inMo3Sb7

Abstract

Prior to the superconducting transition at T c ≈ 2.3 K, Mo 3 Sb 7 undergoes a symmetry-lowering, cubic-to-tetragonal structural transition at T s = 53 K. We have monitored the pressure dependence of these two transitions by measuring the resistivity of Mo 3 Sb 7 single crystals under various hydrostatic pressures up to 15 GPa. The application of external pressure enhances T c but suppresses T s until P c ≈ 10 GPa, above which a pressure-induced first order structural transition takes place and is manifested by the phase coexistence in the pressure range 8 ≤ P ≤ 12 GPa. The cubic phase above 12 GPa is also found to be superconducting with a higher T c ≈ 6 K that decreases slightly with further increasing pressure. The variations with pressure of T c and T s satisfy the Bilbro-McMillan equation, i.e. T c n T s 1-n = constant, thus suggesting the competition of superconductivity with the structural transition that has been proposed to be accompanied with a spin-gap formation at T s . This scenario is supported by our first-principles calculations which suggest the possible importance of magnetism that competes with the superconductivity in Mo 3 Sb 7 .

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Multiple superconducting states induced by pressure inMo3Sb7

“…The pressure evolution of superconductivity in Mo 3 Sb 7 was measured using ac magnetic susceptibility ( Turning to structural information, the phase boundary T S (P) was tracked by macroscopic probes such as the electrical resistivity [27], where T S (P) is suppressed by increasing pressure (Figs. 1), but only slowly (~2.5K/GPa), remaining well above zero out to 12 GPa.…”

“…We therefore believe that the main influence on T c should come from the electron-phonon coupling constant λ, with λ dependent on both electronic structure and the phonon dispersion spectrum [39]. The smoothly varying resistivity under pressure [27] indicates a continuously evolving electronic structure, consistent with estimated small difference between the tetragonal and cubic structures by theoretical calculation at ambient pressure [38]. Hence the origin of the doubled T c most likely arises from details of the symmetry-dependent phonon dispersion [39].…”