Strongly coupled phonon fluid and Goldstone modes in an anharmonic quantum solid: Transport and chaos
Year: 2021
Type: article
Abstract: We study properties of thermal transport and quantum many-body chaos in a lattice model with $N\ensuremath{\rightarrow}\ensuremath{\infty}$ oscillators per site, coupled by strong anharmonic terms. We first consider a model with only optical phonons. We find that the thermal diffusivity ${D}_{\mathrm{th}}$ and chaos diffusivity ${D}_{L}$ (defined as ${D}_{L}={v}_{B}^{2}/{\ensuremath{\lambda}}_{L}$, where ${v}_{B}$ and ${\ensuremath{\lambda}}_{L}$ are the butterfly velocity and the scrambling rate, respectively) satisfy ${D}_{\mathrm{th}}\ensuremath{\approx}\ensuremath{\gamma}{D}_{L}$ with $\ensuremath{\gamma}\ensuremath{\gtrsim}1$. At intermediate temperatures, the model exhibits a quantum ``phonon fluid'' regime, where both diffusivities satisfy ${D}^{\ensuremath{-}1}\ensuremath{\propto}T$, and the thermal relaxation time and inverse scrambling rate are of the order the of Planckian timescale $\ensuremath{\hbar}/{k}_{B}T$. We then introduce acoustic phonons to the model and study their effect on transport and chaos. The long-wavelength acoustic modes remain long-lived even when the system is strongly coupled, due to Goldstone's theorem. As a result, for $d=1,2$, we find that ${D}_{\mathrm{th}}/{D}_{L}\ensuremath{\rightarrow}\ensuremath{\infty}$, while for $d=3, {D}_{\mathrm{th}}$ and ${D}_{L}$ remain comparable.
Authors: Evyatar Tulipman, Erez Berg
Institution: Weizmann Institute of Science
Language: English
Topic: Quantum many-body systems
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G6542276475
OpenAlex ID: W3212111191