Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate Li2RuO3

Abstract

Li2RuO3 undergoes a structural transition at a relatively high temperature of 550 K with a distinct dimerization of Ru-Ru bonds on the otherwise isotropic honeycomb lattice. It exhibits a unique herringbone dimerization pattern with an unusually large value of bond shrinkage, about ~ 0.5 Å. However, many questions still remain about its origin and its effect on the physical properties. In this work, using high-quality single crystals we investigated the anisotropy of resistivity () and magnetic susceptibility () to find a very clear anisotropy: c* > b > a and b > a > c*. We also carried out density functional calculations for possible theoretical interpretations, and concluded that this anisotropic behavior is due to the correlation effects combined with the unique orbital structure and the dimerization of Ru 4d bands.

Revelation of Mott insulating state in layered honeycomb lattice Li2RuO3

“…These results exhibit an insulating ground state with the gap opening in the t 2g band; thus the E F has been set in the middle of the gap. This Mott gap has also been observed in the calculation using TB-mBJ [38] and LDA + cDMFT [32] calculations. The value of the energy gap of 0.84 eV is somewhat larger than other calculations [38] and as well as the activation gap (∼0.3 eV) from transport measurements [39].…”

Competing spin-orbital singlet states in the 4$d^4$ honeycomb ruthenate Ag$_3$LiRu$_2$O$_6$

“…S12 [18]). This contrasts with the systems with strong dimers where DFT calculations yield a band insulating ground state associated with molecular orbital formation [16,27,29]. These facts suggest that the weak dimers of the intermediate phase do not involve the formation of molecular orbitals.…”

Nonmagnetic $J = 0$ State and Spin-Orbit Excitations in K$_{2}$RuCl$_{6}$

“…A prominent example is an enigmatic nonmagnetic insulating state that was discovered in a variety of different compounds based on Ru 4+ ions (electron configuration 4d 4 ), which are expected to carry S = 1 spins according to Hund's rule. Models proposed to account for the nonmagnetism in these systems generally invoke quantum singlet formation in the spin degrees of freedom, such as exchange-coupled spin-1 chains with collective-singlet ground states [10] or spin-singlet dimers generated by orbital ordering [11][12][13][14]. However, singlet ground states can also be generated by the antiparallel alignment of the spin and orbital angular momenta promoted by the intra-atomic SOC [15].…”

“…Neutron scattering experiments on the antiferromagnetic Ru 4+ compound Ca 2 RuO 4 have indeed revealed a soft longitudinal magnon mode that has been interpreted as a hallmark of a proximate quantum phase transition into a SOC-driven singlet state [16]. In compounds with nonmagnetic ground states [10][11][12][13][14], however, materials issues (including especially the lack of sizeable, disorder-free single crystals for neutron experiments) have precluded spectroscopic measurements that could definitively resolve the origin of quantum singlet formation.…”

“…We have clearly revealed the J multiplet formation in the cubic crystal field environment, highlighting the unquenched orbital momenta actuated by the intraionic SOC. Existing descriptions of the singlet ground states in ruthenium magnets [10][11][12][13][14], however, tend to a priori assume spinonly S = 1 states with quenched orbital moment due to crystal field distortions, and generally neglect the role of SOC. Our result, on the contrary, suggests that the J multiplets are the generic starting point in the study of magnetism in Ru compounds and encourages reexamination of the theoretical description of the quantum singlet states in these materials.…”