3,708 research outputs found
A factorization of a super-conformal map
A super-conformal map and a minimal surface are factored into a product of
two maps by modeling the Euclidean four-space and the complex Euclidean plane
on the set of all quaternions. One of these two maps is a holomorphic map or a
meromorphic map. These conformal maps adopt properties of a holomorphic
function or a meromorphic function. Analogs of the Liouville theorem, the
Schwarz lemma, the Schwarz-Pick theorem, the Weierstrass factorization theorem,
the Abel-Jacobi theorem, and a relation between zeros of a minimal surface and
branch points of a super-conformal map are obtained.Comment: 21 page
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
Fermi surface and antiferromagnetism in the Kondo lattice: an asymptotically exact solution in d>1 Dimensions
Interest in the heavy fermion metals has motivated us to examine the quantum
phases and their Fermi surfaces within the Kondo lattice model. We demonstrate
that the model is soluble asymptotically exactly in any dimension d>1, when the
Kondo coupling is small compared with the RKKY interaction and in the presence
of antiferromagnetic ordering. We show that the Kondo coupling is exactly
marginal in the renormalization group sense, establishing the stability of an
ordered phase with a small Fermi surface, AFs. Our results have implications
for the global phase diagram of the heavy fermion metals, suggesting a Lifshitz
transition inside the antiferromagnetic region and providing a new perspective
for a Kondo-destroying antiferromagnetic quantum critical point.Comment: 4 pages, 4 figures; (v2) corrected typos and added
reference/acknowledgment; (v3) version as published in Physical Review
Letters (July, 2007
Anisotropy, Itineracy, and Magnetic Frustration in High-Tc Iron Pnictides
Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest () and next-nearest () exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.Comment: Fig.4 updated: Phys. Rev. Lett (in press
Analysis of Superconductivity in d-p Model on Basis of Perturbation Theory
We investigate the mass enhancement factor and the superconducting transition
temperature in the d-p model for the high-\Tc cuprates. We solve the
\'Eliashberg equation using the third-order perturbation theory with respect to
the on-site Coulomb repulsion . We find that when the energy difference
between d-level and p-level is large, the mass enhancement factor becomes large
and \Tc tends to be suppressed owing to the difference of the density of
state for d-electron at the Fermi level. From another view point, when the
energy difference is large, the d-hole number approaches to unity and the
electron correlation becomes strong and enhances the effective mass. This
behavior for the electron number is the same as that of the f-electron number
in the heavy fermion systems. The mass enhancement factor plays an essential
role in understanding the difference of \Tc between the LSCO and YBCO
systems.Comment: 4pages, 9figures, to be published in J. Phys. Soc. Jp
Field-induced paramagnons at the metamagnetic transition in Ca1.8Sr0.2RuO4
The magnetic excitations in Ca1.8Sr0.2RuO4 were studied across the
metamagnetic transition and as a function of temperature using inelastic
neutron scattering. At low temperature and low magnetic field the magnetic
response is dominated by a complex superposition of incommensurate
antiferromagnetic fluctuations. Upon increasing the magnetic field across the
metamagnetic ransition, paramagnon and finally well-defined magnon scattering
is induced, partially suppressing the incommensurate signals. The high-field
phase in Ca1.8Sr0.2RuO4 has, therefore, to be considered as an intrinsically
ferromagnetic state stabilized by the magnetic field
Coexistence of Superconductivity and Antiferromagnetism in Heavy-Fermion Superconductor CeCu_{2}(Si_{1-x}Ge_{x})_{2} Probed by Cu-NQR --A Test Case for the SO(5) Theory--
We report on the basis of Cu-NQR measurements that superconductivity (SC) and
antiferromagnetism (AF) coexist on a microscopic level in
CeCu_{2}(Si_{1-x}Ge_{x})_{2}, once a tiny amount of 1%Ge (x = 0.01) is
substituted for Si. This coexistence arises because Ge substitution expands the
unit-cell volume in nearly homogeneous CeCu2Si2 where the SC coexists with
slowly fluctuating magnetic waves. We propose that the underlying exotic phases
of SC and AF in either nearly homogeneous or slightly Ge substituted CeCu2Si2
are accountable based on the SO(5) theory that unifies the SC and AF. We
suggest that the mechanism of the SC and AF is common in CeCu2Si2.Comment: 7 pages with 6 figures embedded in the text. To be published in J.
Phys. Condens. Matter, 200
Novel critical exponent of magnetization curves near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3 (A = Ca, La0.5Na0.5, and La)
We report a novel critical exponent delta=3/2 of magnetization curves
M=H^{1/delta} near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3
(A = Ca, La0.5Na0.5, and La), which the mean field theory of the
Ginzburg-Landau-Wilson type fails to reproduce. The effect of dirty
ferromagnetic spin fluctuations might be a key.Comment: 4 pages, 5 figure
Correlated band theory of spin and orbital contributions to Dzyaloshinskii-Moriya interactions
A new approach for calculations of Dzyaloshinskii-Moriya interactions in
molecules and crystals is proposed. It is based on the exact perturbation
expansion of total energy of weak ferromagnets in the canting angle with the
only assumption of local Hubbard-type interactions. This scheme leads to a
simple and transparent analytical expression for Dzyaloshinskii-Moriya vector
with a natural separation into spin and orbital contributions. The main problem
was transferred to calculations of effective tight-binding parameters in the
properly chosen basis including spin-orbit coupling. Test calculations for
LaCuO give the value of canting angle in a good agreement with
experimental data.Comment: 4 pages, 1 figur
Metamagnetic Quantum Criticality Revealed by 17O-NMR in the Itinerant Metamagnet Sr3Ru2O7
We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7
as a function of magnetic field and temperature using 17O-NMR. This system sits
close to a metamagnetic quantum critical point (MMQCP) for the field
perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior
at low temperatures except for a narrow field region close to the MMQCP. The
nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced
on approaching the metamagnetic critical field of 7.9 T and at the critical
field 1/T1T continues to increase and does not show Fermi- liquid behavior down
to 0.3 K. The temperature dependence of T1T in this region suggests the
critical temperature Theta to be 0 K, which is a strong evidence that the spin
dynamics possesses a quantum critical character. Comparison between uniform
susceptibility and 1/T1T reveals that antiferromagnetic fluctuations instead of
two-dimensional ferromagnetic fluctuations dominate the spin fluctuation
spectrum at the critical field, which is unexpected for itinerant
metamagnetism.Comment: 5 pages, 4 figures, Accepted by Phys. Rev. Let
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