97 research outputs found
Composite Spin-Triplet Superconductivity in an Symmetric Lattice Model
The two-channel Anderson lattice model which has
symmetry is of relevance to understanding of the magnetic, quadrupolar and
superconducting phases in UThBe or Pr base skutterudite
compounds such as PrFeP or PrOsSb. Possible
unconventional superconducting phases of the model are explored. They are
characterized by a composite order parameter comprising of a local magnetic or
quadrupolar moment and a triplet conduction electron Cooper-pair. This binding
of local degrees of freedom removes the entropy of the non Fermi-liquid normal
state. We find superconducting transitions in the intermediate valence regime
which are suppressed in the stable moment regime. The gap function is non
analytic and odd in frequency: a pseudo-gap develops in the conduction electron
density of states which vanishes as close to . In the
strong intermediate valent regime, the gap function acquires an additional
\k-dependence.Comment: 20 pages, 12 figures, latex EPJ format. Accepted for publication as
Eur.Phys.J.
Comment on "Scaling feature of magnetic field induced Kondo-peak splittings"
In a recent work Zhang and coworkers (PRB 82, 075111 (2010)) studied the
Zeeman splitting of the Kondo resonance for the single impurity Anderson model
in a finite magnetic field with the numerical renormalization group (NRG)
method. There, it was found that with increasing magnetic field the
position of the Kondo resonance in the total spectral function \textit{does
not} approach its position in the spin resolved spectral function.
Additionally, the position of the Kondo maximum exceeded the Zeeman energy for
, where is the low energy Kondo scale of the model
(, ). In this comment we argue that both these findings
are produced by an improper choice of NRG parameter values. However, we
reproduce the crossover in the splitting from Kondo-like behavior to a
non-universal splitting larger than the Zeeman energy, but this crossover
occurs at much larger fields of the order of the charge scale.Comment: Minor revisions; same version as publishe
On steady-state currents through nano-devices: a scattering-states numerical renormalization group approach to open quantum systems
We propose a numerical renormalization group (NRG) approach to steady-state
currents through nano-devices. A discretization of the scattering-states
continuum ensures the correct boundary condition for an open quantum system. We
introduce two degenerate Wilson chains for current carrying left and
right-moving electrons reflecting time-reversal symmetry in the absence of a
finite bias . We employ the time-dependent NRG to evolve the known
steady-state density operator for a non-interacting junction into the density
operator of the fully interacting nano-device at finite bias. We calculate the
temperature dependent current as function of and applied external magnetic
field using a recently developed algorithm for non-equilibrium spectral
functions.Comment: 4 pages, 6 figure
Equilibrium and non-equilibrium dynamics of the sub-ohmic spin-boson model
Employing the non-perturbative numerical renormalization group method, we
study the dynamics of the spin-boson model, which describes a two-level system
coupled to a bosonic bath with spectral density J(omega) propto omega^s. We
show that, in contrast to the case of ohmic damping, the delocalized phase of
the sub-ohmic model cannot be characterized by a single energy scale only, due
to the presence of a non-trivial quantum phase transition. In the strongly
sub-ohmic regime, s<<1, weakly damped coherent oscillations on short time
scales are possible even in the localized phase - this is of crucial relevance,
e.g., for qubits subject to electromagnetic noise.Comment: 4 pages, 6 figures; final version, as publishe
- …