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arXiv · 2107.11332

Leggett Modes Accompanying Crystallographic Phase Transitions

Quintin N. Meier·Daniel Hickox-Young·Geneva Laurita·Nicola A. Spaldin·James M. Rondinelli·Michael R. Norman
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Abstract

Higgs and Goldstone modes, well known in high energy physics, have been realized in a number of condensed matter physics contexts, including superconductivity and magnetism. The Goldstone-Higgs concept is also applicable to and gives rise to new insights on structural phase transitions. Here, we show that the Leggett mode, a collective mode observed in multi-band superconductors, also has an analog in crystallographic phase transitions. Such structural Leggett modes can occur in the phase channel as in the original work of Leggett, \href{https://doi.org/10.1143/PTP.36.901}{Prog.\ Theor.\ Phys.\ \textbf{36}, 901 (1966)}. That is, they are antiphase Goldstone modes (anti-phasons). In addition, a new collective mode can also occur in the amplitude channel, an out-of phase (antiphase) Higgs mode, that should be observable in multi-band superconductors as well. We illustrate the existence and properties of these structural Leggett modes using the example of the pyrochlore relaxor ferroelectric, Cd$_2$Nb$_2$O$_7$.

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Quintin N. Meier, Daniel Hickox-Young, Geneva Laurita, Nicola A. Spaldin, James M. Rondinelli, Michael R. Norman. 2021-07-23. Leggett Modes Accompanying Crystallographic Phase Transitions. https://doi.org/10.1103/physrevx.12.011024

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