Orbital Correlations in Monolayer Manganites - From Spin t-J Model to Orbital t-J Model

Abstract

On the example of monolayer manganites we show that the theoretical ideas developed long ago along the derivation of the spin t−J model from the Hubbard model are nowadays very helpful in strongly correlated oxides with partly filled degenerate orbitals. We analyze a realistic orbital t−J model for eg electrons in La1−xSr1+xMnO4 monolayer manganites, and discuss the evolution of spin and orbital correlations under increasing doping by performing exact diagonalization of finite clusters, with electronic kinetic energy determined self-consistently at a finite temperature by classical Monte Carlo for t2g spins. Several experimental results are reproduced. Spin t−J modelA new perspective to treat strongly correlated electrons was opened by the derivation of the spin t−J model three decades ago [1]. We argue that this derivation opened new routes to understand the complex magnetic and superconducting instabilities in the Hubbard model, and proved to be a very useful paradigm in strongly correlated electron systems. At that time it was already realized that the Hubbard model,where a † iσ is an electron creation operator in spin state σ =↑, ↓ at site i and U is local Coulomb interaction, is perfectly designed to describe electron localization (497)

Charge and Orbital Order in Transition Metal Oxides

“…This motivates two questions in the theory: (i) whether orbital excitations could couple to the moving hole and generate as well a new energy scale, as the hole-magnon coupling does, and (ii) whether spin--orbital entanglement has any important consequences for the hole dynamics. Both of them were addressed in the orbital t-J model for e g electrons [119], and in the analogous models for t 2g orbitals developed recently, see below.…”

Spin-Orbital Physics in Transition Metal Oxides

“…Similar to doped manganites [61], also in doped R 1−x (Sr,Ca) x VO 3 systems orbital order gradually disappears [62]. The composite C-AF/G-AO order survives, however, is a broad range of doping, in contrast to La 1−x Sr x MnO 3 , where FM order sets in already at x ∼ 0.10.…”

Charge and orbital order in transition metal oxides

“…This motivates two questions in the theory: (i) whether orbital excitations could couple as well to the moving hole and generate a new energy scale, as the magnons do, and (ii) whether spin-orbital entanglement has any important consequences for the hole dynamics. Both of them were addressed in the orbital t-J model for e g electrons [117], and in the analogous models for t 2g orbitals developed recently, see below.…”