Effect of pressure on the superconducting properties of Au substituted PdTe${}_2$ with the CdI${}_2$-type structure

Abstract

Transition metal ditellurides with the CdI${}_2$-type structure are materials with intriguing superconducting and electronic properties as demonstrated by PdTe${}_2$. Gold substituted PdTe${}_2$, Au${}_x$Pd${}_{1-x}$Te${}_2$, adopts the CdI${}_2$-type structure for a Pd content larger than 43 at.\% at room temperature, and in this range enhanced superconductivity with a critical temperature ($T_{\mathrm{c}}$) above 4 K has been reported (Kudo \it{et al}., PRB \bf{93}, 140505, 2016). Here we present the effect of pressure on the structural and superconducting properties of Au${}_x$Pd${}_{1-x}$Te${}_2$ for $x=0.15$, 0.25 and 0.35 with $T_{\mathrm{c}}=2.7$, 4.1, and 4.6 K at 1 atm, respectively. Synchrotron radiation x-ray diffraction shows that the CdI${}_2$-type structure remains stable up to 8 GPa for all three compositions and that they have almost the same volume compressibility. Heat capacity measurements show that Au substituted PdTe${}_2$ exhibits type-II superconductivity, that evolves from weak-coupling BCS for $x=0.15$ to intermediate coupling for $x=0.25$ and 0.35. Electrical resistivity measurements up to a pressure of 2.5 GPa reveal that $T_{\mathrm{c}}(P)$ for $x=0.25$ and 0.35 has a shallow maximum with $T_{\mathrm{c}}^{\max }$ is 4.2 and 4.7 K at $P\sim 0.3$ and 0.7 GPa, respectively, whereas a monotonic decrease is observed for $x=0.15$. Using the McMillan equation, with the Debye temperature ${\Theta }_{\mathrm{R}}$ extracted from the resistance data under pressure as input, we find a smooth variation of $T_{\mathrm{c}}$ with the electron-phonon coupling strength ${\lambda }_{\mathrm{ep}}$ spanning the entire pressure and concentration range, from PdTe${}_2$ to 35 at.\% Au substitution. We conclude superconductivity across the Au${}_x$Pd${}_{1-x}$Te${}_2$ series under pressure is governed by a delicate balance between lattice stiffening and the strength of the electron phonon coupling.

12pages, 13figures in the main manuscript