Inhomogeneous screening of gate electric field by interface states in graphene FETs.

The electronic states at graphene-SiO interface and their inhomogeneity is investigated using the back-gate-voltage dependence of local tunnel spectra acquired with a scanning tunneling microscope. The conductance spectra show two, or occasionally three, minima that evolve along the bias-voltage axis with the back gate voltage. This evolution is modeled using tip-gating and interface states.

Reversibility of superconducting nb weak links driven by the proximity effect in a quantum interference device.

We demonstrate the role of the proximity effect in the thermal hysteresis of superconducting constrictions. From the analysis of successive thermal instabilities in the transport characteristics of micron-size superconducting quantum interference devices with a well-controlled geometry, we obtain a complete picture of the different thermal regimes. These determine whether or not the junctions are hysteretic.

Evidence for topological surface states in metallic single crystals of Bi₂Te₃.

Bi2Te3 is a member of a new class of materials known as topological insulators which are supposed to be insulating in the interior and conducting on the surface. However, experimental verification of the conductive qualities of the surface states has been hindered by parallel bulk conductions. We report low temperature magnetotransport measurements on single crystal samples of Bi2Te3.

A temperature dependent tunneling study of the spin density wave gap in EuFe2As2 single crystals.

We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF).

Polaronic pseudogap in the metallic phase of La(0.625)Ca(0.375)MnO(3) thin films.

The electronic density of states (DOS) of La(0.625)Ca(0.375)MnO(3) (LCMO) strain-free epitaxial thin films with an insulator-metal transition temperature (T(IM)) of 250 K was probed using variable-temperature scanning tunneling microscopy and spectroscopy.

Compact two-dimensional coarse-positioner for scanning probe microscopes.

We report on the design and fabrication of a compact two-dimensional xy-positioner for scanning probe microscopes. This positioner uses three piezoelectric bimorphs in flexing or length-change mode by appropriate selection of electrodes and voltage polarities. One end of these bimorphs is fixed to a rectangular metal frame while on each of the free ends two sapphire disks are fixed which can slide against the polished plates of a platform movable in the xy-plane.