71 research outputs found
Quantum size effects on the perpendicular upper critical field in ultra-thin lead films
We report the thickness-dependent (in terms of atomic layers) oscillation
behavior of the perpendicular upper critical field in the
ultra-thin lead films at the reduced temperature (). Distinct
oscillations of the normal-state resistivity as a function of film thickness
have also been observed. Compared with the oscillation, the
shows a considerable large oscillation amplitude and a phase shift. The
oscillatory mean free path caused by quantum size effect plays a role in
oscillation.Comment: 4 pages, 4 figure
Nanotransformation and current fluctuations in exciton condensate junctions
We analyze the nonlinear transport properties of a bilayer exciton condensate
that is contacted by four metallic leads by calculating the full counting
statistics of electron transport for arbitrary system parameters. Despite its
formal similarity to a superconductor the transport properties of the exciton
condensate turn out to be completely different. We recover the generic features
of exciton condensates such as counterpropagating currents driven by excitonic
Andreev reflections and make predictions for nonlinear transconductance between
the layers as well as for the current (cross)correlations and generalized
Johnson-Nyquist relationships. Finally, we explore the possibility of
connecting another mesoscopic system (in our case a quantum point contact) to
the bottom layer of the exciton condensate and show how the excitonic Andreev
reflections can be used for transforming voltage at the nanoscale.Comment: 5 pages, 4 figures, accepted by PR
Kondo effect and spin-active scattering in ferromagnet-superconductor junctions
We study the interplay of superconducting and ferromagnetic correlations on
charge transport in different geometries with a focus on both a quantum point
contact as well as a quantum dot in the even and the odd state with and without
spin-active scattering at the interface. In order to obtain a complete picture
of the charge transport we calculate the full counting statistics in all cases
and compare the results with experimental data. We show that spin-active
scattering is an essential ingredient in the description of quantum point
contacts. This holds also for quantum dots in an even charge state whereas it
is strongly suppressed in a typical Kondo situation. We explain this feature by
the strong asymmetry of the hybridisations with the quantum dot and show how
Kondo peak splitting in a magnetic field can be used for spin filtering. For
the quantum dot in the even state spin-active scattering allows for an
explanation of the experimentally observed mini-gap feature.Comment: 14 pages, 7 figures, accepted by PR
Structural and magneto-transport properties of electrodeposited bismuth nanowires
Arrays of semimetallic Bi nanowires have been successfully fabricated by electrodeposition. Each nanowire consists of elongated Bi grains along the wire direction. Very large positive magnetoresistance of 300% at low temperatures and 70% at room temperature with quasilinear field dependence has been observed. These features are desirable for wide-range field sensing applications. © 1998 American Institute of Physics
High-frequency transport in -type Si/SiGe heterostructures studied with surface acoustic waves in the quantum Hall regime
The interaction of surface acoustic waves (SAW) with -type
Si/SiGe heterostructures has been studied for SAW frequencies
of 30-300 MHz. For temperatures in the range 0.71.6 K and magnetic fields
up to 7 T, the SAW attenuation coefficient and velocity change were found to oscillate with filling factor. Both the real and
imaginary components of the high-frequency conductivity have been
determined and compared with quasi-dc magnetoresistance measurements at
temperatures down to 33 mK. By analyzing the ratio of to ,
carrier localization can be followed as a function of temperature and magnetic
field. At =0.7 K, the variations of , and
with SAW intensity have been studied and can be explained by heating of the two
dimensional hole gas by the SAW electric field. Energy relaxation is found to
be dominated by acoustic phonon deformation potential scattering with weak
screening.Comment: Accepted for publication in PR
Spin precession observation in quantum corrections to resistance of Si 0:7 Ge 0:3 =Si 0:2 Ge 0:8 heterostructure with 2DHG
Abstract The two-dimensional hole gas (2DHG) magnetoresistivity of a Si0:7Ge0:3=Si0:2Ge0:8 heterostructure in a wide range of temperatures T = 0:335-20 K and transport currents I = 100-50 A is measured. In the vicinity of zero magnetic ÿeld, a sharp and positive in sign feature on smooth negative magnetoresistance is observed at the lowest temperatures. The amplitude of this feature quickly fades with increasing temperature and transport current. For the analysis of the experimental data the theory of weak localization for 2DHG is applied. The values of so and tr obtained are used for the ÿrst time to deÿne zero magnetic ÿeld splitting in the hole energy spectrum for a Si0:7Ge0:3=Si0:2Ge0:8 heterostructure: = 2:97 meV.
Applying voltage sources to a Luttinger liquid with arbitrary transmission
The Landauer approach to transport in mesoscopic conductors has been
generalized to allow for strong electronic correlations in a single-channel
quantum wire. We describe in detail how to account for external voltage sources
in adiabatic contact with a quantum wire containing a backscatterer of
arbitrary strength. Assuming that the quantum wire is in the Luttinger liquid
state, voltage sources lead to radiative boundary conditions applied to the
displacement field employed in the bosonization scheme. We present the exact
solution of the transport problem for arbitrary backscattering strength at the
special Coulomb interaction parameter g=1/2.Comment: 9 pages REVTeX, incl 2 fig
Role of the surface states in the magnetotransport properties of ultrathin bismuth films
Large Magnetoresistance and Finite-Size Effects in Electrodeposited Single-Crystal Bi Thin Films
Trigonal-axis oriented single-crystal Bi thin films have been made by electrodeposition followed by suitable annealing. Very large magnetoresistance with ratios as much as 1500 at 5 K and 2.9 at 300 K under 5 T, Shubnikov-de Haas oscillations, and finite-size effects have been observed. © 1999 The American Physical Society
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