Possible Intermediate Quantum Spin Liquid Phase in α-RuCl3 under High Magnetic Fields up to 100 T
Y. Matsuda and Kindo Group
Quantum spin liquid (QSL) constitutes a topological state of matter in frustrated magnets, where the constituent spins remain disordered even down to absolute zero temperature and share long-range quantum entanglement. Due to the lack of rigorous QSL ground states, such ultra quantum spin states are less well-understood in systems in more than one spatial dimension before Alexei Kitaev introduced the renowned honeycomb model with bond-dependent exchange.
The 4d spin-orbit magnet α-RuCl3 has been widely accepted as a prime candidate for Kitaev material. This compound is now believed to be described by the K-J-Γ-Γ’ effective model that includes the Heisenberg J(1, 3), Kitaev exchange K, and the symmetric off-diagonal exchange terms. The Kitaev interaction originates from chlorine-mediated exchange through edge-shared octahedra arranged on a honeycomb lattice. Similar to most of Kitaev candidate, additional non-Kitaev terms, unfortunately, stabilize a zigzag antiferromagnetic order below TN ≈ 7 K in the compound. Given that, a natural approach to realizing the Kitaev QSL is to suppress the zigzag order by applying magnetic fields to the compound.
Recently, the theoretical studies point out an interesting two-transition scenario with a field-induced intermediate QSL phase under the out-of-plane magnetic field [1], which is later confirmed by a large Kitaev-term spin Hamiltonian also based on the K-J-Γ-Γ’ model [2]. With the precise model parameters determined from fitting the experimental thermodynamics data, they theoretically reproduced the suppression of zigzag order under the 7-T in-plane field, and find a gapless QSL phase located between two out-of-plane transition fields that are about 35 T and of 100-T class, respectively. However, because theoretical studies predict very high critical fields—where H
In this work, we report the magnetization (M) process of α-RuCl3 by applying magnetic fields (H) in various directions within the honeycomb plane and along the c* axis (out-of-plane) up to 100 T, and find clear experimental evidence supporting the two-transition scenario. Here, the c* axis is the axis perpendicular to the honeycomb plane. Under fields applied along and close to the c* axis, an intermediate phase is found bounded by two transition fields H

Fig. 1. The field-angle phase diagram that summarizes the values of transition fields determined from both the experimenal (black solid markers) and the calculated (grey open ones) HC, H
References
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