240 research outputs found
Zero-temperature Phase Diagram For Strongly-Correlated Nanochains
Recently there has been a resurgence of intense experimental and theoretical
interest on the Kondo physics of nanoscopic and mesoscopic systems due to the
possibility of making experiments in extremely small samples. We have carried
out exact diagonalization calculations to study the effect of the energy
spacing of the conduction band on the ground-state properties of a
dense Anderson model nanochain. The calculations reveal for the first time that
the energy spacing tunes the interplay between the Kondo and RKKY interactions,
giving rise to a zero-temperature versus hybridization phase diagram
with regions of prevailing Kondo or RKKY correlations, separated by a {\it free
spins} regime. This interplay may be relevant to experimental realizations of
small rings or quantum dots with tunable magnetic properties.Comment: 8 pages, 3 figures. J. Appl. Phys. (in press
Scalar potential effect in an integrable Kondo model
To study the impurity potential effect to the Kondo problem in a Luttinger
liquid, we propose an integrable model of two interacting half-chains coupled
with a single magnetic impurity ferromagnetically. It is shown that the scalar
potential effectively reconciles the spin dynamics at low temperatures.
Generally, there is a competition between the Kondo coupling and the
impurity potential . When the ferromagnetic Kondo coupling dominates over
the impurity potential (), the Furusaki-Nagaosa many-body singlet can
be perfectly realized. However, when the impurity potential dominates over the
Kondo coupling (), the fixed point predicted by Furusaki and
Nagaosa is unstable and the system must flow to a weak coupling fixed point. It
is also found that the effective moment of the impurity measured from the
susceptibility is considerably enlarged by the impurity potential. In addition,
some quantum phase transitions driven by the impurity potential are found and
the anomaly residual entropy is discussed.Comment: volume enlarged, some new references are adde
Magnetoresistance in the s-d Model with Arbitrary Impurity Spin
The magnetoresistance, the number of the localized electrons, and the s-wave
scattering phase shift at the Fermi level for the s-d model with arbitrary
impurity spin are obtained in the ground state. To obtain above results some
known exact results of the Bethe ansatz method are used. As the impurity spin S
= 1/2, our results coincide with those obtained by Ishii \textit{et al%}. The
compairsion between the theoretical and experimental magneticresistence for
impurity S = 1/2 is re-examined.Comment: 6 pages, 2 figure
Intersite coupling effects in a Kondo lattice
The La dilution of the Kondo lattice CeCoIn_5 is studied. The scaling laws
found for the magnetic susceptibility and the specific heat reveal two
well-separated energy scales, corresponding to the single impurity Kondo
temperature T_K and an intersite spin-liquid temperature T^*. The Ce-dilute
alloy has the expected Fermi liquid ground state, while the specific heat and
resistivity in the dense Kondo regime exhibit non-Fermi-liquid behavior, which
scales with T^*. These observations indicate that the screening of the magnetic
moments in the lattice involves antiferromagnetic intersite correlations with a
larger energy scale in comparison with the Kondo impurity case.Comment: 4 pages, 4 figure
Exactly solvable toy models of unconventional magnetic alloys: Bethe Ansatz versus Renormalization Group method
We propose toy models of unconventional magnetic alloys, in which the density
of band states, , and hybridization, , are energy
dependent; it is assumed, however, that
, and hence an effective
electron-impurity coupling is
energy independent. In the renormalization group approach, the physics of the
system is assumed to be governed by only rather than by
separate forms of and . However, an exact Bethe
Ansatz solution of the toy Anderson model demonstrates a crucial role of a form
of inverse band dispersion .Comment: A final version. A previous one has been sent to Archive because of
my technical mistake. Sorr
Ghost spins and novel quantum critical behavior in a spin chain with local bond-deformation
We study the boundary impurity-induced critical behavior in an integrable
SU(2)-invariant model consisting of an open Heisenberg chain of arbitrary
spin- (Takhatajian-Babujian model) interacting with an impurity of spin
located at one of the boundaries. For or , the
impurity interaction has a very simple form which
describes the deformed boundary bond between the impurity and the
first bulk spin with an arbitrary strength . With a weak
coupling , the impurity is completely compensated,
undercompensated, and overcompensated for , and as in the
usual Kondo problem. While for strong coupling , the
impurity spin is split into two ghost spins. Their cooperative effect leads to
a variety of new critical behaviors with different values of .Comment: 16 pages revtex, no figur
Exact Thermodynamics of Disordered Impurities in Quantum Spin Chains
Exact results for the thermodynamic properties of ensembles of magnetic
impurities with randomly distributed host-impurity couplings in the quantum
antiferromagnetic Heisenberg model are presented. Exact calculations are done
for arbitrary values of temperature and external magnetic field. We have shown
that for strong disorder the quenching of the impurity moments is absent. For
weak disorder the screening persists, but with the critical non-Fermi-liquid
behaviors of the magnetic susceptibility and specific heat. A comparison with
the disordered Kondo effect experiments in dirty metallic alloys is performed.Comment: 4 pages Late
Open su(4)-invariant spin ladder with boundary defects
The integrable su(4)-invariant spin-ladder model with boundary defect is
studied using the Bethe ansatz method. The exact phase diagram for the ground
state is given and the boundary quantum critical behavior is discussed. It
consists of a gapped phase in which the rungs of the ladder form singlet states
and a gapless Luttinger liquid phase. It is found that in the gapped phase the
boundary bound state corresponds to an unscreened local moment, while in the
Luttinger liquid phase the local moment is screened at low temperatures in
analogy to the Kondo effect.Comment: Revtex 9 pages, published in PR
Integrable model of interacting XX and Fateev-Zamolodchikov chains
We consider the exact solution of a model of correlated particles, which is
presented as a system of interacting XX and Fateev-Zamolodchikov chains. This
model can also be considered as a generalization of the multiband anisotropic
model in the case we restrict the site occupations to at most two
electrons. The exact solution is obtained for the eigenvalues and eigenvectors
using the Bethe-ansatz method.Comment: 10 pages, no figure
Fermi Surface of Alpha-Uranium at Ambient Pressure
We have performed de Haas-van Alphen measurements of the Fermi surface of
alpha-uranium single crystals at ambient pressure within the alpha-3 charge
density wave (CDW) state from 0.020 K - 10 K and magnetic fields to 35 T using
torque magnetometry. The angular dependence of the resulting frequencies is
described. Effective masses were measured and the Dingle temperature was
determined to be 0.74 K +/- 0.04 K. The observation of quantum oscillations
within the alpha-3 CDW state gives new insight into the effect of the charge
density waves on the Fermi surface. In addition we observed no signature of
superconductivity in either transport or magnetization down to 0.020 K
indicating the possibility of a pressure-induced quantum critical point that
separates the superconducting dome from the normal CDW phase.Comment: 11 pages, 4 figures, 3 table
- …