13,749 research outputs found

### Optical phonons in new ordered perovskite Sr2Cu(Re0.69Ca0.31) Oy system observed by infrared reflectance spectroscopy

We report infrared reflectivity spectra for a new correlated cupric oxide
system Sr2Cu(Re0.69Ca0.31)Oy with y ~ 0.6 at several temperatures ranging
between 8 and 380 K. The reflectivity spectrum at 300 K comprises of several
optical phonons. A couple of residual bands located around 315 and 653 cm-1
exhibit exceptionally large intensity as compared to the other ones. The
overall reflectivity spectrum lifts up slightly with increasing temperature.
The energy and damping factor of transverse-optical phonons are determined by
fitting the imaginary dielectric constant by Lorentz oscillator model and
discussed as a function of temperature in terms of lattice anharmonicity.Comment: 9 pages, 3 figures, presented at ISS2005, to appear in Physica

### The energetics of giant radio galaxy lobes from inverse Compton scattering observations

Giant radio galaxy (GRG) lobes are excellent laboratories to study the
evolution of the particle and B-field energetics. However, these results are
based on assumptions of the shape and extension of the GRG lobe electron
spectrum. We re-examine the energetics of GRG lobes as derived by inverse
Compton scattering of CMB photons (ICS-CMB) by relativistic electrons in RG
lobes to assess the physical conditions of RG lobes, their energetics and their
radiation regime. We consider the GRG DA 240 recently observed by Suzaku as a
reference case and we also discuss other RG lobes observed with Chandra and
XMM. We model the spectral energy distribution of the DA 240 East lobe to get
constraint on the shape and the extension of the electron spectrum in the lobe
by using multi-frequency information from radio to gamma-rays. We use radio and
X-ray data to constrain the shape and normalization of the electron spectrum
and we then calculate the SZ effect expected in GRG lobes that is sensitive to
the total electron energy density. We show that the electron energy density U_e
derived form X-ray observations yields only a rough lower limit to its actual
value and that most of the estimates of U_e based on X-ray measurements have to
be increased even by a large factor by considering realistic estimates of the
lower electron momentum p_1. This brings RG lobes away from the equipartition
condition towards a particle-dominated and Compton power dominance regime. We
use the distribution of RG lobes in the U_e/U_B vs. U_e/U_CMB plane as a
further divide between different physical regimes of particle and field
dominance, and radiation mechanism dominance in RG lobes. We conclude that the
SZ effect produced by ICS-CMB mechanism observable in RG lobes provides
reliable estimate of p_1 and U_e and is the best tool to determine the total
energy density of RG lobes and to assess their physical regime.Comment: 9 pages, 6 figures, A&A in pres

### New quantum critical points of $j=3/2$ Dirac electrons in antiperovskite topological crystalline insulators

We study the effect of the long-range Coulomb interaction in $j=3/2$ Dirac
electrons in cubic crystals with the $O_h$ symmetry, which serves as an
effective model for antiperovskite topological crystalline insulators. The
renormalization group analysis reveals three fixed points that are Lorentz
invariant, rotationally invariant, and $O_h$ invariant. Among them, the
Lorentz- and $O_h$-invariant fixed points are stable in the low-energy limit
while the rotationally invariant fixed point is unstable. The existence of a
stable $O_h$-invariant fixed point of Dirac fermions with finite velocity
anisotropy presents an interesting counterexample to emergent Lorentz
invariance in solids.Comment: 5 pages, 3 figure

### Theory of interacting topological crystalline insulators

We study the effect of electron interactions in topological crystalline
insulators (TCIs) protected by mirror symmetry, which are realized in the SnTe
material class and host multi-valley Dirac fermion surface states. We find that
interactions reduce the integer classification of noninteracting TCIs in three
dimensions, indexed by the mirror Chern number, to a finite group $Z_8$. In
particular, we explicitly construct a microscopic interaction Hamiltonian to
gap 8 flavors of Dirac fermions on the TCI surface, while preserving the mirror
symmetry. Our construction builds on interacting edge states of $U(1)\times
Z_2$ symmetry-protected topological (SPT) phases of fermions in two dimensions,
which we classify. Our work reveals a deep connection between 3D topological
phases protected by spatial symmetries and 2D topological phases protected by
internal symmetries.Comment: v2. 10 pages, 3 figures. Added new materials and improved
presentatio

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