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

Abstract

Transition metal ditellurides with the CdI2-type structure are materials with intriguing superconducting and electronic properties as demonstrated by PdTe2. Gold substituted PdTe2, AuxPd1-xTe2, adopts the CdI2-type structure for a Pd content larger than 43 at.% at room temperature, and in this range enhanced superconductivity with a critical temperature (Tc) above 4 K has been reported (Kudo et al., PRB 93, 140505, 2016). Here we present the effect of pressure on the structural and superconducting properties of AuxPd1-xTe2 for x=0.15, 0.25 and 0.35 with Tc =2.7, 4.1, and 4.6 K at 1 atm, respectively. Synchrotron radiation x-ray diffraction shows that the CdI2-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 PdTe2 exhibits type-II superconductivity, that evolves from weak-coupling BCS for x = 0.15 to strong-coupling for x = 0.25 and 0.35. Electrical resistivity measurements up to a pressure of 2.5 GPa show that Tc(P) for x = 0.25 and 0.35 passes through a shallow maximum of 4.2 and 4.7 K at P ~ 0.3 and 0.7 GPa, respectively, compared to the monotonic decrease for x = 0.15. Furthermore, the pressure variation of the superconducting H - T phase diagram at each composition indicates that the superconducting properties remain essentially unchanged with pressure. The composition dependence of $T_{\rm c}$ is discussed by comparing the experimental results of AuxPd1-xTe2 to those of undoped PdTe2.

Figures (21)

• Figure 1: Diffraction patterns of Au$_{0.35}$Pd$_{0.65}$Te$_2$ measured at 0.25 and 7.91 GPa at room temperature, and the Rietveld refinement result of the lower pattern. Blue symbols (+), and red and green lines, represent the experimental diffraction intensity, the calculated intensity, and the residual error, respectively. The three sets of vertical bars below the diffraction patterns indicate the diffraction angles of the $P\overline{3}m$1, $Fm\overline{3}m$, and $P4_12_12$ structure for Au$_x$Pd$_{1-x}$Te$_2$, gold ($\ast$ in the pattern), and TeO$_2$ ($\blacktriangledown$), respectively. The cross symbol ($\times$) marks an unassigned peak. The goodness of fit for this pattern is 4.20.
• Figure 2: Pressure variation of the lattice constants and volume normalized to the values at ambient pressure for Au$_x$Pd$_{{\rm 1}-x}$Te$_2$: (a) $a/a_0$ and $c/c_0$ and (b) $V/V_0$. The inset of (a) shows the ratio $c/a$ of the lattice constants as a function of pressure. Closed green, red, and blue circles show values for $x=0.15$, 0.25 and 0.35, respectively. A broken line in (b) is the result of a fit to the BM-EOS for $x=0.35$ (see text). Open circles show those of PdTe$_2$, obtained from our previous work Furue2021, for comparison.
• Figure 3: Ambient pressure experimental results of the superconducting transition in Au$_{0.35}$Pd$_{0.65}$Te$_2$: (a) electrical resistance as a function of temperature, (b) zero field-cooled (ZFC) and field-cooled (FC) dc susceptibility $\chi$ measured at a field of $\mu_0H=1$ mT, (c) DC magnetization per unit volume as a function of applied field at temperatures of 2 and 3 K, and (d) temperature dependence of the electronic specific heat at magnetic fields from 0 to 1.5 T. The black dashed line shows the normal state $c_{\rm el}= \gamma T$. The red line shows $c_{\rm el}(T)$ of the superconducting state at zero field calculated with $\alpha=2$Johnson2013 (see text). Insets in (a) and (b) show a magnified view around the onset temperature of the superconducting transition. In (c) the lower, $H_{\rm c1}$, and upper critical field, $H_{\rm c2}$, are indicated by vertical arrows.
• Figure 4: Ambient pressure superconducting phase diagram, $B_{\rm c2}(T)$, of Au$_x$Pd$_{{\rm 1}-x}$Te$_2$ for $x=0.15$, 0.25 and 0.35. Closed and open circles are taken from the HC and DCM measurements, respectively. Solid lines are WHH model curves.
• Figure 5: Pressure variation of the superconducting transition of Au$_{0.35}$Pd$_{0.65}$Te$_2$ in the electrical resistivity. The inset shows $\rho(T)$ up to room temperature at increasing pressure. Color variations related to the experimental pressure are the same in the main frame and the inset.