Related papers: The Jahn-Teller theorem for 3d ions and their comp…
The Kugel-Khomskii Hamiltonian for cubic titanates describes spin and orbital superexchange interactions between $d^1$ ions having three-fold degenerate $t_{2g}$ orbitals. Since orbitals do not couple along "inactive" axes, perpendicular to…
At 750K, LaMnO_3 has a cooperative Jahn-Teller (JT) distortion, with Mn atoms in distorted oxygen octahedra. This lifts the degeneracy of the singly-occupied $e_g$ orbitals of the Mn$^{3+}$ ions, which then become orbitally ordered. We use…
We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites…
Cubic to tetragonal distortion in spinel compounds have been a contentious issue for last two decades. Different groups have proposed different mechanisms to understand such a distortion in these spinels, which are: (i) spin lattice…
The interplay between spin and orbital degrees of freedom gives rise to a variety of emergent phases in correlated 4d and 5d transition-metal systems. Strong spin-orbit coupling (SOC) significantly alters Jahn-Teller (JT) physics, often…
MgV$_{2}$O$_{4}$ is a spinel based on magnetic V$^{3+}$ ions which host both spin ($S=1$) and orbital ($l_{eff}=1$) moments. Owing to the underlying pyrochlore coordination of the magnetic sites, the spins in MgV$_{2}$O$_{4}$ only…
Motivated by the absence of cooperative Jahn-Teller effect and of magnetic ordering in LiNiO$_2$, a layered oxide with triangular planes, we study a general spin-orbital model on the triangular lattice. A mean-field approach reveals the…
Theory of $\tilde{J}$-pseudospin for $f$ element in cubic environment is developed. By fulfilling the symmetry requirements and the adiabatic connection to atomic limit, the crystal-field states are uniquely transformed into…
We derive a spin-orbital model for insulating LaMnO_3 which fulfills the SU(2) symmetry of S=2 spins at Mn^{3+} ions. It includes the complete e_g and t_{2g} superexchange which follows from a realistic Mn^{2+} multiplet structure in cubic…
Temperature dependences of a magnetic and an orbital Bragg reflection at the Mn L2 and L3 edges of La0.5Sr1.5MnO4 have been collected. The temperature evolution of the orbital reflection depend strongly on the x-ray energy and reflects the…
The orbital degree of freedom in rare-earth nickelates is typically inactive across the temperature-driven metal-insulator transition, where the system develops two inequivalent Ni sites associated with Ni-O bond disproportionation and…
We calculate the magnetic susceptibility and g-factor of the isolated C_{60}^- ion at zero temperature, with a proper treatment of the dynamical Jahn-Teller effect, and of the associated orbital angular momentum, Ham-reduced gyromagnetic…
We present measurements of the magnetic susceptibility and of the thermal expansion of a LaCoO$_3$ single crystal. Both quantities show a strongly anomalous temperature dependence. Our data are consistently described in terms of a…
Compared to isolated C$_{60}^{3-}$ ions, characterized by a threedimensional equipotential trough at the bottom of the lowest adiabatic potential energy surface (APES), the Jahn-Teller (JT) effect in cubic fullerides is additionally…
The role of elastic interactions between Jahn-Teller ions in formation of various orbital- and charge-ordered structures in manganites and related compounds is analyzed. It is shown that such interactions alone are often sufficient to…
To clarify a crucial role of a spin-orbit coupling in the emergence of novel spin-orbital states in $5d$-electron compounds such as Sr$_{2}$IrO$_{4}$, we investigate ground state properties of a $t_{\rm 2g}$-orbital Hubbard model on a…
We present a comprehensive structural study on perovskite-type 6H-Ba3CuSb2O9, which exhibits a spin-orbital short-range ordering on a honeycomb-based lattice. By combining synchrotron x-ray diffraction, electron spin resonance, ultrasound…
When spin-orbit-entangled $d$-electrons reside on a honeycomb lattice, rich quantum states are anticipated to emerge, as exemplified by the $d^5$ Kitaev materials. Distinct yet equally intriguing physics may be realized with a $d$-electron…
We derive an effective Hamiltonian that takes into account the quantum nature of phonons and models cooperative Jahn-Teller effect in the adiabatic regime and at strong electron-phonon coupling in one dimension. Our approach involves…
We have calculated the discrete low-energy electronic structure in LaMnO3 originating from the atomic-like states of the strongly correlated 3d4 electronic system occurring in the Mn3+ ion. We take into account very strong intra-atomic…