Interplay between charge density wave order and superconductivity in $\mathrm{La}\mathrm{Au}{\mathrm{Sb}}_2$ under pressure

We report superconductivity below $T_{\mathrm{c}}=0.64$ K in the charge density wave (CDW) ordered material ${\mathrm{LaAuSb}}_2$, from measurements of the electrical resistivity, specific heat, and ac magnetic susceptibility. To investigate the interplay between superconductivity and CDW order in ${\mathrm{LaAuSb}}_2$, we measured the resistivity under pressures up to 2.0 GPa and constructed the temperature-pressure phase diagram. With the application of pressure, $T_{\mathrm{c}}$ increases gradually before exhibiting a sudden jump at around 0.64 GPa, while the CDW order is suppressed to lower temperatures before abruptly vanishing at the same pressure. We suggest that the jump of $T_{\mathrm{c}}$ may be due to the enhancement of the density of states with the closure of the CDW energy gap when CDW order is suppressed. On the other hand, the normalized upper critical field $H_{\mathrm{c}2}$ changes little with pressure, suggesting that orbital limiting is the dominant pair-breaking mechanism in ${\mathrm{LaAuSb}}_2$.

Figure 1

(a) Resistivity of ${\mathrm{LaAuSb}}_2$ at ambient pressure as a function of temperature $\rho (T$) from 250 K down to 0.3 K. (inset) $d\rho /dT$, which was used to define $T_{\mathrm{CDW}}$. Temperature dependence of the (b) resistivity and (c) heat capacity $C_{\mathrm{p}}$, both measured upon warming (red lines) and cooling (navy lines) which show the presence of a CDW transition at around 78 K, as marked by the vertical dashed line.

Figure 2

(a) Low temperature $\rho (T$) of ${\mathrm{LaAuSb}}_2$, which shows the presence of a superconducting transition. The arrow marks the position of $T_{\mathrm{c}}$, corresponding to the midpoint of the resistivity drop. (b) Electronic contribution to the heat capacity as $C_{\mathrm{e}}/T$ and the ac susceptibility ${\chi }_{\mathrm{ac}}(T$) at low temperature, where the inset shows $C_{\mathrm{p}}(T$)/$T$ versus $T^2$ and the corresponding fitting with $C_{\mathrm{p}}/T={\gamma }_{\mathrm{n}}+\beta T^2$.

Figure 3

Temperature dependence of the resistivity of ${\mathrm{LaAuSb}}_2$ under various pressures, measured upon cooling. The inset shows the derivative $d\rho /dT$, where the arrows mark the CDW transition temperatures.

Figure 4

(a) Low-temperature resistivity of ${\mathrm{LaAuSb}}_2$ under various pressures, showing the evolution of the superconducting transition with pressure. (b) The upper critical field ($H_{\mathrm{c}2}$) of ${\mathrm{LaAuSb}}_2$ as a function of $T/T_{\mathrm{c}}$ at various pressures, normalized by the product of $T_{\mathrm{c}}$ and the slope of $H_{\mathrm{c}2}$ near $T_{\mathrm{c}}$. The calculated curve from the WHH model (dashed line) is also displayed.

Figure 5

(a) Temperature-pressure phase diagram of ${\mathrm{LaAuSb}}_2$. $T_{\mathrm{CDW}}$ is determined from the derivative of the resistivity, where the error bars in $T_{\mathrm{CDW}}$ correspond to the full width at half minimum of the feature at the transition in $d\rho /dT$. $T_{\mathrm{c}}$ from $\rho \left(T\right)$ corresponds to the temperature where there is a drop to 50% of the normal-state value. The error bars in the $T_{\mathrm{c}}$ of the resistivity represents where there is a 10% and 90% drop of the resistivity. The error bars for the pressure are all less than 0.015 GPa, and are, therefore, smaller than the symbol size. (b) Pressure dependence of the residual resistivity ${\rho }_0$.