173 research outputs found

### Kondo Physics and Exact Solvability of Double Dots Systems

We study two double dot systems, one with dots in parallel and one with dots
in series, and argue they admit an exact solution via the Bethe ansatz. In the
case of parallel dots we exploit the exact solution to extract the behavior of
the linear response conductance. The linear response conductance of the
parallel dot system possesses multiple Kondo effects, including a Kondo effect
enhanced by a nonpertubative antiferromagnetic RKKY interaction, has
conductance zeros in the mixed valence regime, and obeys a non-trivial form of
the Friedel sum rule.Comment: 4 pages, 2 figures; v2: published form to appear in August 2007 issue
of Phys. Rev. Let

### Orbital Dependence of Quasiparticle Lifetimes in Sr2RuO4

Using a phenomenological Hamiltonian, we investigate the quasiparticle
lifetimes and dispersions in the three low energy bands, gamma, beta, and alpha
of Sr2RuO4. Couplings in the Hamiltonian are fixed so as to produce the mass
renormalization as measured in magneto-oscillation experiments. We thus find
reasonable agreement in all bands between our computed lifetimes and those
measured in ARPES experiments by Kidd et al. [1] and Ingle et al. [2]. In
comparing computed to measured quasiparticle dispersions, we however find good
agreement in the alpha-band alone.Comment: 7 pages, 5 figure

### Understanding the entanglement entropy and spectra of 2D quantum systems through arrays of coupled 1D chains

We describe an algorithm for studying the entanglement entropy and spectrum
of 2D systems, as a coupled array of $N$ one dimensional chains in their
continuum limit. Using the algorithm to study the quantum Ising model in 2D,
(both in its disordered phase and near criticality) we confirm the existence of
an area law for the entanglement entropy and show that near criticality there
is an additive piece scaling as $c_{eff}\log (N)/6$ with $c_{eff} \approx 1$.
\textcolor{black}{Studying the entanglement spectrum, we show that entanglement
gap scaling can be used to detect the critical point of the 2D model. When
short range (area law) entanglement dominates we find (numerically and
perturbatively) that this spectrum reflects the energy spectrum of a single
quantum Ising chain.Comment: 8 pages (4 + supplementary material). 10 figure

### Glimmers of a Quantum KAM Theorem: Insights from Quantum Quenches in One Dimensional Bose Gases

Real-time dynamics in a quantum many-body system are inherently complicated
and hence difficult to predict. There are, however, a special set of systems
where these dynamics are theoretically tractable: integrable models. Such
models possess non-trivial conserved quantities beyond energy and momentum.
These quantities are believed to control dynamics and thermalization in low
dimensional atomic gases as well as in quantum spin chains. But what happens
when the special symmetries leading to the existence of the extra conserved
quantities are broken? Is there any memory of the quantities if the breaking is
weak? Here, in the presence of weak integrability breaking, we show that it is
possible to construct residual quasi-conserved quantities, so providing a
quantum analog to the KAM theorem and its attendant Nekhoreshev estimates. We
demonstrate this construction explicitly in the context of quantum quenches in
one-dimensional Bose gases and argue that these quasi-conserved quantities can
be probed experimentally.Comment: 21 pages with appendices; 13 figures; version accepted by PR

### Studying the Perturbed Wess-Zumino-Novikov-Witten SU(2)k Theory Using the Truncated Conformal Spectrum Approach

We study the $SU(2)_k$ Wess-Zumino-Novikov-Witten (WZNW) theory perturbed by
the trace of the primary field in the adjoint representation, a theory
governing the low-energy behaviour of a class of strongly correlated electronic
systems. While the model is non-integrable, its dynamics can be investigated
using the numerical technique of the truncated conformal spectrum approach
combined with numerical and analytical renormalization groups (TCSA+RG). The
numerical results so obtained provide support for a semiclassical analysis
valid at $k\gg 1$. Namely, we find that the low energy behavior is sensitive to
the sign of the coupling constant, $\lambda$. Moreover for $\lambda>0$ this
behavior depends on whether $k$ is even or odd. With $k$ even, we find
definitive evidence that the model at low energies is equivalent to the massive
$O(3)$ sigma model. For $k$ odd, the numerical evidence is more equivocal, but
we find indications that the low energy effective theory is critical.Comment: 30 pages, 19 eps figures, LaTeX2e file. Version 2: manuscript
accepted for publication; small changes in text and in one of the figure

### Interference effects in interacting quantum dots

In this paper we study the interplay between interference effects in quantum
dots (manifested through the appearance of Fano resonances in the conductance),
and interactions taken into account in the self-consistent Hartree-Fock
approximation. In the non-interacting case we find that interference may lead
to the observation of more than one conductance peak per dot level as a
function of an applied gate voltage. This may explain recent experimental
findings, which were thought to be caused by interaction effects. For the
interacting case we find a wide variety of different interesting phenomena.
These include both monotonous and non-monotonous filling of the dot levels as a
function of an applied gate voltage, which may occur continuously or even
discontinuously. In many cases a combination of the different effects can occur
in the same sample. The behavior of the population influences, in turn, the
conductance lineshape, causing broadening and asymmetry of narrow peaks, and
determining whether there will be a zero transmission point. We elucidate the
essential role of the interference between the dot levels in determining these
outcomes. The effects of finite temperatures on the results are also examined.Comment: 11 pages, 9 fugures, REVTeX

### Magnetic Response in the Underdoped Cuprates

We examine the dynamical magnetic response of the underdoped cuprates by
employing a phenomenological theory of a doped resonant valence bond state
where the Fermi surface is truncated into four pockets. This theory predicts a
resonant spin response which with increasing energy (0 to 100meV) appears as an
hourglass. The very low energy spin response is found at (pi,pi +- delta) and
(pi +- delta,pi) and is determined by scattering from the pockets' frontside to
the tips of opposite pockets where a van Hove singularity resides. At energies
beyond 100 meV, strong scattering is seen from (pi,0) to (pi,pi). This theory
thus provides a semi-quantitative description of the spin response seen in both
INS and RIXS experiments at all relevant energy scales

### Superconductivity generated by coupling to a Cooperon in a 2-dimensional array of 4-leg Hubbard ladders

Starting from an array of four-leg Hubbard ladders weakly doped away from
half-filling and weakly coupled by inter-ladder tunneling, we derive an
effective low energy model which contains a partially truncated Fermi surface
and a well defined Cooperon excitation formed by a bound pair of holes. An
attractive interaction in the Cooper channel is generated on the Fermi surface
through virtual scattering into the Cooperon state. Although the model is
derived in the weak coupling limit of a four-leg ladder array, an examination
of exact results on finite clusters for the strong coupling t-J model suggests
the essential features are also present for a strong coupling Hubbard model on
a square lattice near half-filling.Comment: 20 pages, 4 figure

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