Pressure effect on the charge-density-wave order in pure and doped (La,R)AgSb$_2$ (R = Ce, Nd) compounds*

We studied the pressure dependent resistivity, $\rho(T)$, of single-crystals of pure and doped (La,R)AgSb$_2$ (R = Ce, Nd) compounds, up to 23 kbar, for temperatures $2 \leq T \leq 300$ K. LaAgSb$_2$ displays features at $T_1 = 210$ K, and $T_2 = 185$ K, due to the formation of charge-density-wave (CDW) order along the $a-$ and $c-$ axis of the tetragonal structure, respectively. The effect of pressure in LaAgSb$_2$ is to lower $T_1$ at the rate of -4.5 K/kbar. Partial substitutions of Nd and Ce for La depress $T_1$ as well, and the effect of pressure is to lower it further. The value of $T_1 = 112$ K for La$_{0.75}$Nd$_{0.25}$AgSb$_2$ drops with pressure at the rate of -5.8 K/kbar, until the feature in $\rho(T)$ cannot be identified above 12 kbar, suggesting the closure of the CDW gap. The effect of pressure on La$_{0.9} $Ce$_{0.1}$AgSb$_2$, and La$_{0.8}$Ce$_{0.2}$AgSb$_2$ is to depress $T_1$ at the rate of $\approx -10$ K/kbar, with the suppression of CDW order for $P \approx 12$ and $\approx 8$ kbar, respectively. The $\rho(T)$ data for the Ce-doped compounds show upturns at low temperatures due to the Kondo effect, and the minimum in $\rho(T)$ is lowered with pressure.