Quantum Spin Liquids and Fractionalization

Nandini Trivedi

譲治 那須, Joji Nasu, 幸年 求 +3 more

Yukitoshi Motome

Yochai Werman, Shubhayu Chatterjee, Siddhardh C. Morampudi +1 more

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 interplane 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 Uð1Þ QSL with a Fermi surface-and consider both clean and disordered systems.In all cases, the in-plane and c-axis thermal conductivities have a different power-law dependence on temperature because of the different mechanisms of transport in the two directions: In the planes, the thermal current is carried by fractionalized excitations, whereas the interplane current is carried by integer (nonfractional) excitations.In layered Z 2 and Uð1Þ QSLs with a Fermi surface, and in the disordered Z 2 QSL with a Dirac dispersion, the c-axis thermal conductivity is parametrically smaller than the in-plane one but parametrically larger than the phonon contribution at low temperatures.

Yochai Werman, Shubhayu Chatterjee, Siddhardh C. Morampudi +1 more

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 interplane thermal conductivity in layered QSLs carries a unique signature of fractionalization. We examine several types of gapless QSL phases - a Z2 QSL with either a Dirac spectrum or a spinon Fermi surface, and a U(1) QSL with a Fermi surface - and consider both clean and disordered systems. In all cases, the in-plane and c-axis thermal conductivities have a different power-law dependence on temperature because of the different mechanisms of transport in the two directions: In the planes, the thermal current is carried by fractionalized excitations, whereas the interplane current is carried by integer (nonfractional) excitations. In layered Z2 and U(1) QSLs with a Fermi surface, and in the disordered Z2 QSL with a Dirac dispersion, the c-axis thermal conductivity is parametrically smaller than the in-plane one but parametrically larger than the phonon contribution at low temperatures.

Maissam Barkeshli, Erez Berg, Steven Allan Kivelson

Electrons have three quantized properties-charge, spin, and Fermi statistics-that are directly responsible for a vast array of phenomena. Here we show how these properties can be coherently and dynamically stripped from the electron as it enters a certain exotic state of matter known as a quantum spin liquid (QSL). In a QSL, electron spins collectively form a highly entangled quantum state that gives rise to the fractionalization of spin, charge, and statistics. We show that certain QSLs host distinct, topologically robust boundary types, some of which allow the electron to coherently enter the QSL as a fractionalized quasi-particle, leaving its spin, charge, or statistics behind. We use these ideas to propose a number of universal, conclusive experimental signatures that would establish fractionalization in QSLs.