α−RuCl3: A spin-orbit assisted Mott insulator on a honeycomb lattice

Abstract

We examine the role of spin-orbit coupling in the electronic structure of α-RuCl3, in which Ru ions in 4d 5 configuration form a honeycomb lattice. The measured optical spectra exhibit an optical gap of 220 meV and transitions within the t2g orbitals. The spectra can be described very well with firstprinciples electronic structure calculations obtained by taking into account both spin-orbit coupling and electron correlations. Furthermore, our x-ray absorption spectroscopy measurements at the Ru L edges exhibit distinct spectral features associated with the presence of substantial spin-orbit coupling, as well as an anomalously large branching ratio. We propose that α-RuCl3 is a spin-orbit assisted Mott insulator, and that the bond-dependent Kitaev interaction may be relevant for this compound.

Path to stable quantum spin liquids in spin-orbit coupled correlated materials

“…[2][3][4][5][6] Significant progress, however, has recently been made due to the availabilty of a new class of correlated materials, where strong spin-orbit coupling leads to various bond-dependent spin interactions, [7][8][9] thus resulting in magnetic frustation. These materials are Mott insulators with 4d and 5d transition metal elements, which include iridates and ruthenates [10][11][12][13][14] and come in two-dimensional (2D) or three-dimensional (3D) honeycomb variants. They have been particularly exciting because they intrinsically have a strong Kitaev interaction and therefore could potentially realize the Kitaev spin liquid (KSL) phase-an example of a Z 2 quantum spin liquid where the electron's spin À 1 2 fractionalizes into two degrees of freedom: itinerant Majorana fermions and Z 2 fluxes.…”

Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions

“…This includes the socalled Jackeli-Khaliullin-Kitaev (JKK) materials, a family of systems in which these magnetic ions occupy sites with three-fold coordination in a structure with edgesharing octahedra. [2][3][4] Significant experimental effort has been devoted to study JKK materials on the two-dimensional honeycomb lattice sturture [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and on the three-dimensional trivalent lattice structures in the harmonic honeycomb family. [12][13][14][15] The motivation behind this flurry of experimental activity is the possibility of realizing the Kitaev quantum spin liquid 2,3 because these lattice geometries promote the dominance of the Kitaev interactions between magnetic moments.…”

Field-induced quantum criticality in the Kitaev system α−RuCl3

“…We relate the data to theoretical calculations based on a J 1 -K 1 -1 -J 3 honeycomb model. Mott insulator with a layered structure of edge-sharing RuCl 6 octahedra arranged in a honeycomb lattice [1][2][3][4][5][6][7][8]. It has been suggested [9,10] that strongly spin-orbit-coupled Mott insulators with that lattice geometry realize bond-dependent magnetic "compass" interactions [11], which, if dominant, would lead to a quantum spin-liquid (QSL) ground state as discussed by Kitaev [12].…”