2016/07/31 by Yi Zhou, Kazushi Kanoda, Tai-Kai Ng · 5 citations
Physics and Astronomy · #cond-mat.str-el
paper · pdf · doi:10.1103/revmodphys.89.025003
published as Rev. Mod. Phys. 89, 025003 (2017) · Invited by RMP
arxiv created 2017/04/20 · arxiv updated 2017/04/21
This article is an introductory review of the physics of quantum spin liquid (QSL) states. Quantum magnetism is a rapidly evolving field, and recent developments reveal that the ground states and low-energy physics of frustrated spin systems may develop many exotic behaviors once we leave the regime of semi-classical approaches. The purpose of this article is to introduce these developments. The article begins by explaining how semi-classical approaches fail once quantum mechanics become important and then describes the alternative approaches for addressing the problem. We discuss mainly spin 1/2 systems, and we spend most of our time in this article on one particular set of plausible spin liquid states in which spins are represented by fermions. These states are spin-singlet states and may be viewed as an extension of Fermi liquid states to Mott insulators, and they are usually classified in the category of so-called SU(2), U(1) or Z2 spin liquid states. We review the basic theory regarding these states and the extensions of these states to include the effect of spin-orbit coupling and to higher spin (S>1/2) systems. Two other important approaches with strong influences on the understanding of spin liquid states are also introduced: (i) matrix product states and projected entangled pair states and (ii) the Kitaev honeycomb model. Experimental progress concerning spin liquid states in realistic materials, including anisotropic triangular lattice systems (κ-(ET)2Cu2(CN)3 and EtMe3Sb[(Pd(dmit)2]2), kagome lattice systems (ZnCu3(OH)6Cl2) and hyperkagome lattice systems (Na4Ir3O8), is reviewed and compared against the corresponding theories.