Characterization of the charge density wave transition and observation of the amplitude mode in LaAuSb2

Abstract

In order to elucidate the charge density wave (CDW) nature in ${\mathrm{LaAuSb}}_{2}$, we have carried out the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, as well as ultrafast pump-probe spectroscopy measurements on single crystalline ${\mathrm{LaAuSb}}_{2}$. The CDW phase transition has been characterized by marked features near ${T}_{C}\ensuremath{\simeq}88\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. In particular, the obtained Hall carrier concentration and electronic thermal conductivity exhibit significant reduction as ${T}_{C}$ drops, providing strong evidence for partial gapping of the Fermi surfaces during the CDW phase transition. Furthermore, the ultrafast pump-probe spectroscopy reveals pronounced oscillatory features in the photoinduced transient reflectivity in the CDW ordered state. A characteristic oscillation mode with frequency of about 0.32 THz was extracted. The comparison of the obtained oscillation frequency with the frequencies of the amplitude mode in the well-studied CDW analogue ${\mathrm{LaAgSb}}_{2}$ allows us to ascribe the observation to the amplitude mode of CDW collective excitations in ${\mathrm{LaAuSb}}_{2}$.