1,480 research outputs found
The Kondo Effect in the Unitary Limit
We observe a strong Kondo effect in a semiconductor quantum dot when a small
magnetic field is applied. The Coulomb blockade for electron tunneling is
overcome completely by the Kondo effect and the conductance reaches the
unitary-limit value. We compare the experimental Kondo temperature with the
theoretical predictions for the spin-1/2 Anderson impurity model. Excellent
agreement is found throughout the Kondo regime. Phase coherence is preserved
when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm
ring structure and the phase behavior differs from previous results on a
non-Kondo dot.Comment: 10 page
Gate-tunable band structure of the LaAlO-SrTiO interface
The 2-dimensional electron system at the interface between LaAlO and
SrTiO has several unique properties that can be tuned by an externally
applied gate voltage. In this work, we show that this gate-tunability extends
to the effective band structure of the system. We combine a magnetotransport
study on top-gated Hall bars with self-consistent Schr\"odinger-Poisson
calculations and observe a Lifshitz transition at a density of
cm. Above the transition, the carrier density of one
of the conducting bands decreases with increasing gate voltage. This surprising
decrease is accurately reproduced in the calculations if electronic
correlations are included. These results provide a clear, intuitive picture of
the physics governing the electronic structure at complex oxide interfaces.Comment: 14 pages, 4 figure
Electronic transport through a parallel--coupled triple quantum dot molecule: Fano resonances and bound states in the continuum
The electronic transport through a triple quantum dot molecule attached in
parallel to leads in presence of a magnetic flux is studied. Analytical
expressions of the linear conductance and density of states for the molecule in
equilibrium at zero temperature are obtained. As a consequence of quantum
interference, the conductance exhibits in general a Breit--Wigner and two Fano
resonances, the positions and widths of which are controlled by the magnetic
field. Every two flux quanta, there is an inversion of roles of the bonding and
antibonding states. For particular values of the magnetic flux and dot-lead
couplings, one or even both Fano resonances collapse and bound states in the
continuum (BIC's) are formed. The line broadenings of the molecular states are
examined as a function of the Aharonov--Bohm phase around the condition for the
formation of BIC's, finding resonances extremely narrow and robust against
variations of the magnetic field.Comment: 15 pages, 7 figure
Magnetically induced chessboard pattern in the conductance of a Kondo quantum dot
We quantitatively describe the main features of the magnetically induced
conductance modulation of a Kondo quantum dot -- or chessboard pattern -- in
terms of a constant-interaction double quantum dot model. We show that the
analogy with a double dot holds down to remarkably low magnetic fields. The
analysis is extended by full 3D spin density functional calculations.
Introducing an effective Kondo coupling parameter, the chessboard pattern is
self-consistently computed as a function of magnetic field and electron number,
which enables us to quantitatively explain our experimental data.Comment: 4 pages, 3 color figure
Correlation between Superconductivity, Band Filling and Electron Confinement at the LaAlO-SrTiO Interface
By combined top- and backgating, we explore the correlation of
superconductivity with band filling and electron confinement at the
LaAlO-SrTiO interface. We find that the top- and backgate voltages have
distinctly different effects on the superconducting critical temperature,
implying that the confining potential well has a profound effect on
superconductivity. We investigate the origin of this behavior by comparing the
gate-dependence of to the corresponding evolution of the band filling
with gate voltage. For several backgate voltages, we observe maximum to
consistently coincide with a kink in tuning the band filling for high topgate
voltage. Self-consistent Schr\"odinger-Poisson calculations relate this kink to
a Lifshitz transition of the second subband. These results establish a
major role for confinement-induced subbands in the phase diagram of SrTiO
surface states, and establish gating as a means to control the relative energy
of these states.Comment: 17 pages, 5 figure
Two decades of numerical modelling to understand long term fluvial archives: Advances and future perspectives
The development and application of numerical models to investigate fluvial sedimentary archives has increased during the last decades resulting in a sustained growth in the number of scientific publications with keywords, 'fluvial models', 'fluvial process models' and 'fluvial numerical models'. In this context we compile and review the current contributions of numerical modelling to the understanding of fluvial archives. In particular, recent advances, current limitations, previous unexpected results and future perspectives are all discussed. Numerical modelling efforts have demonstrated that fluvial systems can display non-linear behaviour with often unexpected dynamics causing significant delay, amplification, attenuation or blurring of externally controlled signals in their simulated record. Numerical simulations have also demonstrated that fluvial records can be generated by intrinsic dynamics without any change in external controls. Many other model applications demonstrate that fluvial archives, specifically of large fluvial systems, can be convincingly simulated as a function of the interplay of (palaeo) landscape properties and extrinsic climate, base level and crustal controls. All discussed models can, after some calibration, produce believable matches with real world systems suggesting that equifinality - where a given end state can be reached through many different pathways starting from different initial conditions and physical assumptions - plays an important role in fluvial records and their modelling. The overall future challenge lies in the development of new methodologies for a more independent validation of system dynamics and research strategies that allow the separation of intrinsic and extrinsic record signals using combined fieldwork and modelling
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