Large modulation of the Shubnikov-de Haas oscillations by the Rashba interaction at the LaAlO3_{3}/SrTiO3_{3} interface

We investigate the 2-dimensional Fermi surface of high-mobility LaAlO$_3$/SrTiO$_3$ 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 $d_{xz}$/$d_{yz}$ 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-$T_c$ 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 $t_{\perp}^{c2}$. 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 $K_{\rho}$. At high enough temperature or frequency the Hall coefficient approaches the band value.Comment: 7 pages, 3 figure