M.P. Stehno

Gate-Tunable Band Structure of the LaAlO3−SrTiO3 Interface

The two-dimensional electron system at the interface between LaAlO_{3} and SrTiO_{3} has several unique properties that can be tuned by an externally applied gate voltage. In this work, we show that this gate tunability extends to the effective band structure of the system. We combine a magnetotransport study on top-gated Hall bars with self-consistent Schrödinger-Poisson calculations and observe a Lifshitz transition at a density of 2.9×10^{13}cm^{-2}. Above the transition, the carrier density of one of the conducting bands decreases with increasing gate voltage. This surprising decrease is accurately reproduced in the calculations if electronic correlations are included. These results provide a clear, intuitive picture of the physics governing the electronic structure at complex-oxide interfaces.

In-situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects

Combined in situ x-ray photoemission spectroscopy, scanning tunneling spectroscopy, and angle resolved photoemission spectroscopy of molecular beam epitaxy grown Bi 2 Te 3 on lattice mismatched substrates reveal high quality stoichiometric thin films with topological surface states without a contribution from the bulk bands at the Fermi energy. The absence of bulk states at the Fermi energy is achieved without counterdoping. We observe that the surface morphology and electronic band structure of Bi 2 Te 3 are not affected by in vacuo storage and exposure to oxygen, whereas major changes are observed when exposed to ambient conditions. These films help define a pathway towards intrinsic topological devices.

Gate-Tunable Transport Properties of In Situ Capped Bi2Te3 Topological Insulator Thin Films

Combining of the ability to prepare high-quality, intrinsic Bi2Te3 topological insulator thin films of low carrier density with in situ protective capping, a pronounced, gate-tunable change in transport properties of Bi2Te3 thin films is demonstrated. Using a back gate, the carrier density is tuned by a factor of ≈7 in an Al2O3 capped Bi2Te3 sample and by a factor of ≈2 in Te capped Bi2Te3 films. Full depletion of bulk carriers is achieved, which allows access to the topological transport regime dominated by surface state conduction. When the Fermi level is placed in the bulk band gap, the presence of two coherent conduction channels associated with the two decoupled surfaces is observed. The magnetotransport results show that the combination of capping layers and electrostatic tuning of the Fermi level provide a technological platform to investigate the topological properties of surface states in transport experiments and pave the way toward the implementation of a variety of topological quantum devices.

Scaling universality at the dynamic vortex Mott transition

The cleanest way to observe a dynamic Mott insulator-to-metal transition (DMT) without the interference from disorder and other effects inherent to electronic and atomic systems, is to employ the vortex Mott states formed by superconducting vortices in a regular array of pinning sites. Here, we report the critical behavior of the vortex system as it crosses the DMT line, driven by either current or temperature. We find universal scaling with respect to both, expressed by the same scaling function and characterized by a single critical exponent coinciding with the exponent for the thermodynamic Mott transition. We develop a theory for the DMT based on the parity reflection-time reversal (PT) symmetry breaking formalism and find that the nonequilibrium-induced Mott transition has the same critical behavior as the thermal Mott transition. Our findings demonstrate the existence of physical systems in which the effect of a nonequilibrium drive is to generate an effective temperature and hence the transition belonging in the thermal universality class.

Conduction spectroscopy of a proximity induced superconducting topological insulator

The combination of superconductivity and the helical spin-momentum locking at the surface state of a topological insulator (TI) has been predicted to give rise to p-wave superconductivity and Majorana bound states. The superconductivity can be induced by the proximity effect of a an s-wave superconductor (S) into the TI. To probe the superconducting correlations inside the TI, dI/dV spectroscopy has been performed across such S-TI interfaces. Both the alloyed Bi

Manipulating Electronic States at Oxide Interfaces Using Focused Micro X-Rays from Standard Lab Sources

_{1.5}

In Situ Characterization Tools for Bi 2 Te 3 Topological Insulator Nanomaterials

Sb

Stencil lithography of superconducting contacts on MBE-grown topological insulator thin films

_{0.5}

Modified spin relaxation mechanism by tunable coupling between interfacial two-dimensional electron gases in correlated oxide heterostructures

Te

Correlation between superconductivity, band filling, and electron confinement at the LaAlO3/SrTiO3 interface

_{1.7}