Unusual spin dynamics in the low-temperature magnetically ordered state of Ag3LiIr2O6

Abstract

Recently, there have been contrary claims of Kitaev spin-liquid behavior and ordered behavior in the honeycomb compound Ag 3 LiIr 2 O 6 based on various experimental signatures. Our investigations on this system reveal a low-temperature ordered state with persistent dynamics down to the lowest temperatures. Magnetic order is confirmed by clear oscillations in the muon spin relaxation (μSR) time spectrum below 9 K until 52 mK. Coincidentally in 7 Li nuclear magnetic resonance, a wipeout of the signal is observed below ∼10 K, which again strongly indicates magnetic order in the low-temperature regime. This is supported by our density functional theory calculations which show an appreciable Heisenberg exchange term in the spin Hamiltonian that favors magnetic ordering. The 7 Li shift and spin-lattice relaxation rate also show anomalies at ∼50 K. They are likely related to the onset of dynamic magnetic correlations, but their origin is not completely clear. Detailed analysis of our μSR data is consistent with a coexistence of incommensurate Néel and striped environments. A significant and undiminished dynamical relaxation rate (∼5 MHz) as seen in μSR deep into the ordered phase indicates enhanced quantum fluctuations in the ordered state.

Raman fingerprints of fractionalized Majorana excitations in the honeycomb iridate Ag3LiIr2O6

“…This is owing to the intricate role of disorder present in these derived candidates which has been theoretically predicted to enhance the low-energy density of states of the Majorana fermionic excitations [28,29]. Equating the upper cutoff of ∼300 cm −1 of this broad Raman response to 3|J K | (J K is the Kitaev interaction strength), the theoretical estimate for the band edge of the Raman continuum from Majorana fermions [6], yields |J K | ≈ 12 meV which is in reasonable agreement with the Kitaev interaction strength obtained for this compound from recent density functional theory (DFT) calculations (J K ≈ 11.4 meV) [25].…”

“…In field-cooled (FC) mode, the sample was cooled under the applied magnetic field and the magnetization was measured on warming. Figure 1 ZFC and FC curves as reported earlier [25] to be originated from the quenched disorder of naturally occurring stacking faults present in the sample inducing localized moments. The inset of Fig.…”

“…The initial magnetic and thermodynamic studies on disordered Ag 3 LiIr 2 O 6 samples with extended Ag positional defects within the honeycomb layers, entrenched the validity of Kitaev QSL physics in this system by affirming the absence of any long-range magnetic order along with a two-step release of spin entropy at crossover temperatures T h ∼ 75 K and T l ∼ 13 K [23]. Later, a cleaner batch of samples exhibited a more pronounced and clear transition to long-range ordering below the Néel temperature T N ∼ 10 K while spin fluctuations remain present even in the ordered state down to 4.2 K [21,24,25]. Moreover, recent x-ray absorption and resonant inelastic x-ray scattering measurements on high-quality crystals confirmed the existence of a spin liquid ground state with moderate magnetic frustration [26].…”

Raman fingerprints of fractionalized Majorana excitations in honeycomb iridate Ag$_3$LiIr$_2$O$_6$

“…This is owing to the intricate role of disorder present in these derived candidates which has been theoretically predicted to enhance the low energy density of states of the Majorana fermionic excitations [27,28]. Equating the upper cut off of ∼300 cm −1 of this broad Raman response to 3|J K | (J K is the Kitaev interaction strength), the theoretical estimate for the band edge of the Raman continuum from Majorana fermions [6], yields |J K | ≈ 12 meV which is in reasonable agreement with the Kitaev interaction strength obtained for this compound from recent density functional theoretical (DFT) calculations (J K ≈ 11.4 meV) [25].…”

Kitaev Magnetism through the Prism of Lithium Iridate

“…The problem of stacking disorder appears most prominently in that has been prepared with different amounts of stacking faults. Samples with a low concentration of stacking faults show long‐range magnetic order, [ 119,126,127 ] whereas samples with a high concentration of stacking faults develop a disordered magnetic state resembling a spin liquid. [ 93 ] This observation is in line with the previous work on pure α ‐ where magnetic ordering transition is also suppressed when the concentration of stacking faults increases.…”