PbTe crystals have a soft transverse optical phonon mode in the terahertz frequency range, which is known to efficiently decay into heat-carrying acoustic phonons, resulting in anomalously low thermal conductivity. Here, we studied this phonon via polarization-dependent terahertz spectroscopy. We observed softening of this mode with decreasing temperature, indicative of incipient ferroelectricity, which we explain through a model including strong anharmonicity with a quartic displacement term. In magnetic fields up to 25T, the phonon mode splits into two modes with opposite handedness, exhibiting circular dichroism. Their frequencies display Zeeman splitting together with an overall diamagnetic shift with increasing magnetic field. Using a group-theoretical approach, we demonstrate that these observations are the result of magnetic field-induced morphic changes in the crystal symmetries through the Lorentz force exerted on the lattice ions. Our study thus reveals a novel process of controlling phonon properties in a soft ionic lattice by a strong magnetic field.
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Publication: https://arxiv.org/abs/2107.07616
Presenters
Andrey Baydin
Rice University
Authors
Andrey Baydin
Rice University
Felix Hernandez
Universidade de S ̃ao Paulo
Martin A Rodriguez-vega
University of Texas at Austin, Los Alamos National Laboratory
Anderson Okazaki
Instituto Nacional de Pesquisas Espaciais
Fuyang Tay
Rice Univ
Gary T Noe
Rice Univ
Ikufumi Katayama
Yokohama National University, Yokohama, Japan, Yokohama National University
Jun Takeda
Yokohama National University, Yokohama, Japan, Yokohama National University
Hiroyuki Nojiri
Tohoku University, Sendai, Japan, Tohoku University
