Investigation of magnetic order influenced phonon and electron dynamics in MnBiTe and Sb doped MnBiTe through terahertz time-domain spectroscopy
arXiv:2403.11580
Abstract
MnBiTe, the first topological insulator with inherent magnetic ordering, has attracted significant attention recently for providing a platform to realize several exotic quantum phenomena at relatively higher temperatures. In this work, we have carried out an exhaustive investigation of MnBiTe and Sb doped MnBiTe thin films using THz time-domain spectroscopy. The extracted real THz conductivity displays a strong IR active E phonon absorption peak (at 1.5 THz) merged on top of the Drude-like contributions from bulk and surface electrons. The extracted parameters from the THz conductivity data fitted to the Drude-Fano-Lorentz model, show significant changes in their temperature dependence around the magnetic ordering Néel temperature of 25K, which is suggestive of the coupling between magnetic ordering and electronic band structure. The frequency of the E phonon displays an anomalous blue-shift with increasing temperatures by 0.1 THz (7 %) for MnBiTe and 0.2 THz (13 %) for Sb doped MnBiTe between 7K and 250K. The line-shape of the E phonon mode in Sb doped MnBiTe shows significant Fano asymmetry compared to that of MnBiTe, indicating that Sb doping plays an important role in the Fano interference between the phonons and the electrons, in this system. These results indicate that the anomalous phonon behaviour seen in MBT arise mainly from positive cubic anharmonicity induced self energy parameter, whereas both anharmonicity and the electron phonon coupling are at play in making the relatively higher anomalous blue shift of phonons in MBST. Our studies provide the first comprehensive understanding of the phonon and electron dynamics of MnBiTe and Sb doped MnBiTe in the THz range using time-domain THz spectroscopy.