Related papers: Octahedral rotation instability in Ba$_2$IrO$_4$
We report the structural and magnetic properties of the 4}\textit{\textcolor{black}{d }}\textcolor{black}{(M = Rh) based and 5}\textit{\textcolor{black}{d }}\textcolor{black}{(M = Ir) based systems Ba$_{3}$M$_{x}$Ti$_{3-x}$O$_{9}$…
Among the phases of SiO2 are alpha and beta cristobalites, which have a long and somewhat controversial history of proposed structural assignments and phase-transition mechanisms. Recently, Zhang and Scott found new indications that the…
The back-bending phenomenon for compact stars is studied by means of analytical equations of state, for both constant-pressure phase transitions and the transitions through the mixed-phase region. We restrict ourselves to the case of normal…
Let $\Omega_0$ denote the unit ball of $\mathbb{R}^N$ ($N\ge 2$) centered at the origin. We suppose that $\Omega_0$ contains a core, given by a smaller concentric ball $D_0$, made of a (possibly) different material. We discover that,…
We present a detailed study of the electronic and magnetic interactions of Ba2CoO4, structurally very uncommon because of the isolated CoO4 distorted tetrahedral coordination. We show the presence of Co(d)-O(p) hybridized states…
Molybdenum borides were studied theoretically using first-principles calculations, empirical total energy model and global optimization techniques to determine stable crystal structures. Our calculations reveal the structures of known Mo-B…
Neutron scattering studies on powder and single crystals have provided new evidences for unconventional magnetism in Cu2Te2O5Cl2. The compound is built from tetrahedral clusters of S=1/2 Cu2+ spins located on a tetragonal lattice. Magnetic…
We report a single-crystal neutron diffraction study of the layered $\rm Sr_2IrO_4$. This work unambiguously determines the magnetic structure of the system and reveals that the spin orientation rigidly tracks the staggered rotation of the…
Distortions of the oxygen octahedra influence the fundamental electronic structure of perovskite oxides, such as their bandwidth and exchange interactions. Utilizing a fully ab-initio methodology based on density functional theory plus…
The magnetic properties of the pyrochlore iridate material Eu$_2$Ir$_2$O$_7$ (5$d^5$) have been studied based on the first principle calculations, where the crystal field splitting $\Delta$, spin-orbit coupling (SOC) $\lambda$ and Coulomb…
We studied the crystal and magnetic structure of Ca2RuO4 by different diffraction techniques under high pressure. The observed first order phase transition at moderate pressure (0.5 GPa) between the insulating phase and the metallic high…
The three-dimensional nature of plasmoid instabilities is studied using the reduced magnetohydrodynamic equations. For a Harris equilibrium with guide field, represented by $\vc{B}_o = B_{po} \tanh (x/\lambda) \hat{y} + B_{zo} \hat{z}$, a…
Using first-principles methods, we predict the energy landscape and ferroelectric states of double perovskites of the form AA$'$BB$'$O$_6$ in which the atoms on both the A and B sites are arranged in rock-salt order. While we are not aware…
Incoherent bremsstrahlung by high-energy particles in crystal is due to the thermal spread of atoms in relation to their equilibrium positions in the lattice. The simulation procedure developed earlier for the incoherent radiation is…
We generalize recent study of the stability of isotropic (spherical) rotating membranes to the anisotropic ellipsoidal membrane. We find that while the stability persists for deformations of spin $l=1$, the quadrupole and higher spin…
Our first-principles computations show that the ground state of PbTiO$_3$ under hydrostatic pressure transforms discontinuously from $P4mm$ to $R3c$ at 9 GPa. Spontaneous polarization decreases with increasing pressure so that the $R3c$…
Emergent phenomena arising from the collective behavior of electrons is generally expected when Coulomb interactions dominate over the kinetic energy, as in delocalized quasiparticles in highly degenerate flat bands. Bernal-stacked bilayer…
The chemical, structural, mechanical, and dynamical stabilities of the $\alpha$- and $\beta$-Ga$_2$O$_3$ are confirmed from respective negative formation energies, negative cohesive energies, favorable elastic constants, and positive phonon…
For a high-quality single crystal of UPd_3 we present the relevant elastic constants and ultrasonic attenuation data. In addition to the magnetic phase transition at T_2=4.4 +/- 0.1K and the quadrupolar transition at T_1~6.8K, we find…
While performing molecular dynamics simulations of a simple monatomic liquid, we observed the crystallization of a material displaying octagonal symmetry in its simulated diffraction pattern. Inspection of the atomic arrangements in the…