Ambient Pressure Structural Quantum Critical Point in the Phase Diagram of (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$

Abstract

The quasi-skutterudite superconductor Sr${}_3$Rh${}_4$Sn${}_{13}$ features a pronounced anomaly in electrical resistivity at $T^{\ast }\sim$138 K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centred around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of $T^{\ast }$ as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., $x_c=0.9$). This establishes (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$ series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures.

5 pages, 4 figures, accepted for publication in Phys. Rev. Lett