18 research outputs found
Kondo tunneling through real and artificial molecules
When a cerocene molecule is chemisorbed on metallic substrate, or when an
asymmetric double dot is hybridized with itinerant electrons, its singlet
ground state crosses its lowly excited triplet state, leading to a competition
between the Zhang-Rice mechanism of singlet-triplet splitting in a confined
cluster and the Kondo effect (which accompanies the tunneling through quantum
dot under a Coulomb blockade restriction). The rich physics of an underscreened
S=1 Kondo impurity in the presence of low-lying triplet/singlet excitations is
exposed. Estimates of the magnetic susceptibility and the electric conductance
are presented.Comment: 4 two-column revtex pages including 1 eps figur
Solution of the two impurity, two channel Kondo Model
We solve the two-impurity two-channel Kondo model using a combination of
conformal invariance and bosonisation techniques. The odd-even symmetric case
is analysed in detail. The RKKY interaction turns out to be exactly marginal,
resulting in a line of non-Fermi liquid fixed points. Explicit formulae are
given for the critical exponents and for the finite-size spectrum, which depend
continuously on a single parameter. The marginal line spans a range of values
of the RKKY coupling which goes from the infinitely strong ferromagnetic
point (associated with a 4-channel spin-1 Kondo model) to a finite
antiferromagnetic critical value beyond which a Fermi liquid is
recovered. We also find that, when the odd-even symmetry is broken, the
marginal line is unstable for ferromagnetic , while for antiferromagnetic
it extends into a manifold of fixed points.Comment: 9 pages, preprint LPTENS 94/1
The Excitation Spectrum of a Bose-Einstein Condensate
We report the first measurement of the excitation spectrum and the static
structure factor of a Bose-Einstein condensate. The excitation spectrum
displays a linear phonon regime, as well as a parabolic single-particle regime.
The linear regime provides an upper limit for the superfluid critical velocity,
by the Landau criterion. The excitation spectrum agrees well with the
Bogoliubov spectrum, in the local density approximation. This agreement
continues even for excitations close to the long-wavelength limit of the region
of applicability of the approximation. Feynman's relation between the
excitation spectrum and the static structure factor is verified, within an
overall constant
\eta-superconductivity in the Hubbard chain with pair hopping
The ground state phase diagram of the 1D Hubbard chain with pair-hopping
interaction is studied. The analysis of the model is performed using the
continuum-limit field theory approach and exact diagonalization studies. At
half-filling the phase diagram is shown to consist of two superconducting
states with Cooper pair center-of-mass momentum Q=0 (BCS-\eta_0 phase) and
Q=\pi (\eta_\pi-phase) and four insulating phases corresponding to the Mott
antiferromagnet, the Peierls dimerized phase, the charge-density-wave (CDW)
insulator as well as an unconventional insulating phase characterized by the
coexistence of a CDW and a bond-located staggered magnetization. Away from
half-filling the phase diagram consists of the superconducting BCS-\eta_0 and
\eta_\pi phases and the metallic Luttinger-liquid phase. The BCS-\eta_0 phase
exhibits smooth crossover from a weak-coupling BCS type to a strong coupling
local-pair regime. The \eta_\pi phase shows properties of the doublon (zero
size Cooper pair) superconductor with Cooper pair center-of-mass momentum
Q=\pi. The transition into the \eta_\pi- paired state corresponds to an abrupt
change in the groundstate structure. After the transition the conduction band
is completely destroyed and a new \eta_\pi-pair band corresponding to the
strongly correlated doublon motion is created.Comment: 15 pages Revtex, 15 embedded eps figure
Quantum liquids resulting from quark systems with four-quark interaction
Quark ensembles influenced by strong stochastic vacuum gluon fields are investigated within the four-fermion interaction approximation. The comparative analysis of several quantum liquid models is performed and this analysis leads to the conclusion that the presence of a gas–liquid phase transition is their characteristic feature. The problem of the instability of small quark number droplets is discussed and it is argued that it is rooted in the chiral soliton formation. The existence of a mixed phase of the vacuum and baryon matter is proposed as a possible explanation of the latter stability
On the Emery-Kivelson Solution of the two channel Kondo problem
We consider the two channel Kondo model in the Emery-Kivelson approach, and
calculate the total susceptibility enhancement due to the impurity
. We find that exactly vanishes at
the solvable point, in a completely analogous way to the singular part of the
specific heat . A perturbative calculation around the solvable point
yields the generic behaviour , and the known universal value of the Wilson ratio .
From this calculation, the Kondo temperature can be identified and is found to
behave as the inverse-square of the perturbation parameter. The small field,
zero-temperature behaviour is also recovered.Comment: 7 pages, REVTEX, 1 figure available on request, LPTENS preprint 93/4