Charge-density-wave orderings in ${\mathrm{LaAgSb}}_2:$ An x-ray scattering study

X-ray scattering measurements on ${\mathrm{LaAgSb}}_2$ have revealed the onset of charge-density-wave (CDW) modulations associated with anomalies in the resistivity and magnetic susceptibility of this compound. Below the transition temperature of $T_{1,\mathrm{C}\mathrm{D}\mathrm{W}}=207\mathrm{}\mathrm{K},$ a periodic charge and lattice modulation with ${\tau }_1\sim 0.026(2\pi /a)$ develops along the a direction of the tetragonal structure $\mathrm{}(a<c).$ Further lowering of the temperature results in an additional charge-density-wave ordering below $T_{2,\mathrm{C}\mathrm{D}\mathrm{W}}=186\mathrm{}\mathrm{K}$ along the c direction with ${\tau }_2\sim 0.16(2\pi /c).\mathrm{}$ This ordering is associated with a rather weak anomaly in the c-axis resistivity that was previously unnoticed. With decreasing temperature, the wave vector of this second CDW locks into a commensurate value of $\frac{1}{6}(2\mathrm{}\pi /c)$ at $164(\pm 1)\mathrm{K}.$ The order parameters of ${\tau }_1-\mathrm{C}\mathrm{D}\mathrm{W}$ and ${\tau }_2-\mathrm{C}\mathrm{D}\mathrm{W}$ were deduced from the integrated intensities of the $\left(1\mathrm{}-{\tau }_{1}07\right)$ and $\left(1\mathrm{}07-{\tau }_2\right)$ satellite peaks, respectively, and are in good agreement with the BCS order parameter. The generalized susceptibility was also calculated, revealing enhanced nesting features for the observed modulation wave vectors.