How heat propagates in liquid <sup>3</sup>He.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38413651.
- Also identified by DOI 10.1038/s41467-024-46079-0 and PMC identifier 10899593.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
In Landau's Fermi liquid picture, transport is governed by scattering between quasi-particles. The normal liquid <sup>3</sup>He conforms to this picture but only at very low temperature. Here, we show that the deviation from the standard behavior is concomitant with the fermion-fermion scattering time falling below the Planckian time, <math xmlns="http://www.w3.org/1998/Math/MathML"> <mfrac><mrow><mi>ℏ</mi></mrow> <mrow> <msub><mrow><mi>k</mi></mrow> <mrow><mi>B</mi></mrow> </msub> <mi>T</mi></mrow> </mfrac> </math> and the thermal diffusivity of this quantum liquid is bounded by a minimum set by fundamental physical constants and observed in classical liquids. This points to collective excitations (a sound mode) as carriers of heat. We propose that this mode has a wavevector of 2k<sub>F</sub> and a mean free path equal to the de Broglie thermal length. This would provide an additional conducting channel with a T <sup>1/2</sup> temperature dependence, matching what is observed by experiments. The experimental data from 0.007 K to 3 K can be accounted for, with a margin of 10%, if thermal conductivity is the sum of two contributions: one by quasi-particles (varying as the inverse of temperature) and another by sound (following the square root of temperature).