4.8 Article

Magnetic Control of Soft Chiral Phonons in PbTe

Journal

PHYSICAL REVIEW LETTERS
Volume 128, Issue 7, Pages -

Publisher

AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.128.075901

Keywords

-

Funding

  1. National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC [DMR-1720595]
  2. SAo Paulo Research Foundation (FAPESP) [2015/16191-5, 2018/06142-5, 307737/2020-9]
  3. National Council for Scientific and Technological Development (CNPq)
  4. LANL LDRD Program
  5. U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Condensed Matter Theory Program
  6. NSF [DMR-2114825]
  7. Japan Society for the Promotion of Science (JSPS) [20H05662]
  8. Grants-in-Aid for Scientific Research [20H05662] Funding Source: KAKEN

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PbTe crystals possess a soft transverse optical phonon mode in the terahertz range, which softens with decreasing temperature and indicates incipient ferroelectricity. In the presence of a magnetic field, the phonon mode splits into two modes with opposite handedness, exhibiting circular dichroism. These observations are the result of magnetic field-induced morphic changes in crystal symmetries.
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 25 T, 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. Thus, our Letter reveals a novel process of controlling phonon properties in a soft ionic lattice by a strong magnetic field.

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