Reaching quantum critical point by adding nonmagnetic disorder in single crystals of (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$ superconductor

Abstract

The quasi-skutterudites (Ca${}_x$Sr${}_{1-x}$)${}_3$(Rh, Ir)${}_4$Sn${}_{13}$ show a rare nonmagnetic quantum critical point associated with the second-order charge-density-wave (CDW) and structural distortion transition extended under the superconducting "dome". So far, the non-thermal tuning parameters for accessing the QCP included changing stoichiometry, pressure, and a magnetic field. Here we add another parameter -- a nonmagnetic point-like disorder induced by 2.5 MeV electron irradiation. The non-Fermi liquid regime was inferred from the analysis of the temperature-dependent resistivity, $\ddot{I}\left(T\right)$, in single crystals of (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$. Starting at compositions below the known QCP concentration of $x_c=0.9$, added disorder resulted in a progressively larger linear term and a reduced quadratic term in $\ddot{I}\left(T\right)$. This behavior is supported by theoretical analysis based on the idea of superconducting fluctuations encompassing the crossover from quantum to thermal regimes. Our results strongly support the concept that the nonmagnetic disorder can drive the system toward the quantum critical regime.