Hot carrier dynamics and phonon anharmonicity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">ZrTe</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math> revealed with femtosecond transient optical spectroscopy
Ning Li, Weizheng Liang, Sheng‐Nian Luo
Abstract
We present a time-resolved ultrafast optical spectroscopy study on thermoelectric material ${\mathrm{ZrTe}}_{5}$, regarding its carrier decay dynamics and anharmonic decay of coherent optical phonons at 5--280 K. A reflectivity time series consists of a single exponential decay due to the relaxation of carriers via electron-phonon coupling and decaying oscillations due to coherent phonon vibration of the ${A}_{g}$ mode. The carrier decay characteristics follow the temperature-induced electronic transitions of ${\mathrm{ZrTe}}_{5}$. The coherent optical phonon vibrations can be well described with the anharmonicity model including lattice thermal expansion and phonon-phonon coupling. The phonon vibration frequency and dephasing time are obtained as a function of temperature, and decrease with increasing temperature. The effects of pump fluence are also explored.