Pressure-induced symmetry lowering in NbSnsuperconductor.

Cubic-3NbSnsuperconductor (∼ 16 K) was found to exhibit tetragonal instabilities at the superconducting state (= 10 K). These instabilities are manifested through the appearance of reflections which are forbidden in the-3symmetry but are compatible with the4/structure which is observed in the NbSnsystem for higher Sn content at temperatures lower than ∼43 K. Nevertheless, the low-temperature structure of NbSnremains metrically fully cubic, as concluded from single crystal synchrotron radiation diffraction experiments. Subsequent application of external pressure amplifies the observed instabilities with a resulting pseudo-cubic-tetragonal transformation at= 3 GPa at 10 K and this transition is energy driven, as concluded fromcalculations. The electronic structures of the corresponding phases are virtually identical and, therefore, the pseudo-cubic-tetragonal transformation does not influence significantly the underlying electronic interactions. Consequently, no anomalies in the behavior of the critical temperature,, are expected at this pressure. However, anomalies in the upper critical field are anticipated during this transition, in analogy to the corresponding behavior observed during the cubic-tetragonal transformation in NbSninduced by increase in Sn content. Therefore targeted changes in composition could be used to enhance upper critical field of NbSnfor specific extreme conditions of temperature and pressure.