E. Lahoud

Proximity-induced superconductivity in topological Bi2Te2Se and Bi2Se3films: Robust zero-energy bound state possibly due to Majorana fermions

Point contact conductance measurements on topological

Point-contact spectroscopy of Cu0.2Bi2Se3single crystals

Bi_2Te_2Se

Evolution of the Fermi surface of a doped topological insulator with carrier concentration

and

Emergence of a Novel Pseudogap Metallic State in a Disordered 2D Mott Insulator

Bi_2Se_3

Internal pressure in superconducting Cu-intercalatedBi2Se3

films reveal a signature of superconductivity below 2-3 K. In particular, critical current dips and a robust zero bias conductance peak are observed. The latter suggests the presence of zero energy bound states which could be assigned to Majorana Fermions in an unconventional topological superconductor. We attribute these novel observations to proximity induced local superconductivity in the films by small amounts of superconducting Bi inclusions or segregation to the surface, and provide supportive evidence for these effects.

Sensitivity of angle-resolved photoemission to short-range antiferromagnetic correlations

We report point contact measurements in high quality single crystals of Cu0.2Bi2Se3. We observe three different kinds of spectra: (1) Andreev-reflection spectra, from which we infer a superconducting gap size of 0.6mV; (2) spectra with a large gap which closes above Tc at about 10K; and (3) tunneling-like spectra with zero-bias conductance peaks. These tunneling spectra show a very large gap of ~2meV (2Delta/KTc ~ 14).

Anisotropic scattering rate in Fe-substituted Bi2Sr2Ca(Cu1-xFex)2O8+δ

In an ideal bulk topological-insulator (TI) conducting surface states protected by time reversal symmetry enfold an insulating crystal. However, the archetypical TI, Bi2Se3, is actually never insulating; it is in fact a relatively good metal. Nevertheless, it is the most studied system among all the TIs, mainly due to its simple band-structure and large spin-orbit gap. Recently it was shown that copper intercalated Bi2Se3 becomes superconducting and it was suggested as a realization of a topological superconductor (TSC). Here we use a combination of techniques that are sensitive to the shape of the Fermi surface (FS): the Shubnikov-de Haas (SdH) effect and angle resolved photoemission spectroscopy (ARPES) to study the evolution of the FS shape with carrier concentration, n. We find that as n increases, the FS becomes 2D-like. These results are of crucial importance for understanding the superconducting properties of CuxBi2Se3.

ARPES sensitivity to short-range antiferromagnetic correlations

It is well established that for non-interacting electrons, increasing disorder drives a metal into a gapless localized Anderson insulator. While in three dimensions a threshold in disorder must be crossed for the transition, in two dimensions and lower, the smallest amount of disorder destabilizes the metal. The nature of the metal-insulator transition in an interacting system remains unresolved. Here we explore the effect of disorder on a strongly correlated Mott insulator without changing the carrier concentration. Angle resolved photoemission spectroscopy (ARPES) measurements on copper intercalated single crystals of the layered dichalcogenide 1T-TaS2 reveal the presence of new delocalized states within the Mott gap. This is the first experimental realization of a novel disorder-induced metal that was theoretically predicted to exist between the Mott insulator and Anderson insulator.

Emergent Metal in Disordered Two Dimensional Mott Insulator

Angle-resolved photoemission spectroscopy is used to study the band-structure of superconducting electrochemically intercalated Cu

Bulk versus surface contributions to the Shubnikov-de Haas Effect

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