Abstract
The thermal conductivity of the quasi-2D organic spin-liquid candidate (dmit-131) was measured at low temperatures, down to 0.07 K. We observe a vanishingly small residual linear term , in vs as . This shows that the low-energy excitations responsible for the sizable residual linear term in the specific heat , seen in vs as , are localized. We conclude that there are no mobile gapless excitations in this spin-liquid candidate, in contrast with a prior study of dmit-131 that reported a large value [ , Science 328, 1246 (2010)]. Our study shows that dmit-131 is in fact similar to , another quasi-2D organic spin-liquid candidate where a vanishingly small and a sizable are seen. We attribute heat conduction in these organic insulators without magnetic order to phonons undergoing strong spin-phonon scattering, as observed in several other spin-liquid materials.
- Received 25 April 2019
- Revised 4 September 2019
DOI:https://doi.org/10.1103/PhysRevX.9.041051
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Quantum spin liquids (QSLs) are a new, exotic class of materials in which neighboring electron spins interact in such a way that prevents them from settling into any fixed arrangement. As a result, these insulators lack net magnetism, and the spins fluctuate right down to the lowest temperatures. Theory predicts that, in QSLs, quasiparticles known as spinons—where the spin of an electron moves as an independent entity—might transport heat in much the same way as electrons do in common metals, however, experiments have yet to confirm this. Using thermal conductivity measurements, we investigate this issue in a promising QSL candidate and find no evidence that spinons contribute to heat transport.
Thermal conductivity measurements are ideal for this sort of work: The change in conductivity as temperature drops is sensitive only to mobile particles and quasiparticles. In particular, spin excitations such as spinons should contribute to the conductivity a linear dependence on temperature. We measure the thermal conductivity down to 0.07 K on eight high-quality crystals of a spin-liquid candidate. Contrary to previous reports, we find no evidence of a linear contribution, suggesting that spin excitations in this material are not mobile.
We attribute heat conduction in this material to phonons (quantized vibrations of the atomic lattice) scattering off of spin excitations. Comparison with published data on numerous QSL candidates shows, in fact, that this is a widespread phenomenon that should be considered in any future theory of QSLs.
