6,281 research outputs found
Dynamical properties of a nonequilibrium quantum dot close to localized-delocalized quantum phase transitions
We calculate the dynamical decoherence rate and susceptibility of a
nonequilibrium quantum dot close to the delocalized-to-localized quantum phase
transitions. The setup concerns a resonance-level coupled to two spinless
fermionic baths with a finite bias voltage and an Ohmic bosonic bath
representing the dissipative environment. The system is equivalent to an
anisotropic Kondo model.
As the dissipation strength increases, the system at zero temperature and
zero bias show quantum phase transition between a conducting delocalized phase
to an insulating localized phase. Within the nonequilibrium functional
Renormalization Group (FRG) approach, we address the finite bias crossover in
dynamical decoherence rate and charge susceptibility close to the phase
transition. We find the dynamical decoherence rate increases with increasing
frequency. In the delocalized phase, it shows a singularity at frequencies
equal to positive or negative bias voltage. As the system crossovers to the
localized phase, the decoherence rate at low frequencies get progressively
smaller and this sharp feature is gradually smeared out, leading to a single
linear frequency dependence. The dynamical charge susceptibility shows a
dip-to-peak crossover across the delocalized-to-localized transition. Relevance
of our results to the experiments is discussed.Comment: 7 pages, 7 figure
Statistics of spinons in the spin-liquid phase of Cs2CuCl4
Motivated by a recent experiment on Cs2CuCl4, we study the spin dynamics of
the spin-liquid phase of the spin-1/2 frustrated Heisenberg antiferromagnet on
the anisotropic triangular lattice. There have been two different proposals for
the spin-liquid phase of Cs2CuCl4. These spin-liquid states support different
statistics of spinons; the bosonic Sp(N) large-N mean field theory predicts
bosonic spinons while the SU(2) slave-boson mean field theory leads to
fermionic spinons. We compute the dynamical spin structure factor for both
types of spin-liquid state at zero and finite temperatures. While at zero
temperature both theories agree with experiment on a qualitative level, they
show substantial differences in the temperature dependence of the dynamical
spin structure factor.Comment: 4 pages, including 4 figure
Strange metal in paramagnetic heavy-fermion Kondo lattice: Dynamical large-N fermionic multi-channel approach
The mechanism of strange metal (SM) with unconventional charge transport near
magnetic phase transitions has become an outstanding open problem in correlated
electron systems. Recently, an exotic quantum critical SM phase was observed in
paramagnetic frustrated heavy-fermion materials near Kondo breakdown. We
establish a controlled theoretical framework to this issue via a dynamical
large-N fermionic multichannel approach to the two-dimensional Kondo-Heisenberg
lattice model, where KB transition separates a heavy-Fermi liquid from
fermionic spin-liquid state. With Kondo fluctuations being fully considered, we
find a distinct SM behavior with quasi-linear-in-temperature scattering rate
associated with KB. When particle-hole symmetry is present, signatures of a
critical spin-liquid SM phase as are revealed with
scaling extended to a wide range. We attribute these features to the interplay
of critical bosonic charge (Kondo) fluctuations and gapless fermionic spinons.
The implications of our results for the experiments are discussed.Comment: 6 pages, 4 figure
Tunneling between helical Majorana modes and helical Luttinger liquids
We propose and study the charge transport through single and double quantum
point contacts setup between helical Majorana modes and an interacting helical
Luttinger liquid. We show that the differential conductance decreases for
stronger repulsive interactions and that the point contacts become insulating
above a critical interaction strength. For a single point contact, the
differential conductance as a function of bias voltage shows a series of peaks
due to Andreev reflection of electrons in the Majorana modes. In the case of
two point contacts, interference phenomena make the structure of the individual
resonance peaks less universal and show modulations with different separation
distance between the contacts. For small separation distance the overall
features remain similar to the case of a single point contact.Comment: v.2: 14 pages, 11 figures; adding one figure, an appendix, and some
minor change
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