705 research outputs found
Band Distributions for Quantum Chaos on the Torus
Band distributions (BDs) are introduced describing quantization in a toral
phase space. A BD is the uniform average of an eigenstate phase-space
probability distribution over a band of toral boundary conditions. A general
explicit expression for the Wigner BD is obtained. It is shown that the Wigner
functions for {\em all} of the band eigenstates can be reproduced from the
Wigner BD. Also, BDs are shown to be closer to classical distributions than
eigenstate distributions. Generalized BDs, associated with sets of adjacent
bands, are used to extend in a natural way the Chern-index characterization of
the classical-quantum correspondence on the torus to arbitrary rational values
of the scaled Planck constant.Comment: 12 REVTEX page
Average ground-state energy of finite Fermi systems
Semiclassical theories like the Thomas-Fermi and Wigner-Kirkwood methods give
a good description of the smooth average part of the total energy of a Fermi
gas in some external potential when the chemical potential is varied. However,
in systems with a fixed number of particles N, these methods overbind the
actual average of the quantum energy as N is varied. We describe a theory that
accounts for this effect. Numerical illustrations are discussed for fermions
trapped in a harmonic oscillator potential and in a hard wall cavity, and for
self-consistent calculations of atomic nuclei. In the latter case, the
influence of deformations on the average behavior of the energy is also
considered.Comment: 10 pages, 8 figure
On Using Taylor's Hypothesis for Three-Dimensional Mixing Layers
In the present study, errors in using Taylor's hypothesis to transform measurements obtained in a temporal (or phase) frame onto a spatial one were evaluated. For the first time, phase-averaged ('real') spanwise and streamwise vorticity data measured on a three-dimensional grid were compared directly to those obtained using Taylor's hypothesis. The results show that even the qualitative features of the spanwise and streamwise vorticity distributions given by the two techniques can be very different. This is particularly true in the region of the spanwise roller pairing. The phase-averaged spanwise and streamwise peak vorticity levels given by Taylor's hypothesis are typically lower (by up to 40%) compared to the real measurements
Crystal properties of eigenstates for quantum cat maps
Using the Bargmann-Husimi representation of quantum mechanics on a torus
phase space, we study analytically eigenstates of quantized cat maps. The
linearity of these maps implies a close relationship between classically
invariant sublattices on the one hand, and the patterns (or `constellations')
of Husimi zeros of certain quantum eigenstates on the other hand. For these
states, the zero patterns are crystals on the torus. As a consequence, we can
compute explicit families of eigenstates for which the zero patterns become
uniformly distributed on the torus phase space in the limit . This
result constitutes a first rigorous example of semi-classical equidistribution
for Husimi zeros of eigenstates in quantized one-dimensional chaotic systems.Comment: 43 pages, LaTeX, including 7 eps figures Some amendments were made in
order to clarify the text, mainly in the 4 first sections. Figures are
unchanged. To be published in: Nonlinearit
NMR study of electronic correlations in Mn-doped Ba(Fe 1 − x Co x ) 2 As 2 and BaFe 2 (As 1 − x P x ) 2
International audienceWe probe the real space electronic response to a local magnetic impurity in isovalent and het-erovalent doped BaFe2As2 (122) using Nuclear Magnetic Resonance (NMR). The local moments carried by Mn impurities doped into Ba(Fe1−xCox)2As2 (Co-122) and BaFe2(As1−xPx)2 (P-122) at optimal doping induce a spin polarization in the vicinity of the impurity. The amplitude, shape and extension of this polarisation is given by the real part of the susceptibility χ (r) of FeAs layers, and is consequently related to the nature and strength of the electronic correlations present in the system. We study this polarisation using 75 As NMR in Co-122 and both 75 As and 31 P NMR in P-122. The NMR spectra of Mn-doped materials is made of two essential features. First is a satellite line associated with nuclei located as nearest neighbor of Mn impurities. The analysis of the temperature dependence of the shift of this satellite line shows that Mn local moments behave as isolated Curie moments. The second feature is a temperature dependent broadening of the central line. We show that the broadening of the central line follows the susceptibility of Mn local moments, as expected from typical RKKY-like interactions. This demonstrates that the susceptibility χ (r) of FeAs layers does not make significant contribution to the temperature dependent broadening of the central line. χ (r) is consequently only weakly temperature dependent in optimally doped Co-122 and P-122. This behaviour is in contrast with that of strongly correlated materials such as under-doped cuprate high-Tc superconductors where the central line broadens faster than the impurity susceptibility grows, because of the development of strong magnetic correlations when T is lowered. Moreover, the FeAs layer susceptibility is found quantitatively similar in both heterovalent doped and isolvalent doped BaFe2As2
Reply to Comment by Borisenko et al. on article `A de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs'
Recently, Borisenko et al have posted a Comment (arXiv:1108.1159) where they
suggest an alternative interpretation of our de Haas-van Alphen (dHvA)
measurements on the superconductor LiFeAs. In our original paper
(arXiv:1107.4375) we concluded that our measurements of the bulk Fermi surface
were not consistent with the surface bands observed thus far by ARPES.
Borisenko et al dispute this and suggest the two measurements are consistent if
some of the orbits we observe are due to magnetic breakdown. We argue here that
this scenario is inconsistent with the experimental data and therefore that our
original conclusion stands.Comment: 4 pages with figure
de Haas-van Alphen oscillations in the underdoped cuprate YBaCuO
The de Haas-van Alphen effect was observed in the underdoped cuprate
YBaCuO via a torque technique in pulsed magnetic fields up to
59 T. Above an irreversibility field of 30 T, the magnetization exhibits
clear quantum oscillations with a single frequency of 540 T and a cyclotron
mass of 1.76 times the free electron mass, in excellent agreement with
previously observed Shubnikov-de Haas oscillations. The oscillations obey the
standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic
observation of quantum oscillations confirms the existence of a well-defined,
close and coherent, Fermi surface in the pseudogap phase of cuprates.Comment: published versio
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