Abstract
Quantum spin liquids (QSLs) are intriguing phases of matter possessing fractionalized excitations. Several quasi-two dimensional materials have been proposed as candidate QSLs, but direct evidence for fractionalization in these systems is still lacking. In this paper, we show that the inter-plane thermal conductivity in layered QSLs carries a unique signature of fractionalization. We examine several types of gapless QSL phases - a $Z_2$ QSL with either a Dirac spectrum or a spinon Fermi surface, and a $U(1)$ QSL with a Fermi surface. In all cases, the in-plane and $c-$axis thermal conductivities have a different power law dependence on temperature, due to the different mechanisms of transport in the two directions: in the planes, the thermal current is carried by fractionalized excitations, whereas the inter-plane current is carried by integer (non-fractional) excitations. In layered $Z_2$ and $U(1)$ QSLs with a Fermi surface, the $c-$axis thermal conductivity is parametrically smaller than the in-plane one, but parametrically larger than the phonon contribution at low temperatures.
Highlights
Quantum spin liquids (QSLs) are phases of matter with intrinsic topological order, which cannot be characterized by local order parameters as typically used in symmetrybreaking phases
As a concrete example of the gapless Z2 QSL, one may consider the gapless phase of the Kitaev honeycomb model [16], which consists of spin-1=2 s interacting in an anisotropic manner on a two-dimensional hexagon lattice
We have studied the thermal conductivity in layered, gapless QSLs
Summary
Quantum spin liquids (QSLs) are phases of matter with intrinsic topological order, which cannot be characterized by local order parameters as typically used in symmetrybreaking phases Instead, their primary characteristic is the emergence of excitations with fractional quantum numbers [1,2,3,4,5,6]. Excitations pertinent to the type of QSL in question; in contrast, the thermal current between the planes must be carried by a gauge-invariant excitation with integer quantum numbers This is because the emergent gauge charge carried by fractionalized excitations is conserved separately in each layer, and a single spinon cannot move from one layer to the next. In some cases, the exponent of the interplane thermal conductivity is smaller than 3, and it is parametrically larger than the phonon contribution (proportional to T3) at sufficiently low temperatures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
