450 research outputs found
Dynamics of doublon-holon pairs in Hubbard two-leg ladders
The dynamics of holon-doublon pairs is studied in Hubbard two-leg ladders
using the time-dependent Density Matrix Renormalization Group method. We find
that the geometry of the two-leg ladder, that is qualitatively different from a
one-dimensional chain due to the presence of a spin-gap, strongly affects the
propagation of a doublon-holon pair. Two distinct regimes are identified. For
weak inter-leg coupling, the results are qualitatively similar to the case of
the propagation previously reported in Hubbard chains, with only a
renormalization of parameters. More interesting is the case of strong inter-leg
coupling where substantial differences arise, particularly regarding the double
occupancy and properties of the excitations such as the doublon speed. Our
results suggest a connection between the presence of a spin gap and qualitative
changes in the doublon speed, indicating a weak coupling between the doublon to
magnetic excitations.Comment: 8 pages, 9 figures. Published versio
Transport signatures of Kondo physics and quantum criticality in graphene with magnetic impurities
Localized magnetic moments have been predicted to develop in graphene samples
with vacancies or adsorbates. The interplay between such magnetic impurities
and graphene's Dirac quasiparticles leads to remarkable many-body phenomena,
which have so far proved elusive to experimental efforts. In this article, we
study the thermodynamic, spectral and transport signatures of quantum
criticality and Kondo physics of a dilute ensemble of atomic impurities in
graphene. We consider vacancies and adatoms that either break or preserve
graphene's and inversion symmetries. In a neutral graphene sample, all
cases display symmetry-dependent quantum criticality, leading to enhanced
impurity scattering for asymmetric impurities, in a manner analogous to
bound-state formation by nonmagnetic resonant scatterers. Kondo correlations
emerge only in the presence of a back gate, with estimated Kondo temperatures
well within the experimentally accessible domain for all impurity types. For
symmetry-breaking impurities at charge neutrality, quantum criticality is
signaled by resistivity scaling, leading to full insulating behavior
at low temperatures, while low-temperature resistivity plateaus appear both in
the non-critical and Kondo regimes. By contrast, the resitivity contribution
from symmetric vacancies and hollow-site adsorbates vanishes at charge
neutrality and for arbitrary back gate voltages, respectively. This implies
that local probing methods are required for the detection of both Kondo and
quantum critical signatures in these symmetry-preserving cases.Comment: Final published version, with corrected figures, improved notation,
and added references. 12 pages, including 8 figures and one appendi
Tunable pseudogap Kondo effect and quantum phase transitions in Aharonov-Bohm interferometers
We study two quantum dots embedded in the arms of an Aharonov-Bohm ring
threaded by a magnetic flux. The system can be described by an effective
one-impurity Anderson model with an energy- and flux-dependent density of
states. For specific values of the flux, this density of states vanishes at the
Fermi energy, yielding a controlled realization of the pseudogap Kondo effect.
The conductance and transmission phase shifts reflect a nontrivial interplay
between wave interference and interactions, providing clear signatures of
quantum phase transitions between Kondo and non-Kondo ground states.Comment: Published versio
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