Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4

Abstract

The spin-1=2 triangular lattice antiferromagnet YbMgGaO 4 has attracted attention recently as a quantum spin-liquid candidate with the possible presence of off-diagonal anisotropic exchange interactions induced by spin-orbit coupling. Whether a quantum spin liquid is stabilized or not depends on the interplay of various exchange interactions with chemical disorder that is inherent to the layered structure of the compound. We combine time-domain terahertz spectroscopy and inelastic neutron scattering measurements in the field-polarized state of YbMgGaO 4 to obtain better insight of its exchange interactions. Terahertz spectroscopy in this fashion functions as a high-field electron spin resonance and probes the spin-wave excitations at the Brillouin zone center, ideally complementing neutron scattering. A global spin-wave fit to all our spectroscopic data at fields over 4 T, informed by the analysis of the terahertz spectroscopy linewidths, yields constraints on the disorder-averaged g factors and exchange interactions. Our results paint YbMgGaO 4 as an easy-plane XXZ antiferromagnet with the combined and necessary presence of subleading next-nearest neighbor and weak anisotropic off-diagonal nearest-neighbor interactions. Moreover, the obtained g factors are substantially different from previous reports. This work establishes the hierarchy of exchange interactions in YbMgGaO 4 from high-field data alone and thus strongly constrains possible mechanisms responsible for the observed spin-liquid phenomenology.

YbMgGaO4: A Triangular‐Lattice Quantum Spin Liquid Candidate

“…The above experimentally determined Hamiltonian parameters are also largely consistent with the reported spin‐wave INS data measured by the other group at 7.8 T, J zz ≈ 0.15 meV, and J ± ≈ 0.1 meV . And the combined time‐domain terahertz spectroscopy and INS work basically complemented and confirmed the above INS results . While, they also proposed a significant second‐neighbor interaction, J 2 / J 1 ≈ 0.2 and J 2 ≈ 0.3 K, which is one order of magnitude larger than the aforementioned value of J 2 ≈ 0.03 K estimated from the dipole–dipole interaction.…”

“…And the combined time‐domain terahertz spectroscopy and INS work basically complemented and confirmed the above INS results . While, they also proposed a significant second‐neighbor interaction, J 2 / J 1 ≈ 0.2 and J 2 ≈ 0.3 K, which is one order of magnitude larger than the aforementioned value of J 2 ≈ 0.03 K estimated from the dipole–dipole interaction. However, the 4 f electrons of Yb 3+ ions in YbMgGaO 4 is highly localized in the real space (unlike 3 d electrons), and thus the second‐neighbor superexchange cannot make significant contribution to the magnetic couplings via the long‐distance “Yb( f )‐O( p )‐Yb( f )‐O( p )‐Yb( f )” virtual electron hopping processes.…”

“…Finally, refs. [] (may) suggest the importance of the second‐neighbor interaction ( J 2 ). While, J 2 should be very small in YbMgGaO 4 , J 2 ≈ 1.5% J 0 (see above), due to the high spatial localization of the 4 f electrons of the Yb 3+ ions.…”

Anisotropic field-induced ordering in the triangular-lattice quantum spin liquid NaYbSe2

“…So far, we do not have any estimate for these higher exchange terms. In the case of YbMgGaO 4 , these interactions are reported to be rather small [63]. Figures 6(a) and 6(b) represent the H-T phase diagrams for both H ⊥ c and H c directions, respectively, constructed from the field dependent C p (T ) and temperature dependent M (H) measurements [43].…”

Field-induced magnetic transition and spin fluctuations in the quantum spin-liquid candidate CsYbSe2

“…The heat capacity, magnetization, thermal conductivity, neutron scattering and muon spin relaxation find no transition in this compound and suggest a possible gapless QSL ground state [25][26][27][28][29][30][31][32]. However, the intrinsic Mg/Ga disorder exists between the frustrated layer and could induce the system to other state [25,29,30,[33][34][35][36]. Another classic 112 system ARQ 2 (A=Alkali metal, R=Rare-earth elements, Q = O, S, Se) was proposed as QSL candidate [37].…”