Finite field regime for a quantum spin liquid in α−RuCl3

Abstract

An external magnetic field can induce a transition in α-RuCl3 from an ordered zigzag state to a disordered state that is possibly related to the Kitaev quantum spin liquid. Here we present new field dependent inelastic neutron scattering and magnetocaloric effect measurements implying the existence of an additional transition out of the quantum spin liquid phase at an upper field limit Bu. The neutron scattering shows three distinct regimes of magnetic response. In the low field ordered state the response shows magnon peaks; the intermediate field regime shows only continuum scattering, and above Bu the response shows sharp magnon peaks at the lower bound of a strong continuum. Measurable dispersion of magnon modes along the (0, 0, L) direction implies non-negligible inter-plane interactions. Combining the magnetocaloric effect measurements with other data a T − B phase diagram is constructed. The results constrain the range where one might expect to observe quantum spin liquid behavior in α-RuCl3. arXiv:1903.00056v3 [cond-mat.str-el]

Electrical Probes of the Non-Abelian Spin Liquid in Kitaev Materials

“…In α-RuCl 3 , applying an approximately 10 T in-plane magnetic field destroys the zero-field magnetic ordering [53]. Numerous experiments are consistent with the fascinating possibility that the system then enters the non-Abelian spin-liquid phase highlighted above [50,[54][55][56][57][58][59][60][61]. Most strikingly, Kasahara et al [60] report thermal-Hall-conductance measurements that agree well with the quantized value expected from the hallmark chiral Majorana edge mode.…”

“…A growing body of evidence supports the realization of a non-Abelian spin-liquid phase in the Kitaev material α-RuCl 3 [50,[54][55][56][57][58][59][60][61]64]. This remarkable development strongly motivates proposals for probing individual fractionalized excitations in honeycomb Kitaev materials, as required for eventual topological-quantum-computing applications.…”

Magnetic field induced competing phases in spin-orbital entangled Kitaev magnets

“…One can imagine that quantum fluctuations may melt these competing orders and promote a spin liquid state, but we will not know whether this is true until the magnetic orders are explicitly taken into account in the quantum model. If the large unit cell orders (partially) survive under quantum fluctuations, the magnon bands are typically flat and very close to each other such that they appear like the excitation continuum seen in inelastic neutron scattering experiments, which is often interpreted as fractionalized excitations in a quantum spin liquid [16][17][18]44,45]. The resulting two magnon excitations will also form a very broad continuum at low energies.…”

“…At zero magnetic field, this material orders magnetically in the zigzag (ZZ) order [14,15]. Upon the application of an external field, neutron scattering experiments [16][17][18] find an intermediate window of fields before the system enters the polarized state, where sharp magnon modes are absent but a scattering continuum appears instead. Under a [111] field (perpendicular to the honeycomb plane), the measured thermal Hall conductivity above the ordering temperature T N ≈ 7 K follows the predicted trend of itinerant Majorana fermions in the pure Kitaev model [19].…”

Emergence of nematic paramagnet via quantum order-by-disorder and pseudo-Goldstone modes in Kitaev magnets

“…The experiment mentioned above [23] and recent inelastic neutron scattering experiments [15,20,[24][25][26] have motivated a number of numerical studies [27][28][29][30][31] in an effort to identify possible nontrivial phases in theoretical spin models proposed for realistic materials. For instance, the K model, which is considered as a minimal model describing a broad class of Kitaev materials including α-RuCl 3 , has been studied with an external magnetic field.…”