2,745 research outputs found
Superconductivity and Pseudogap in Quasi-Two-Dimensional Metals around the Antiferromagnetic Quantum Critical Point
Spin fluctuations (SF) and SF-mediated superconductivity (SC) in
quasi-two-dimensional metals around the antiferrromagnetic (AF) quantum
critical point (QCP) are investigated by using the self-consistent
renormalization theory for SF and the strong coupling theory for SC. We
introduce a parameter y0 as a measure for the distance from the AFQCP which is
approximately proportional to (x-xc), x being the electron (e) or hole (h)
doping concentration to the half-filled band and xc being the value at the
AFQCP. We present phase diagrams in the T-y0 plane including contour maps of
the AF correlation length and AF and SC transition temperatures TN and Tc,
respectively. The Tc curve is dome-shaped with a maximum at around the AFQCP.
The calculated one-electron spectral density shows a pseudogap in the
high-density-of-states region near (pi,0) below around a certain temperature T*
and gives a contour map at the Fermi energy reminiscent of the Fermi arc. These
results are discussed in comparison with e- and h-doped high-Tc cuprates.Comment: 5 pages, 3 figure
Scaling of the magnetic response in doped antiferromagnets
A theory of the anomalous scaling of the dynamic magnetic response
in cuprates at low doping is presented. It is based on the memory function
representation of the dynamical spin suceptibility in a doped antiferromagnet
where the damping of the collective mode is constant and large, whereas the
equal-time spin correlations saturate at low . Exact diagonalization results
within the t-J model are shown to support assumptions. Consequences, both for
the scaling function and the normalization amplitude, are well in agreement
with neutron scattering results.Comment: 4 pages, 4 figure
Sub-kHz linewidth VECSEL for cold atoms experiments
We report sub-kHz linewidth operation of a frequency-stabilized, AlGaInP-based vertical-external-cavity surface-emitting laser (VECSEL) at 689nm, suitable for Strontium cold atom experiments. 170mW was emitted with linewidth ≤200Hz, determined via an optical beat note measurement
Spin fluctuations probed by NMR in paramagnetic spinel LiVO: a self-consistent renormalization theory
Low frequency spin fluctuation dynamics in paramagnetic spinel LiVO,
a rare 3-electron heavy fermion system, is investigated. A parametrized
self-consistent renormalization (SCR) theory of the dominant AFM spin
fluctuations is developed and applied to describe temperature and pressure
dependences of the low- nuclear spin-lattice relaxation rate in this
material. The experimental data for available down to K are
well reproduced by the SCR theory, showing the development of AFM spin
fluctuations as the paramagnetic metal approaches a magnetic instability under
the applied pressure. The low- upturn of detected below 0.6 K under
the highest applied pressure of 4.74 GPa is explained as the nuclear spin
relaxation effect due to the spin freezing of magnetic defects unavoidably
present in the measured sample of LiVO.Comment: 11 pages, 2 figure
Frequency-dependent spin susceptibility in the two-dimensional Hubbard model
A Quantum Monte Carlo calculation of dynamical spin susceptibility in the
half-filled 2D Hubbard model is presented for temperature and an
intermediate on-site repulsion . Using the singular value decomposition
technique we succeed in analytically continuing the Matsubara Green's function
into the real frequency domain and in deriving the spectral representation for
the longitudinal and transverse spin susceptibility. The simulation results,
while contradicting the random-phase approximation prediction of
antiferromagnetic long-range order at this temperature, are in agreement with
an extension of a self-consistent renormalization approach of Moriya. The
static susceptibility calculated using this technique is qualitatively
consistent with the simulation results.Comment: 4 pages, Revtex, encoded figs.uu file with 3 figures enclose
Ru-NMR Studies and Specific Heat Measurements of Bi3Ru3O11 and La4Ru6O19
Specific heats measurements and Ru-NMR studies have been carried out for
Bi3Ru3O11 and La4Ru6O19, which commonly have three-dimensional linkages of
edge-sharing pairs of RuO6 octahedra. The Knight shifts, the nuclear
spin-lattice relaxation rates 1/T1 and the electronic specific heats Cel of
these systems exhibit anomalous temperature (T) dependence at low temperatures,
as was pointed out by Khalifah et al. [Nature 411 (2001) 660.] for the latter
system based on their experimental data of the resistivity, magnetic
susceptibility and electronic specific heat. Ratios of 1/T1T to the square of
the spin component of the isotropic Knight shift, Kspin estimated for these
systems at low temperatures suggest that they have antiferromagnetic (AF) spin
fluctuations. It is confirmed by the fact that the T-dependences of 1/T1T and
Cel/T of the present systems can be explained by the self-consistent
renormalization theory for three dimensional itinerant electron systems with AF
spin fluctuations. All these results suggest that the AF fluctuations are the
primary origin of the characteristics of their low temperature physical
behavior.Comment: 9 pages, 8 figures, 2 Tables, submitted to J. Phys. Soc. Jp
Self-consistent renormalization theory of spin fluctuations in paramagnetic spinel LiV2O4
A phenomenological description for the dynamical spin susceptibility
observed in inelastic neutron scattering measurements
on powder samples of LiVO is developed in terms of the parametrized
self-consistent renormalization (SCR) theory of spin fluctuations. Compatible
with previous studies at , a peculiar distribution in -space
of strongly enhanced and slow spin fluctuations at 0.6
in LiVO is involved to derive the mode-mode coupling term
entering the basic equation of the SCR theory. The equation is solved
self-consistently with the parameter values found from a fit of theoretical
results to experimental data. For low temperatures, K, where the
SCR theory is more reliable, the observed temperature variations of the static
spin susceptibility and the relaxation rate at
are well reproduced by those suggested by the theory. For K, the present SCR is capable in predicting only main trends in
-dependences of and .
The discussion is focused on a marked evolution (from at towards low values at higher temperatures) of the dominant low-
integrated neutron scattering intensity .Comment: 7 pages, 1 figure. accepted to PR
Injection locking of a low cost high power laser diode at 461 nm
Stable laser sources at 461 nm are important for optical cooling of strontium
atoms. In most existing experiments this wavelength is obtained by frequency
doubling infrared lasers, since blue laser diodes either have low power or
large emission bandwidths. Here, we show that injecting less than 10 mW of
monomode laser radiation into a blue multimode 500 mW high power laser diode is
capable of slaving at least 50% of the power to the desired frequency. We
verify the emission bandwidth reduction by saturation spectroscopy on a
strontium gas cell and by direct beating of the slave with the master laser. We
also demonstrate that the laser can efficiently be used within the Zeeman
slower for optical cooling of a strontium atomic beam.Comment: 2nd corrected version (minor revisions); Manuscript accepted for
publication in Review of Scientific Instruments; 5 pages, 6 figure
Finite-temperature magnetism of FePd and CoPt alloys
The finite-temperature magnetic properties of FePd and
CoPt alloys have been investigated. It is shown that the
temperature-dependent magnetic behaviour of alloys, composed of originally
magnetic and non-magnetic elements, cannot be described properly unless the
coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through
the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is
included. A scheme for the calculation of the Curie temperature () for
this type of systems is presented which is based on the extended Heisenberg
Hamiltonian with the appropriate exchange parameters obtained from
{\em ab-initio} electronic structure calculations. Within the present study the
KKR Green's function method has been used to calculate the parameters.
A comparison of the obtained Curie temperatures for FePd and
CoPt alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure
- …