8,815 research outputs found
Spin Tunneling, Berry phases and Doped Antiferromagnets
Interference effects between Berry phase factors in spin tunneling systems
have been discussed in recent Letters by Loss, DiVincenzo and Grinstein and von
Delft and Henley. This Comment points out that Berry phases in spin tunneling
are important in another interesting case: the two dimensional doped
antiferromagnet. I show that the dispersion of a single hole in the t-J model
changes sign as where is the size of the spins. This provides
an interpretation of the numerical results for the s=\half model, and a
prediction for other spin sizes.Comment: 5 pages, LaTe
Critical Entropy of Quantum Heisenberg Magnets on Simple-Cubic Lattices
We analyze the temperature dependence of the entropy of the spin-1/2
Heisenberg model on the three-dimensional simple-cubic lattice, for both the
case of antiferromagnetic and ferromagnetic nearest neighbor exchange
interactions. Using optimized extended ensemble quantum Monte Carlo
simulations, we extract the entropy at the critical temperature for magnetic
order from a finite-size scaling analysis. For the antiferromagnetic case, the
critical entropy density equals 0.341(5), whereas for the ferromagnet, a
larger value of 0.401(5) is obtained. We compare our simulation results
to estimates put forward recently in studies assessing means of realizing the
antiferromagnetic N\'eel state in ultra-cold fermion gases in optical lattices.Comment: 3 pages, 2 figures; published versio
Coulomb corrections to superallowed beta decay in nuclei
Corrections to the superallowed beta decay matrix elements are evaluated in
perturbation theory using the notion of the isovector monopole resonance. The
calculation avoids the separation into different contributions and thus
presents a consistent, systematic and more transparent approach. Explicit
expressions for the Coulomb correction as a function of mass number A, are
given.Comment: 10 page
Nature of an intermediate non-Fermi liquid state in Ge-substituted YbRhSi: Fermionized skyrmions, Lifshitz transition, Skyrmion liquid, and Gruneisen ratio
We propose a skyrmion liquid state for the non-Fermi liquid (NFL) phase in
Ge-substituted YbRhSi, where skyrmions form their Fermi surface,
argued to result from the strongly coupled nature between skyrmions and
itinerant electrons. The fermionized skyrmion theory identifies the
antiferromagnetic (AF) transition with the Lifshitz transition, where the
quantum critical point (QCP) is characterized by the dynamical critical
exponent . Nonlocal interactions between skyrmions allow a critical line
above the AF QCP, which originates from the Kondo-coupling effect with
itinerant electrons. This critical line is described by the skyrmion liquid
state, which results in Landau damping for spin fluctuations, thus
characterized by . As a result, the Gruneisen ratio is predicted to
change from at the AF QCP to in the NFL phase
Electric charging of magnetic textures on the surface of a topological insulator
A three-dimensional topological insulator manifests gapless surface modes,
described by two-dimensional Dirac equation. We study magnetic textures, such
as domain walls and vortices, in a ferromagnetic thin film deposited on a
three-dimensional topological insulator. It is shown that these textures can be
electrically charged, ascribed to the proximity effect with the Dirac surface
states. We derive a general relation between the electric and the magnetic
charges. As a physical consequence, we discuss domain wall motion driven by an
applied electric field, which promises magnetic devices with high thermal
efficiency.Comment: 5 pages, 2 figure
"Super-radiance" and the width of exotic baryons
It is suggested that the narrow width of the recently observed resonance
with strangeness could be a result of the
super-radiance mechanism of the redistribution of the widths of overlapping
resonances due to their coupling through common decay channels.Comment: This is an update of the original version submitted on October 08,
2003; it includes consideration of an additional model and one new figur
Spin Chains with Periodic Array of Impurities
We investigate the spin chain model composed of periodic array of two kinds
of spins and , which allows us to study the spin chains with
impurities as well as the alternating spin chains in a unified fashion. By
using the Lieb-Shultz-Mattis theorem, we first study the model rigorously, and
then by mapping it to the non-linear sigma model, we extensively investigate
low-energy properties with particular emphasis on the competition between the
massive and massless phases.Comment: 5 pages, revtex, To appear in PR
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