Supersonic propagation of lattice energy by phasons in fresnoite

Abstract

Controlling the thermal energy of lattice vibrations separately from electrons is vital to many applications including electronic devices and thermoelectric energy conversion. To remove heat without shorting electrical connections, heat must be carried in the lattice of electrical insulators. Phonons are limited to the speed of sound, which, compared to the speed of electronic processes, puts a fundamental constraint on thermal management. Here we report a supersonic channel for the propagation of lattice energy in the technologically promising piezoelectric mineral fresnoite (Ba2TiSi2O8) using neutron scattering. Lattice energy propagates 2.8−4.3 times the speed of sound in the form of phasons, which are caused by an incommensurate modulation in the flexible framework structure of fresnoite. The phasons enhance the thermal conductivity by 20% at room temperature and carry lattice-energy signals at speeds beyond the limits of phonons.

Giant isotope effect on phonon dispersion and thermal conductivity in methylammonium lead iodide

“…The observed zone boundary softening of the LA phonons ( Fig. 1E) causes a substantial fraction of the LA phonon density of states to have a reduced group velocity (27), which would tend to lower the LA phonon contribution to thermal conductivity. However, such large changes in the phonon dispersion curves can also change the phase space for the allowed three-phonon scattering processes controlling thermal conductivity (28,29), making thermal transport difficult to predict from a simple inspection of the dispersion curves.…”

Partial ordering and phase elasticity in the MnGe short-period helimagnet

“…Historically, this picture was developed independently by Dzyaloshinskii [33] to describe the transition from helical to ferromagnetic order and by de Gennes [34] to model the alignment of cholesteric liquid crystals by a magnetic field. It also explains supersonic vibrations in a compound with flexible crystal structure [35]. Solitons are mobile domain walls between essentially commensurate domains, and their lattice describes the continually accumulating phase shifts near the transition to commensurate order.…”

Unveiling phonons in a molecular qubit with four-dimensional inelastic neutron scattering and density functional theory

“…Moreover, the recent advent of spectrometers combining the time-of-flight technique with position-sensitive detectors makes measuring the fourdimensional scattering function SðQ; ωÞ in large portions of the reciprocal space possible 8,21,35,36 . This experimental method is largely applied to study phonon dispersions in inorganic systems with extended structures [37][38][39][40][41] , but it has never been applied to complex molecular crystals. This work focuses on VOacetylacetonate ([VO(acac) 2 ]), a prototypical complex embedding the vanadyl (VO) unit, archetype of a new generation of molecular qubits with long coherence times up to high temperatures 14,16,30 .…”