Possible quantum fluctuations in the vicinity of the quantum critical point of $(\mathbf{Sr},\mathbf{Ca}{)}_3\mathbf{I}{\mathbf{r}}_4\mathbf{S}{\mathbf{n}}_{13}$ revealed by high-energy X-ray diffraction study

Abstract

We explore the evolution of the structural phase transition of $(\mathrm{Sr},\mathrm{Ca}{)}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature $T^{\ast }$ against pressure, which extrapolates to zero at a critical pressure of $\approx 1.79(4)$ GPa. The temperature evolution of the superlattice Bragg peak in $\mathrm{C}{\mathrm{a}}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$ reveals a drastic decrease of the intensity and an increase of the linewidth when $T\to 0$ K and $p\to p_c$. Such anomaly is likely associated to the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of $(\mathrm{Sr},\mathrm{Ca}{)}_3\mathrm{I}{\mathrm{r}}_4\mathrm{S}{\mathrm{n}}_{13}$ thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors.