Revealing Extremely Low Energy Amplitude Modes in the Charge-Density-Wave Compound LaAgSb_{2}.
Using infrared spectroscopy and ultrafast pump probe measurement, we have studied the two charge-density-wave (CDW) instabilities in the layered compound LaAgSb_{2}. The development of CDW energy gaps was clearly observed by optical spectroscopy, which removed most of the free carrier spectral weight. More interestingly, our time-resolved measurements revealed two coherent oscillations that softened by approaching the two phase transition temperatures, respectively. We addressed that these two oscillations come from the amplitude modes of CDW collective excitations, the surprisingly low energies (0.12 THz and 0.34 THz for the higher and lower temperature ones, respectively) of which are associated with the extremely small nesting wave vectors. Additionally, the amplitude and relaxation time of photoinduced reflectivity of LaAgSb_{2} single crystals stayed unchanged across the CDW phase transitions, which is quite rare and deserves further investigation.
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.|Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing 100875, China.
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Chen
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
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Zhang
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
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Zhang
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
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Dong
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.|Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
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Wang