259 research outputs found
The 2-Channel Kondo Model II: CFT Calculation of Non-Equilibrium Conductance through a Nanoconstriction containing 2-Channel Kondo Impurities
Recent experiments by Ralph and Buhrman on zero-bias anomalies in quenched Cu
nanoconstrictions (reviewed in the preceding paper, I), are in accord with the
assumption that the interaction between electrons and nearly degenerate
two-level systems in the constriction can be described, for sufficiently small
voltages and temperatures (V,T < \Tk), by the 2-channel Kondo (2CK) model.
Motivated by these experiments, we introduce a generalization of the 2CK model,
which we call the nanoconstriction 2-channel Kondo model (NTKM), that takes
into account the complications arising from the non-equilibrium electron
distribution in the nanoconstriction. We calculate the conductance of
the constriction in the weakly non-equilibrium regime of V,T \ll \Tk by
combining concepts from Hershfield's -operator formulation of
non-equilibrium problems and Affleck and Ludwig's exact conformal field theory
(CFT) solution of the 2CK problem (CFT technicalities are discussed in a
subsequent paper, III). Finally, we extract from the conductance a universal
scaling curve and compare it with experiment. Combining our results
with those of Hettler, Kroha and Hershfield, we conclude that the NTKM achieves
quantitative agreement with the experimental scaling data.Comment: Final published version (minor revisions only), 41 pages RevTeX, 9
encapsulated postscript figure
Confinement induced interlayer molecules: a route to strong interatomic interactions
We study theoretically the interaction between two species of ultracold atoms
confined into two layers of a finite separation, and demonstrate the existence
of new types of confinement-induced interlayer bound and quasi-bound molecules:
these novel exciton-like interlayer molecules appear for both positive and
negative scattering lengths, and exist even for layer separations many times
larger than the interspecies scattering length. The lifetime of the quasi-bound
molecules grows exponentially with increasing layer separation, and they can
therefore be observed in simple shaking experiments, as we demonstrate through
detailed many-body calculations. These quasi-bound molecules can also give rise
to novel interspecies Feshbach resonances, enabling one to control
geometrically the interaction between the two species by changing the layer
separation. Rather counter-intuitively, the species can be made strongly
interacting, by increasing their spatial separation. The separation induced
interlayer resonances provide a powerful tool for the experimental control of
interspecies interactions and enables one to realize novel quantum phases of
multicomponent quantum gases.Comment: 13 pages, 9 figure
Floquet topological phases coupled to environments and the induced photocurrent
We consider the fate of a helical edge state of a spin Hall insulator and its
topological transition in presence of a circularly polarized light when coupled
to various forms of environments. A Lindblad type equation is developed to
determine the fermion occupation of the Floquet bands. We find by using
analytical and numerical methods that non-secular terms, corresponding to
2-photon transitions, lead to a mixing of the band occupations, hence the light
induced photocurrent is in general not perfectly quantized in the presence of
finite coupling to the environment, although deviations are small in the
adiabatic limit. Sharp crossovers are identified at frequencies and
( is the strength of light-matter coupling) with
the former resembling to a phase transition.Comment: 7+4 pages, 6+2 figure
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