Related papers: Spin-dimer ground state driven by consecutive char…
We have investigated electronic structures of antiferromagnetic YBaCo_2O_5 using the local spin-density approximation (LSDA) + U method. The charge and orbital ordered insulating ground state is correctly obtained with the strong on-site…
Spin-state ordering - a periodic pattern of ions with different spin-state configurations along a crystal lattice - is a rare phenomenon, and its possible interrelation with other electronic degrees of freedom remains little explored. Here…
The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin…
The semiconductor-semiconductor transition of La2RuO5 is studied by means of augmented spherical wave (ASW) electronic structure calculations as based on density functional theory and the local density approximation. This transition has…
Alkali superoxides differ from conventional transition metal magnets, exhibit magnetism from partially occupied oxygen molecular $\pi^*$-orbitals. Among them, CsO$_2$ stands out for its potential to exhibit novel quantum collective…
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…
We study the competing phases and the phase transition phenomena in an effective spin-orbital coupled model derived for pyroxene titanium oxides ATiSi2O6 (A=Na, Li). Using the mean-field-type analysis and the numerical quantum transfer…
Akali superoxides AO2 (A=Na, K, Rb, Cs), due to an open p shell of the oxygen ion O2^- with degenerate pi orbitals, have spin and orbital degrees of freedom. The complex magnetic, orbital, and structural phase transitions observed…
Recent state-of-the-art crystallographic investigations of transition metal spinel compounds have revealed that the d- orbital charge carriers undergo ordering transitions with the formation of local "molecular bonding" units such as dimers…
Since the discovery of the Verwey transition in magnetite, transition metal compounds with pyrochlore structures have been intensively studied as a platform for realizing remarkable electronic phase transitions. We report the discovery of a…
We report a ground state with strongly coupled magnetic and charge density wave orders mediated via orbital ordering in the layered compound \tbt. In addition to the commensurate antiferromagnetic (AFM) and charge density wave (CDW) orders,…
We study \textit{ab initio} a pyrochlore compound, CsW$_{2}$O$_{6}$, which exhibits a yet unexplained metal-insulator transition. We find that (1) the reported low-$T$ structure is likely inaccurate and the correct structure has a twice…
Research on nickel-based superconductors has progressed from infinite-layer LaNiO$_2$ to finite-layer La$_{6}$Ni$_{5}$O$_{12}$, and most recently to the Ruddlesden-Popper phase La$_3$Ni$_2$O$_7$, which was found to exhibits onset of…
We suggest that the phase transition observed in NaV_2O_5 at T_c = 34K is not a spin-Peierls transition, but a charge ordering transition, related to the formal presence in this system of equal number of V^4+ and V^4- ions. Below T_c, V^4+…
We propose a scenario for the two phase transitions in $A$V$_2$O$_4$ ($A$=Zn, Mg, Cd), based on an effective spin-orbital model on the pyrochlore lattice. At high temperatures, spin correlations are strongly frustrated due to the lattice…
We present our theoretical results on the mechanism of two transitions in vanadium spinel oxides $A$V$_2$O$_4$ ($A$=Zn, Mg, or Cd) in which magnetic V cations constitute a geometrically-frustrated pyrochlore structure. We have derived an…
The metal-insulator transition of the Magneli phase Ti4O7 is studied by means of augmented spherical wave (ASW) electronic structure calculations as based on density functional theory and the local density approximation. The results show…
Evolution of composite spin-orbital order and coupled spin-orbital excitations is studied in a variety of $d^4$ systems with $n$=$4$ electrons in the $t_{2g}$ orbital sector using the generalised self-consistent + fluctuations approach for…
Recent measurements on MgV$_2$O$_4$ single crystal have reignited the debate on the role of spin-orbit (SO) coupling in dictating the orbital order in Vanadium spinel systems. Density functional theory calculations were performed using the…
Based on the refined crystal structure comprised of columns of 3*4 planar blocks of NbO6 octahedra and first principles electronic structure methods, we find that orthorhombic (o)-Nb$_{12}$O$_{29}$ introduces a new class of transition metal…