702 research outputs found
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
Signatures of quantum phase transitions in parallel quantum dots: Crossover from local-moment to underscreened spin-1 Kondo physics
We study a strongly interacting "quantum dot 1" and a weakly interacting "dot
2" connected in parallel to metallic leads. Gate voltages can drive the system
between Kondo-quenched and non-Kondo free-moment phases separated by
Kosterlitz-Thouless quantum phase transitions. Away from the immediate vicinity
of the quantum phase transitions, the physical properties retain signatures of
first-order transitions found previously to arise when dot 2 is strictly
noninteracting. As interactions in dot 2 become stronger relative to the
dot-lead coupling, the free moment in the non-Kondo phase evolves smoothly from
an isolated spin-one-half in dot 1 to a many-body doublet arising from the
incomplete Kondo compensation by the leads of a combined dot spin-one. These
limits, which feature very different spin correlations between dot and lead
electrons, can be distinguished by weak-bias conductance measurements performed
at finite temperatures.Comment: 7 pages, 7 figures. Accepted for publication in Phys. Rev.
Zero-field Kondo splitting and quantum-critical transition in double quantum dots
Double quantum dots offer unique possibilities for the study of many-body
correlations. A system containing one Kondo dot and one effectively
noninteracting dot maps onto a single-impurity Anderson model with a structured
(nonconstant) density of states. Numerical renormalization-group calculations
show that while band filtering through the resonant dot splits the Kondo
resonance, the singlet ground state is robust. The system can also be
continuously tuned to create a pseudogapped density of states and access a
quantum critical point separating Kondo and non-Kondo phases.Comment: 4 pages, 4 figures; Accepted for publication in Physical Review
Letter
Transmission in double quantum dots in the Kondo regime: Quantum-critical transitions and interference effects
We study the transmission through a double quantum-dot system in the Kondo
regime. An exact expression for the transmission coefficient in terms of fully
interacting many-body Green's functions is obtained. By mapping the system into
an effective Anderson impurity model, one can determine the transmission using
numerical renormalization-group methods. The transmission exhibits signatures
of the different Kondo regimes of the effective model, including an unusual
Kondo phase with split peaks in the spectral function, as well as a
pseudogapped regime exhibiting a quantum critical transition between Kondo and
unscreened phases.Comment: 4 pages, 3 figures; Submitted to Physica E (EP2DS-17 proceedings,
oral presentation), updated Ref
Interplay of Kondo, Zeeman, and interference effects
We study the effect of a magnetic field in the Kondo regime of a double-
quantum-dot system consisting of a strongly correlated dot (the “side dot”)
coupled to a second, noninteracting dot that also connects two external leads.
We show, using the numerical renormalization group, that application of an in-
plane magnetic field sets up a subtle interplay between electronic
interference, Kondo physics, and Zeeman splitting with nontrivial consequences
for spectral and transport properties. The value of the side-dot spectral
function at the Fermi level exhibits a nonuniversal field dependence that can
be understood using a form of the Friedel sum rule that appropriately accounts
for the presence of an energy- and spin-dependent hybridization function. The
applied field also accentuates the exchange-mediated interdot coupling, which
dominates the ground state at intermediate fields leading to the formation of
antiparallel magnetic moments on the dots. By tuning gate voltages and the
magnetic field, one can achieve complete spin polarization of the linear
conductance between the leads, raising the prospect of applications of the
device as a highly tunable spin filter. The system's low-energy properties are
qualitatively unchanged by the presence of weak on-site Coulomb repulsion
within the second dot
Interplay of Kondo, Zeeman, and interference effects
We study the effect of a magnetic field in the Kondo regime of a double-
quantum-dot system consisting of a strongly correlated dot (the “side dot”)
coupled to a second, noninteracting dot that also connects two external leads.
We show, using the numerical renormalization group, that application of an in-
plane magnetic field sets up a subtle interplay between electronic
interference, Kondo physics, and Zeeman splitting with nontrivial consequences
for spectral and transport properties. The value of the side-dot spectral
function at the Fermi level exhibits a nonuniversal field dependence that can
be understood using a form of the Friedel sum rule that appropriately accounts
for the presence of an energy- and spin-dependent hybridization function. The
applied field also accentuates the exchange-mediated interdot coupling, which
dominates the ground state at intermediate fields leading to the formation of
antiparallel magnetic moments on the dots. By tuning gate voltages and the
magnetic field, one can achieve complete spin polarization of the linear
conductance between the leads, raising the prospect of applications of the
device as a highly tunable spin filter. The system's low-energy properties are
qualitatively unchanged by the presence of weak on-site Coulomb repulsion
within the second dot
Absence of Myocardial Thyroid Hormone Inactivating Deiodinase Results in Restrictive Cardiomyopathy in Mice
Cardiac injury induces myocardial expression of the thyroid hormone inactivating type 3 deiodinase (D3), which in turn dampens local thyroid hormone signaling. Here, we show that the D3 gene (Dio3) is a tissue-specific imprinted gene in the heart, and thus, heterozygous D3 knockout (HtzD3KO) mice constitute a model of cardiac D3 inactivation in an otherwise systemically euthyroid animal. HtzD3KO newborns have normal hearts but later develop restrictive cardiomyopathy due to cardiac-specific increase in thyroid hormone signaling, including myocardial fibrosis, impaired myocardial contractility, and diastolic dysfunction. In wild-type littermates, treatment with isoproterenol-induced myocardial D3 activity and an increase in the left ventricular volumes, typical of cardiac remodeling and dilatation. Remarkably, isoproterenol-treated HtzD3KO mice experienced a further decrease in left ventricular volumes with worsening of the diastolic dysfunction and the restrictive cardiomyopathy, resulting in congestive heart failure and increased mortality. These findings reveal crucial roles for Dio3 in heart function and remodeling, which may have pathophysiologic implications for human restrictive cardiomyopathy
Doubt and Excitement:An Experiential Learning Approach to Teaching the Practice of Qualitative Research
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