Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl3

Abstract

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general.

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

“…While indications for a field-induced spin liquid in Heisenberg-Kitaev models were found in numerical simulations in Ref. [19], a full theory is not available. Alternatively, the phase above H c could be adiabatically connected to the high-field limit, and the soft mode would then correspond to a high-field magnon.…”

“…Interestingly, NMR measurements with fields in the specific direction H c performed down to 4 K have indicated the formation of a sizable * Corresponding author: a.wolter@ifw-dresden.de spin gap at high fields [30]. Additionally, numerical exactdiagonalization studies of an extended Heisenberg-Kitaev model found hints for a transition from zigzag magnetic ordering to a spin-liquid state when applying a magnetic field [19].…”

“…The magnetic interactions between the Ru 3+ magnetic moments are believed to be described by a variant of the Heisenberg-Kitaev model [10]: Electronic-structure calculations indicate that the Kitaev interaction in α-RuCl 3 is ferromagnetic and indeed defines the largest exchange energy scale [19,20]. However, the debate about the spin model most appropriate for α-RuCl 3 -likely to include Heisenberg and off-diagonal exchange interactions, possibly also beyond nearest neighbors-has not been settled [19][20][21][22][23][24][25][26][27][28].…”

High-pressure magnetization and NMR studies of α−RuCl3

“…We first present data of a crystal measured under 12 T field applied along the c-axis, in which case the T N is less affected by field 22,23,36 . In the paramagnetic phase, nine NMR lines are expected, given one center line and two satellites for each 35 Cl site, and three inequivalent …”

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

“…15 For example, in α-RuCl 3 (RuCl 3 ), an actively studied KSL candidate, comprehensive ab initio computations and recent dynamical studies 16,17 suggest that ferromagnetic K and antiferromagnetic Γ interactions are dominant and comparable in magnitude, while J is negligible. [18][19][20] The balance of these and additional small further neighbor interactions causes RuCl 3 and other KSL candidates to magnetically order at low temperature; however, it is still unclear whether or not the often-large Γ interaction prefers magnetic ordering. Meanwhile, the community has attempted to revive the possibility of a KSL in RuCl 3 by applying a small magnetic field, with the effect of entering a potential spin liquid phase with no magnetization.…”