154 research outputs found
Bipolaronic blockade effect in quantum dots with negative charging energy
We investigate single-electron transport through quantum dots with negative
charging energy induced by a polaronic energy shift. For weak dot-lead tunnel
couplings, we demonstrate a bipolaronic blockade effect at low biases which
suppresses the oscillating linear conductance, while the conductance resonances
under large biases are enhanced. Novel conductance plateau develops when the
coupling asymmetry is introduced, with its height and width tuned by the
coupling strength and external magnetic field. It is further shown that the
amplitude ratio of magnetic-split conductance peaks changes from 3 to 1for
increasing coupling asymmetry. Though we demonstrate all these transport
phenomena in the low-order single-electron tunneling regime, they are already
strikingly different from the usual Coulomb blockade physics and are easy to
observe experimentally.Comment: 6 pages, 5 figure
Currents and current correlations in a topological superconducting nanowire beam splitter
A beam splitter consisting of two normal leads coupled to one end of a
topological superconducting nanowire via double quantum dot is investigated. In
this geometry, the linear current cross-correlations at zero temperature change
signs versus the overlap between the two Majorana bound states hosted by the
nanowire. Under symmetric bias voltages the net current flowing through the
nanowire is noiseless. These two features highlight the fermionic nature of
such exotic Majorana excitations though they are based on the
superconductivity. Moreover, there exists a unique local particle-hole symmetry
inherited from the self-Hermitian property of Majorana bound states, which is
apparently scarce in other systems. We show that such particular symmetry can
be revealed through measuring the currents under complementary bias voltages.Comment: 6 pages, 4 figure
Spin susceptibility of Anderson impurities in arbitrary conduction bands
Spin susceptibility of Anderson impurities is a key quantity in understanding
the physics of Kondo screening. Traditional numerical renormalization group
(NRG) calculation of the impurity contribution to
susceptibility, defined originally by Wilson in a flat wide band, has been
generalized before to structured conduction bands. The results brought about
non-Fermi-liquid and diamagnetic Kondo behaviors in , even
when the bands are not gapped at the Fermi energy. Here, we use the full
density-matrix (FDM) NRG to present high-quality data for the local
susceptibility and to compare them with
obtained by the traditional NRG. Our results indicate
that those exotic behaviors observed in are unphysical.
Instead, the low-energy excitations of the impurity in arbitrary bands only
without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We
also demonstrate that unlike the traditional NRG yielding
less accurate than , the FDM method allows a
high-precision dynamical calculation of at much reduced
computational cost, with an accuracy at least one order higher than
. Moreover, artifacts in the FDM algorithm to
, and origins of the spurious non-Fermi-liquid and
diamagnetic features are clarified. Our work provides an efficient
high-precision algorithm to calculate the spin susceptibility of impurity for
arbitrary structured bands, while negating the applicability of Wilson's
definition to such cases.Comment: the published versio
Engineering the Kondo and Fano effects in double quantum dots
We demonstrate delicate control over the Kondo effect and its interplay with
quantum interference in an Aharonov-Bohm interferometer containing one Kondo
dot and one noninteracting dot. It is shown that the Kondo resonance undergoes
a dramatic evolution as the interdot tunnel coupling progressively increases. A
novel triple Kondo splitting occurs from the interference between constant and
Lorentzian conduction bands that cooperate in forming the Kondo singlet. The
device also manifests a highly controllable Fano-Kondo effect in coherent
electronic transport, and can be tuned to a regime where the coupled dots
behave as decoupled dots.Comment: 5 pages, 4 figure
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