Abstract
(Ca0.5Sr0.5)3Rh4Sn13 is a member of the substitution series (CaxSr1–x)3Rh4Sn13 which has recently been argued to feature a structural quantum critical point at xc = 0.9. In the stoichiometric compound Sr3Rh4Sn13, the structural transition at T* ≈ 138 K has been shown to be second-order. Moving towards xc, we examine the character of the structural transition in (Ca0.5Sr0.5)3Rh4Sn13 (i.e. x = 0.5, T* ≈ 55 K) using electrical resistivity, heat capacity and X-ray scattering. The absence of the thermal hysteresis in specific heat around T*, and the continuous evolution of the superlattice reflection detected by X-ray diffraction are consistent with the scenario that the structural transition associated with a modulation vector q = (0.5 0.5 0) in (Ca0.5Sr0.5)3Rh4Sn13 remains second-order on approaching the quantum critical point.
Highlights
Sr3 Rh4 Sn13 is a conventional s-wave superconductor with a critical transition temperature (Tc )of 4.7 K [1, 2, 3]
In addition to the superconducting transition at low temperature, the structural transition at T ∗ ∼ 55 K can be identified as the hump in the electrical resistivity
At 20.6 kbar, the T ∗ feature is no longer visible in the electrical resistivity. This confirms the trend that pressure moves the system towards the right hand side of the phase diagram
Summary
Sr3 Rh4 Sn13 is a conventional s-wave superconductor with a critical transition temperature (Tc ). In addition to the superconducting transition, another second-order phase transition takes place at T ∗ =138 K This high temperature transition has been established to be a structural phase transition between the P m3̄n and I 4̄3d space groups above and below T ∗ , respectively. In the vicinity of xc , several important observations are noted: (a) Debye temperature is a minimum, (b) Tc is a maximum, and (c) strong-coupling superconductivity can be stabilized.
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