7,936 research outputs found
The Friedmann equation in modified entropy-area relation from entropy force
According to the formal holographic principle, a modification to the
assumption of holographic principle in Verlinder's investigation of entropy
force is obtained. A more precise relation between entropy and area in the
holographic system is proposed. With the entropy corrections to the
area-relation, we derivate Newton's laws and Einstein equation with a static
spherically symmetric holographic screen. Furthermore we derived the correction
terms to the modified Friedmann equation of the FRW universe starting from the
holographic principle and the Debye model.Comment: Mod. Phys. Lett. A26, 489-500 (2011
Numerical simulations of a ballistic spin interferometer with the Rashba spin-orbital interaction
We numerically investigate the transport behavior of a quasi one-dimension
(1D) square loop device containing the Rashba spin-orbital interaction in the
presence of a magnetic flux. The conductance versus the magnetic field shows
the Al'tshuler-Aronov-Spivak (AAS) and Aharonov-Bohm (AB) oscillations. We
focus on the oscillatory amplitudes, and find that both of them are strongly
dependent on the spin precession angle (i.e. the strength of the spin-orbit
interaction) and exhibit no-periodic oscillations, which are well in agreement
with a recent experiment by Koga et al. [cond-mat/0504743(unpublished)].
However, our numerical results for the ideal 1D square loop device for the node
positions of the amplitudes of the AB and AAS oscillations are found to be of
some discrepancies comparing with quasi-1D square loop with a finite width. In
the presence of disorder and taking the disorder ensemble average, the AB
oscillation in the conductance will disappear, while the time-reversal
symmetric AAS oscillation still remains. Furthermore, the node positions of the
AAS oscillatory amplitude remains the same.Comment: 6 pages, 7 figure
Quantum simulation of exotic PT-invariant topological nodal loop bands with ultracold atoms in an optical lattice
Since the well-known PT symmetry has its fundamental significance and
implication in physics, where PT denotes the combined operation of
space-inversion P and time-reversal T, it is extremely important and intriguing
to completely classify exotic PT-invariant topological metals and to physically
realize them. Here we, for the first time, establish a rigorous classification
of topological metals that are protected by the PT symmetry using KO-theory. As
a physically realistic example, a PT-invariant nodal loop (NL) model in a 3D
Brillouin zone is constructed, whose topological stability is revealed through
its PT-symmetry-protected nontrivial Z2 topological charge. Based on these
exact results, we propose an experimental scheme to realize and to detect
tunable PT-invariant topological NL states with ultracold atoms in an optical
lattice, in which atoms with two hyperfine spin states are loaded in a
spin-dependent 3D OL and two pairs of Raman lasers are used to create
out-of-plane spin-flip hopping with site-dependent phase. Such a realistic
cold-atom setup can yield topological NL states, having a tunable ring-shaped
band-touching line with the two-fold degeneracy in the bulk spectrum and
non-trivial surface states. The states are actually protected by the combined
PT symmetry even in the absence of both P and T symmetries, and are
characterized by a Z2-type invariant (a quantized Berry phase). Remarkably, we
demonstrate with numerical simulations that (i) the characteristic NL can be
detected by measuring the atomic transfer fractions in a Bloch-Zener
oscillation; (ii) the topological invariant may be measured based on the
time-of-flight imaging; and (iii) the surface states may be probed through
Bragg spectroscopy. The present proposal for realizing topological NL states in
cold atom systems may provide a unique experimental platform for exploring
exotic PT-invariant topological physics.Comment: 11 pages, 6 figures; accepted for publication in Phys. Rev.
Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2
Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.Comment: 3 pages, 3 figure
Quark Mass Ratios in ChPT with the Difference of Quark Condensates Considered
The chiral effective Lagrangian for pseudoscalar nonet is constructed in
consideration of isospin breaking. And the difference of quark condensates is
taken accounted. The SU(3) singlet eta0 is not taken as Goldstone-boson. The
mixing with and without isospin symmetry is considered. The quark mass ratios
are obtained through solving the mass equations of mesons. We estimate the
change of quark mass ratios according to the change of the masses of pion+ and
kaon+ to see how the electromagnetic corrections affect our results. It turn
out that massless up quark is possible. The upper limit for mu/md is around
0.39. 2ms/(mu+md)=24.23~25.12. The values for quark condensate ratios and other
constants are limited in narrow ranges.Comment: 10 page
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