Coexistence of random singlets and disordered Kitaev spin liquid in H3LiIr2O6

Abstract

We combine static magnetic susceptibility χ (T ), muon-spin relaxation, and 1 H nuclear magnetic resonance measurements to explore the spin dynamics in the disordered-induced quantum spin liquid candidate H 3 LiIr 2 O 6 . Inverse Laplace transform analysis of the 1 H spin-lattice relaxation rate 1/T 1 enables us to identify two characteristic temperatures T g = 110 K and T * = 26 K. Below T g , a slower 1/T slow 1 component dictated by gapped excitations with a spin gap h = 30-38 K evolves distinctly from a faster 1/T fast 1 component pertaining to gapless excitations. Furthermore, we observe a sub-Curie divergent χ (T ) ∝ T −0.68 , a power-law dependent 1/T fast 1 ∝ T 1.4 , and a weakly activated 1/T slow 1 ∝ exp(− l /k B T ) ( l = 3-6 K) below T * = 26 K. All these features suggest the coexistence of a disordered spin-liquid state and spin singlets with spatially distributed gaps.

Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6

“…However, we find that a large distribution of δ values, as encoded by the standard deviation σ δ = 20 meV, is needed to account for the broader crystal field excitations in H 3 LiIr 2 O 6 and the relative intensity ratio between peaks A − B and C − D . This is consistent with the existence of slow H-ion motion at low temperature, which can generate variations of the local IrO 6 environment 20 , 24 . Thus, our Ir crystal field RIXS data, O XAS measurements and analysis is consistent with the existence of local bond-disorder on IrO 6 octahedra and points to an enhanced Ir–O hybridization as the leading mechanism favoring a dominant Kitaev-like exchange in H 3 LiIr 2 O 6 .…”

“…As a result, superexchange pathways are modified with respect to those of α -Li 2 IrO 3 and a different magnetic state is expected in H 3 LiIr 2 O 6 17 , 18 . Temperature-dependent measurements of the magnetic susceptibility in H 3 LiIr 2 O 6 show no evidence for long-range magnetic order down to 5 mK, despite a Curie–Weiss temperature θ C W ≈ −105 K, as confirmed by the NMR Knight shift 19 , 20 . The NMR relaxation rate rules out a spin glass in favor of dynamically fluctuating spins 19 .…”

“…Achieving a microscopic description of the magnetic state in H 3 LiIr 2 O 6 is complicated by disorder. Quasi-static H zero point motion 20 , 24 , 25 , present even in crystallographic pristine samples, can lead to local variations of the intra-layer exchange interactions 26 , 27 . Furthermore, the heavily faulted stacking structure due to the linear inter-layer O–H–O coordination might also result on random intra-layer magnetic exchanges 17 , 18 .…”

Beyond Kitaev physics in strong spin-orbit coupled magnets

“…The layered materials include, most notably, the d 5 compounds Na 2 IrO 3 [21][22][23][24][25][26], α-Li 2 IrO 3 [27,65,66], α-RuCl 3 [28-31, 67, 68], H 3 Li 2 IrO 6 [69][70][71], Ag 3 Li 2 IrO 6 [72][73][74] and Cu 2 IrO 3 [75][76][77], which typically have monoclinic (C 2/m or C 2/c ) or trigonal (R-3m * or R-3) symmetry [9] (see figure 2 for the typical edge-sharing geometry of ligands in these materials). More recent proposals include the family of d 5 -based ilmenites AIrO 3 with A = Mg, Zn, Cd [78,79], as well as a family of d 7 -based transition metal compounds [80][81][82][83], such as the delafossites Na 3 Co 2 SbO 6 and Na 2 Co 2 TeO 6 [84][85][86][87][88][89][90][91], Li 3 Co 2 SbO 6 [92], and also BaCo 2 (AsO 4 ) 2 and BaCO 2 (PO 4 ) 2 [93][94][95].…”

“…Finally, the points K = Γ are hidden SU(2) points with J = −K, as in the 2D model. The associated transformation T 6 has again the form of equation ( 21) when using the labeling of the six-site decomposition of (71).…”