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.
Highlights
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
The anomaly at TI=38K (μ0H = 0 T) corresponds to the onset of a known incommensurate magnetic structure with order parameter ΨI and propagation vector q = (0.574, 0, 0)[18]. This highly triangular feature is indicative of a mean-field, second order transition which is strongly suppressed by an applied magnetic field, and completely disappears above H* (Fig. 1c)
The symmetries of the state consistent with the primary features of the data above H* are two-fold: G-type broken symmetry, explaining the appearance of the (2m, 0, 12 n± 2 + 6m) peaks and, F-type order, explaining the linear dependence of the the allowed structural peaks (2m, 0, 4n + 2m). These symmetries are broken by the applied magnetic field itself
Summary
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. The Mott–Kitaev iridates crystallize in 2D and 3D structures (the harmonic honeycombs6), and all known compounds are found to magnetically order at low temperature in one of two wα-aRyus:Cal3c7o–9m),manendsaunraitnec“ozmigm-zeangs”uprahtaeseor(dfoerun(fdouinndα-inNaα2,IβrOa3ndanγdLi2IrO36, 10, 11) This suggests that there are non-Kitaev terms in the Hamiltonian, relieving the frustration and obscuring any lowenergy signature of the Kitaev physics[5, 12, 13]. We find that in this configuration, a relatively small field can induce a strongly correlated state with zig-zag broken symmetry at the expense of the incommensurate order, providing evidence for strong correlations and a possible familial connection between the low-energy Hamiltonian of different Mott–Kitaev systems
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