644 research outputs found
Large modulation of the Shubnikov-de Haas oscillations by the Rashba interaction at the LaAlO/SrTiO interface
We investigate the 2-dimensional Fermi surface of high-mobility
LaAlO/SrTiO interfaces using Shubnikov-de Haas oscillations. Our
analysis of the oscillation pattern underscores the key role played by the
Rashba spin-orbit interaction brought about by the breaking of inversion
symmetry, as well as the dominant contribution of the heavy /
orbitals on electrical transport. We furthermore bring into light the complex
evolution of the oscillations with the carrier density, which is tuned by the
field effect
A two-dimensional Fermi liquid with attractive interactions
We realize and study an attractively interacting two-dimensional Fermi
liquid. Using momentum resolved photoemission spectroscopy, we measure the
self-energy, determine the contact parameter of the short-range interaction
potential, and find their dependence on the interaction strength. We
successfully compare the measurements to a theoretical analysis, properly
taking into account the finite temperature, harmonic trap, and the averaging
over several two-dimensional gases with different peak densities
Preeminent role of the Van Hove singularity in the strong-coupling analysis of scanning tunneling spectroscopy for two-dimensional cuprates
In two dimensions the non-interacting density of states displays a Van Hove
singularity (VHS) which introduces an intrinsic electron-hole asymmetry, absent
in three dimensions. We show that due to this VHS the strong-coupling analysis
of tunneling spectra in high- superconductors must be reconsidered. Based
on a microscopic model which reproduces the experimental data with great
accuracy, we elucidate the peculiar role played by the VHS in shaping the
tunneling spectra, and show that more conventional analyses of strong-coupling
effects can lead to severe errors.Comment: 5 pages, 4 figure
Breakup of the Fermi surface near the Mott transition in low-dimensional systems
We investigate the Mott transition in weakly-coupled one-dimensional (1d)
fermionic chains. Using a generalization of Dynamic Mean Field Theory, we show
that the Mott gap is suppressed at some critical hopping . The
transition from the 1d insulator to a 2d metal proceeds through an intermediate
phase where the Fermi surface is broken into electron and hole pockets. The
quasiparticle spectral weight is strongly anisotropic along the Fermi surface,
both in the intermediate and metallic phases. We argue that such pockets would
look like `arcs' in photoemission experiments.Comment: REVTeX 4, 5 pages, 4 EPS figures. References added; problem with
figure 4 fixed; typos correcte
Tunneling spectra of strongly coupled superconductors: Role of dimensionality
We investigate numerically the signatures of collective modes in the
tunneling spectra of superconductors. The larger strength of the signatures
observed in the high-Tc superconductors, as compared to classical low-Tc
materials, is explained by the low dimensionality of these layered compounds.
We also show that the strong-coupling structures are dips (zeros in the d2I/dV2
spectrum) in d-wave superconductors, rather than the steps (peaks in d2I/dV2)
observed in classical s-wave superconductors. Finally we question the
usefulness of effective density of states models for the analysis of tunneling
data in d-wave superconductors.Comment: 8 pages, 6 figure
Heterovalent interlayers and interface states: an ab initio study of GaAs/Si/GaAs (110) and (100) heterostructures
We have investigated ab initio the existence of localized states and
resonances in abrupt GaAs/Si/GaAs (110)- and (100)-oriented heterostructures
incorporating 1 or 2 monolayers (MLs) of Si, as well as in the fully developed
Si/GaAs (110) heterojunction. In (100)-oriented structures, we find both
valence- and conduction-band related near-band edge states localized at the
Si/GaAs interface. In the (110) systems, instead, interface states occur deeper
in the valence band; the highest valence-related resonances being about 1 eV
below the GaAs valence-band maximum. Using their characteristic bonding
properties and atomic character, we are able to follow the evolution of the
localized states and resonances from the fully developed Si/GaAs binary
junction to the ternary GaAs/Si/GaAs (110) systems incorporating 2 or 1 ML of
Si. This approach also allows us to show the link between the interface states
of the (110) and (100) systems. Finally, the conditions for the existence of
localized states at the Si/GaAs (110) interface are discussed based on a
Koster-Slater model developed for the interface-state problem.Comment: REVTeX 4, 14 pages, 15 EPS figure
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
Multi-band Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8
Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and
PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2
~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap
distribution is strongly anisotropic, with Delta_2 predominantly seen when
scanning across unit-cell steps on the (001) sample surface. The spectra are
well-fitted by an anisotropic two-band BCS s-wave gap function. Our
spectroscopic data are confirmed by electronic heat capacity measurements which
also provide evidence for a twin-gap scenario.Comment: 5 pages, 4 figure
Hall effect in strongly correlated low dimensional systems
We investigate the Hall effect in a quasi one-dimensional system made of
weakly coupled Luttinger Liquids at half filling. Using a memory function
approach, we compute the Hall coefficient as a function of temperature and
frequency in the presence of umklapp scattering. We find a power-law correction
to the free-fermion value (band value), with an exponent depending on the
Luttinger parameter . At high enough temperature or frequency the
Hall coefficient approaches the band value.Comment: 7 pages, 3 figure
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