180 research outputs found
Quantum Many-Body Calculation of Mixed-Parity Pairing in the Sr2RuO4 Superconductor Induced by Spin-Orbit Coupling
The unusual superconducting state in Sr2RuO4 has long been viewed as being analogous to a superfluid state in liquid 3He. Nevertheless, calculations based on this odd-parity state are presently unable to completely reconcile the properties of Sr2RuO4. Using a self-consistent quantum many-body scheme that employs realistic parameters, we are able to model several signature properties of the normal and superconducting states of Sr2RuO4. We find that the dominant component of the model superconducting state is of even parity and closely related to superconducting state for the high-Tc cuprates although a smaller odd-parity component is induced by spin-orbit coupling. This mixed pairing state gives a more complete representation of the complex phenomena measured in Sr2RuO4
Reconstruction of thermally-symmetrized quantum autocorrelation functions from imaginary-time data
In this paper, I propose a technique for recovering quantum dynamical
information from imaginary-time data via the resolution of a one-dimensional
Hamburger moment problem. It is shown that the quantum autocorrelation
functions are uniquely determined by and can be reconstructed from their
sequence of derivatives at origin. A general class of reconstruction algorithms
is then identified, according to Theorem 3. The technique is advocated as
especially effective for a certain class of quantum problems in continuum
space, for which only a few moments are necessary. For such problems, it is
argued that the derivatives at origin can be evaluated by Monte Carlo
simulations via estimators of finite variances in the limit of an infinite
number of path variables. Finally, a maximum entropy inversion algorithm for
the Hamburger moment problem is utilized to compute the quantum rate of
reaction for a one-dimensional symmetric Eckart barrier.Comment: 15 pages, no figures, to appear in Phys. Rev.
Quasiparticle Band Structure and Density Functional Theory: Single-Particle Excitations and Band Gaps in Lattice Models
We compare the quasiparticle band structure for a model insulator obtained
from the fluctuation exchange approximation (FEA) with the eigenvalues of the
corresponding density functional theory (DFT) and local density approximation
(LDA). The discontinuity in the exchange-correlation potential for this model
is small and the FEA and DFT band structures are in good agreement. In contrast
to conventional wisdom, the LDA for this model overestimates the size of the
band gap. We argue that this is a consequence of an FEA self-energy that is
strongly frequency dependent, but essentially local.Comment: 8 pages, and 5 figure
Shadow features and shadow bands in the paramagnetic state of cuprate superconductors
The conditions for the precursors of antiferromagnetic bands in cuprate
superconductors are studied using weak-to-intermediate coupling approach. It is
shown that there are, in fact, three different precursor effects due to the
proximity to antiferromagnetic instability: i) the shadow band which associated
with new pole in the Green's function ii) the dispersive shadow feature due to
the thermal enhancement of the scattering rate and iii) the non-dispersive
shadow feature due to quantum spin fluctuation that exist only in
scan of the spectral function . I found
that dispersive shadow peaks in can exist at finite
temperature T in the renormalized classical regime, when ,
( is the characteristic energy of
spin fluctuations, is the thermal wave length of electron). In
contrast at zero temperature, only non-dispersive shadow feature in has been found. I found, however, that the latter
effect is always very small. The theory predict no shadow effects in the
optimally doped materials. The conditions for which shadow peaks can be
observed in photoemission are discussed.Comment: 6 pages, REVTEX, 2 ps figures, version to be published in PR
Optical Absorption of CuO antiferromagnetic chains at finite temperatures
We use a high-statistic quantum Monte Carlo and Maximum Entropy
regularization method to compute the dynamical energy correlation function
(DECF) of the one-dimensional (1D) antiferromagnetic Heisenberg model
at finite temperatures. We also present a finite temperature analytical ansatz
for the DECF which is in very good agreement with the numerical data in all the
considered temperature range. From these results, and from a finite temperature
generalisation of the mechanism proposed by Lorenzana and Sawatsky [Phys. Rev.
Lett. {\bf 74}, 1867 (1995)], we compute the line shape for the optical
absorption spectra of multimagnon excitations assisted by phonons for quasi 1D
compounds. The line shape has two contributions analogous to the Stokes and
anti-Stokes process of Raman scattering. Our low temperature data is in good
agreement with optical absorption experiments of CuO chains in
SrCuO. Our finite temperature results provide a non trivial prediction
on the dynamics of the Heisenberg model at finite temperatures that is easy to
verify experimentally.Comment: 7 pages, 5 figure
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