Fragile structural transition inMo3Sb7

Abstract

Mo3Sb7 single crystals lightly doped with Cr, Ru, or Te are studied in order to explore the interplay between superconductivity, magnetism, and the cubic-tetragonal structural transition. The structural transition at 53 K is extremely sensitive to Ru or Te substitution which introduce additional electrons, but robust against Cr substitution. No sign of a structure transition was observed in superconducting Mo2.91Ru0.09Sb7 and Mo3Sb6.975Te0.025. In contrast, 3at% Cr doping only slightly suppresses the structural transition to 48 K while leaving no trace of superconductivity above 1.8 K. Analysis of magnetic properties suggests that the interdimer interaction in Mo3Sb7 is near a critical value and essential for the structural transition. All dopants suppress the superconductivity of Mo3Sb7. The tetragonal structure is not necessary for superconductivity.

Competition of superconductivity with the structural transition inMo3Sb7

“…In addition, with a structural transition and spin-gap formation above the superconductivity transition, Mo 3 Sb 7 can be also regarded as an interesting system to explore the quantum criticality with an intimated interplay between lattice instability, magnetism, and superconductivity. 2,3 By utilizing high pressure as a clean tuning knob, we demonstrate in this work the competitive coexistence of superconductivity with the structural transition, which should serve as a constraint when discussing the mechanism of observed superconductivity in Mo 3 Sb 7 .…”

“…2,3 Mo 3 Sb 7 has been known since 1960s as the only compound in the Mo-Sb binary system. 4 The revival of interest in this compound arises from the recent discovery of superconductivity below T c ≈ 2.1 K as well as the promising thermoelectric properties upon proper doping.…”

Multiple superconducting states induced by pressure inMo3Sb7

“…Chemical doping has been exploited previously to study superconductivity in Mo 3 Sb 7 [19,23]. We show here that hydrostatic pressure is a particularly effective tuning mechanism, and we find a second superconducting state with a factor of two greater T c following a pressure-induced first-order phase transition to a higher structural symmetry phase (Fig.…”

“…At ambient pressure, Mo 3 Sb 7 goes superconducting at T c = 2.35 K, with a structural phase transition from high-temperature cubic symmetry to low-temperature tetragonal symmetry at T S = 53 K [9][10][11]. Whether this structural transition is magnetically driven is still an open question [9][10][11]19], although no long-range spin order has been observed to date through either neutron or x-ray magnetic diffraction [11]. Magnetic susceptibility measurements give one S=1/2 local moment per Mo site from fits to a Curie-Weiss law at high temperature [9][10][11], with spin gap behavior at low temperature that suggests a spinPeierls transition at T S [10,11].…”

“…A valence bond crystal also has been suggested as a possible ground state amid strong spin frustration [9]. The superconductivity has been claimed to be s-wave at ambient pressure [20][21][22], but the possibility of unusual magnetic phases at low temperature [9][10][11]19] have raised the question about the role of spin coupling.…”