Spin-orbit-entangled electronic phases in 4$d$ and 5$d$ transition-metal compounds

Abstract

Complex oxides with 4d and 5d transition-metal ions recently emerged as a new paradigm in correlated electron physics, due to the interplay between spin-orbit coupling and electron interactions. For 4d and 5d ions, the spin-orbit coupling, ζ, can be as large as 0.2-0.4 eV, which is comparable with and often exceeds other relevant parameters such as Hund's coupling JH, noncubic crystal field splitting ∆, and the electron hopping amplitude t. This gives rise to a variety of spin-orbitentangled degrees of freedom and, crucially, non-trivial interactions between them that depend on the d-electron configuration, the chemical bonding, and the lattice geometry. Exotic electronic phases often emerge, including spin-orbit assisted Mott insulators, quantum spin liquids, excitonic magnetism, multipolar orderings and correlated topological semimetals. This paper provides a selective overview of some of the most interesting spin-orbit-entangled phases that arise in 4d and 5d transition-metal compounds.

Kitaev Spin Liquid in 3d Transition Metal Compounds

“…After decades of tremendous efforts, the conceptual understanding of QSL state has been gradually advanced. However, the concern of whether the QSL could really occur in real physical system has not been finally dispelled until 2006 when Kitaev proposed his honeycomb model 4 with an exact solution and a stable gapless QSL ground state; for extensive discussions of this model, see the recent reviews 5,6,7,8,9,10,11 .…”

Extremely Large Magnetoresistance in the Hourglass Dirac Loop Chain Metal β-ReO2

“…A wide variety of physical properties appear in 5d transition metal compounds owing to competition and cooperation between the spin-orbit interactions (SOIs) as large as 0.4 eV, crystal fields, and electron correlations. 1) Recent extensive materials investigations revealed the novel electronic properties of 5d compounds. 2,3) Particularly observed in rhenium compounds are superconductivity in Cd2Re2O7 and HgxReO3, [4][5][6][7] multipole orders in Cd2Re2O7 and Ba2MgReO6, [8][9][10][11][12] half-metallic states above room temperature in A2BReO6, 13,14) pleochroism in Ca3ReO5Cl2, 15) and frustrated magnetism in A3ReO5Cl2.…”

Crystal-field excitations and vibronic modes in triangular-lattice spin-liquid candidate TbInO$_3$

“…bi-pyramids and buckling the Tb layers [30]. Because of the tilting, the apex oxygen sites O (1) and O (2) , and the planer oxygen sites O (3) and O (4) become non-equivalent; as a result of the buckling, Tb (1) site becomes slightly out of the plane formed by Tb (2) . The unit cell contains six formula units.…”

“…Interplay between electron correlation and spin-orbit coupling (SOC) gives rise to a variety of emergent quantum phases and transitions [1]. Especially, because of the compactness of f orbits and the heaviness of f elements, f -electron systems are in both the strong Mott regime and the strong SOC regime [2].…”