12,741 research outputs found
Effects of the Spin-Orbit Coupling and the Superconductivity in simple-cubic alpha-Polonium
We have investigated the mechanism of stabilizing the simple-cubic (SC)
structure in polonium (alpha- Po), based on the phonon dispersion calculations
using the first-principles all-electron band method. We have demonstrated that
the stable SC structure results from the suppression of the Peierls instability
due to the strong spin-orbit coupling (SOC) in alpha-Po. Further, we have
explored the possible superconductivity in alpha-Po, and predicted that it
becomes a superconductor with Tc ~ 4 K. The transverse soft phonon mode at q ~
2/3 R, which is greatly influenced by the SOC, plays an important role both in
the structural stability and the superconductivity in alpha-Po. We have
discussed effects of the SOC and the volume variation on the phonon dispersions
and superconducting properties of alpha-Po.Comment: 5pages, 5figure
Pressure-induced Phonon Softenings and the Structural and Magnetic Transitions in CrO
To investigate the pressure-induced structural transitions of chromium
dioxide (CrO), phonon dispersions and total energy band structures are
calculated as a function of pressure. The first structural transition has been
confirmed at P 10 GPa from the ground state tetragonal CrO
(t-CrO) of rutile type to orthorhombic CrO (o-CrO) of
CaCl type. The half-metallic property is found to be preserved in
o-CrO. The softening of Raman-active B phonon mode, which is
responsible for this structural transition, is demonstrated. The second
structural transition is found to occur for P 61.1 GPa from ferromagnetic
(FM) o-CrO to nonmagnetic (NM) monoclinic CrO (m-CrO) of
MoO type, which is related to the softening mode at {\bf q} =
R(1/2,0,1/2). The third structural transition has been newly identified at P=
88.8 GPa from m-CrO to cubic CrO of CaF type that is a FM
insulator
A study on the turbulent transport of an advective nature in the fluid plasma
Advective nature of the electrostatic turbulent flux of plasma energy is
studied numerically in a nearly adiabatic state. Such a state is represented by
the Hasegawa-Mima equation that is driven by a noise that may model the
destabilization due to the phase mismatch of the plasma density and the
electric potential. The noise is assumed to be Gaussian and not to be invariant
under reflection along a direction . It is found that the flux density
induced by such noise is anisotropic: While it is random along , it is
not along the perpendicular direction and the flux is not
diffusive. The renormalized response may be approximated as advective with the
velocity being proportional to in the Fourier space
Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO
To explore the driving mechanisms of the metal-insulator transition (MIT) and
the structural transition in VO2, we have investigated phonon dispersions of
rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band
calculations. We have found that the phonon softening instabilities occur in
both cases, but the softened phonon mode only in the DFT+U describes properly
both the MIT and the structural transition from R-VO2 to monoclinic VO2
(M1-VO2). This feature demonstrates that the Coulomb correlation effect plays
an essential role of assisting the Peierls transition in R-VO2. We have also
found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable
under high pressure. We have predicted a new phase of VO2 at high pressure that
has a monoclinic CaCl2-type structure with metallic nature
- β¦