Spin-orbital-entangled quantum magnet on a honeycomb lattice
Invited
Abstract
In heavy transition-metal compounds containing 4d or 5d elements, strong spin-orbit coupling often yields spin-orbital-entangled Jeff-states for d-electrons. The magnetic interactions between such states may give rise to an exotic ground state due to their bond-sensitive character. In particular, quantum liquid state of spin-orbital-entangled objects have been expected to emerge in a simple honeycomb lattice.
Honeycomb-based iridates with Jeff = 1/2 pseudospins have been intensively investigated as a potential realization of Kitaev spin liquid. Although the honeycomb iridates such as Na2IrO3 and α-Li2IrO3 are shown to undergo magnetic ordering likely due to the additional magnetic interactions other than Kitaev-type exchange, a quantum liquid state has been identified in the hydrogen-exchanged material H3LiIr2O6. No magnetic order or spin-glass freezing is not seen in H3LiIr2O6 down to 50 mK. However, clear evidence for Kitaev-type spin liquid is lacking so far, and the prime driving force for the liquid state remains elusive. In order to investigate the critical role of hydrogen, we synthesized an isotopic material D3LiIr2O6. D3LiIr2O6 displays a large isotope effect in structural and magnetic properties; the antiferromagnetic Weiss temperature increases from 100 K for H3LiIr2O6 to 170 K for D3LiIr2O6. Nevertheless, the quantum liquid state was found to be robust. We argue that the disordered OH/OD bonds likely play a role to stabilize the quantum liquid state.
Another exotic honeycomb magnet is expected for systems with d4 configuration. In the case, the spin-orbit coupling produces nonmagnetic Jeff = 0 singlet ground state. However, the d4 ions magnetically interact with each other via the excited Jeff = 1 levels, and such magnetic interactions are also shown to inherit bond-dependent character. We argue that a honeycomb ruthenate Ag3LiRu2O6 has the spin-orbit induced singlet ground state and discuss the possible pressure-induced electronic phase transitions.
Honeycomb-based iridates with Jeff = 1/2 pseudospins have been intensively investigated as a potential realization of Kitaev spin liquid. Although the honeycomb iridates such as Na2IrO3 and α-Li2IrO3 are shown to undergo magnetic ordering likely due to the additional magnetic interactions other than Kitaev-type exchange, a quantum liquid state has been identified in the hydrogen-exchanged material H3LiIr2O6. No magnetic order or spin-glass freezing is not seen in H3LiIr2O6 down to 50 mK. However, clear evidence for Kitaev-type spin liquid is lacking so far, and the prime driving force for the liquid state remains elusive. In order to investigate the critical role of hydrogen, we synthesized an isotopic material D3LiIr2O6. D3LiIr2O6 displays a large isotope effect in structural and magnetic properties; the antiferromagnetic Weiss temperature increases from 100 K for H3LiIr2O6 to 170 K for D3LiIr2O6. Nevertheless, the quantum liquid state was found to be robust. We argue that the disordered OH/OD bonds likely play a role to stabilize the quantum liquid state.
Another exotic honeycomb magnet is expected for systems with d4 configuration. In the case, the spin-orbit coupling produces nonmagnetic Jeff = 0 singlet ground state. However, the d4 ions magnetically interact with each other via the excited Jeff = 1 levels, and such magnetic interactions are also shown to inherit bond-dependent character. We argue that a honeycomb ruthenate Ag3LiRu2O6 has the spin-orbit induced singlet ground state and discuss the possible pressure-induced electronic phase transitions.
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Presenters
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Tomohiro Takayama
Max Planck Inst, University of Tokyo
Authors
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Tomohiro Takayama
Max Planck Inst, University of Tokyo