Correlated states in β-Li2IrO3 driven by applied magnetic fields

Abstract

Magnetic honeycomb iridates are thought to show strongly spin-anisotropic exchange interactions which, when highly frustrated, lead to an exotic state of matter known as the Kitaev quantum spin liquid. However, in all known examples these materials magnetically order at finite temperatures, the scale of which may imply weak frustration. Here we show that the application of a relatively small magnetic field drives the three-dimensional magnet β-Li2IrO3 from its incommensurate ground state into a quantum correlated paramagnet. Interestingly, this paramagnetic state admixes a zig-zag spin mode analogous to the zig-zag order seen in other Mott-Kitaev compounds. The rapid onset of the field-induced correlated state implies the exchange interactions are delicately balanced, leading to strong frustration and a near degeneracy of different ground states.

Unconventional magnetic field response of the hyperhoneycomb Kitaev magnet β−Li2IrO3

“…Remarkably, all experimental data reported so far for Kitaev materials show that their response to the magnetic field depends very strongly on its direction. This is true for the layered compounds Na 2 IrO 3 [10], α-Li 2 IrO 3 [46], and α-RuCl 3 [29][30][31]47], as well as for the three-dimensional (3D) iridates β-Li 2 IrO 3 [21,24] and γ-Li 2 IrO 3 [19,48]. Here we revisit the case of the hyper-honeycomb β-Li 2 IrO 3 and show that its strongly anisotropic response signifies a large separation of energy scales between the relevant microscopic interactions, and can thus be used to extract information about the relative strength of these interactions in a direct way.…”

“…At zero field, the system orders magnetically below T N = 38 K, with the spins forming a noncoplanar, incommensurate (IC) modulation, with propagation wavevector Q = (0.57, 0, 0) in the orthorhombic frame, and two counter-rotating sets of moments [14], similar to those in γ-Li 2 IrO 3 [15] and α-Li 2 IrO 3 [18]. A magnetic field along b destroys the IC order at a characteristic field H * b ∼ 2.8 T, beyond which the spins show a uniform Q = 0 coplanar phase, comprising a ferromagnetic (FM) component along the field and a robust zigzag component along a [21]. These components are also present below H * b , but are too small to be detected at zero field [49,50].…”

Resonant x-ray scattering reveals possible disappearance of magnetic order under hydrostatic pressure in the Kitaev candidate γ−Li2IrO3

“…One experimental approach to achieving this goal is to apply an external perturbation and study the evolution of the magnetic ground state. For example, a magnetic field applied to β-Li 2 IrO 3 suppresses the spiral order and stabilizes a canted zig-zag spin texture, as observed by recent resonant x-ray scattering studies 16 . Hydrostatic pressure can also be a useful control parameter.…”

“…4B; the dark region indicates the observed extent of the spiral magnetic order, and the shaded region represents the simplest associated phase boundary. Ongoing studies of this material indicate paramagnetic behavior with rapidly emerging magnetic anisotropy favoring the b (easy) axis direction 12,25 at ambient pressure. As T approaches 0 K, P c likely continues to represent a sharp phase boundary between the spiral magnetic order and the as-yet undetermined highpressure electronic phase; the sharp disappearance could signal a first-order quantum phase transition.…”

“…Under an applied magnetic field, a correlated paramagnet which admixes the broken symmetry of zig-zag order 16,26 appears to be the next competitive magnetic ground state at ambient pressure. However the transition observed under applied magnetic field appears to be continuous, in contrast to the pressure-tuned transition at P c ; a different ground state may emerge in this case.…”