endra K. Jain

Evidence for electron-electron interaction in topological insulator thin films

We consider in our work single crystal thin films of Bi(2)Se(3), grown by molecular beam epitaxy, both with and without Pb doping. Angle-resolved photoemission data demonstrate topological surface states with a Fermi level lying inside the bulk band gap in the Pb-doped films. Transport data show weak localization behavior, as expected for a thin film in the two-dimensional limit (when the thickness is smaller than the inelastic mean free path), but a detailed analysis within the standard theoretical framework of diffusive transport shows that the temperature and magnetic field dependences of resistance cannot be reconciled in a theory that neglects inter-electron interactions. We demonstrate that an excellent account of quantum corrections to conductivity is achieved when both disorder and interaction are taken into account. These results clearly demonstrate that it is crucial to include electron-electron interaction for a comprehensive understanding of diffusive transport in topological insulators. While both the ordinary bulk and the topological surface states presumably participate in transport, our analysis does not allow a clear separation of the two contributions.

Fractional quantum Hall effect in graphene

Unlike regular electron spin, the pseudospin degeneracy of Fermi points in graphene does not couple directly to magnetic field. Therefore graphene provides a natural vehicle to observe the integral and fractional quantum Hall physics in an elusive limit analogous to zero Zeeman splitting in GaAs systems. This limit can exhibit new integral plateaus arising from interactions, large pseudoskyrmions, fractional sequences, even/odd numerator effects, composite-fermion pseudoskyrmions, and a pseudospin-singlet composite-fermion Fermi sea. It is stressed that the Dirac nature of the

Superconducting proximity effect and possible evidence for Pearl vortices in a candidate topological insulator

B=0

The Composite Fermion: A Quantum Particle and Its Quantum Fluids

spectrum, which induces qualitative changes in the overall spectrum, has no bearing on the fractional quantum Hall effect in the

Mechanism for Current Saturation and Energy Dissipation in Graphene Transistors

n=0

Proximity-Induced Superconductivity in Nanowires: Minigap State and Differential Magnetoresistance Oscillations

Landau level of graphene. The second Landau level of graphene is predicted to show more robust fractional quantum Hall effect than the second Landau level of GaAs.

Theoretical search for the nested quantum Hall effect of composite fermions

We report the observation of the superconducting proximity effect in nanoribbons of a candidate topological insulator (Bi2Se3) which is interfaced with superconducting (tungsten) contacts. We observe a supercurrent and multiple Andreev reflections for channel lengths that are much longer than the inelastic and diffusive thermal lengths deduced from normal state transport. This suggests that the proximity effect couples preferentially to a ballistic surface transport channel, even in the presence of a coexisting diffusive bulk channel. When a magnetic field is applied perpendicular to the plane of the nanoribbon, we observe magnetoresistance oscillations that are periodic in magnetic field. Quantitative comparison with a model of vortex blockade relates the occurrence of these oscillations to the formation of Pearl vortices in the region of proximity induced superconductivity.

Cooper instability of composite fermions

Discovery of new particles is not usually associated with condensed matter physics, because, at one level, we already know all the particles that go into the Hamiltonian—namely, electrons and ions. But it is a most profound fact of nature—indeed the very reason why physics can make progress at many different levels—that strongly interacting particles reorganize themselves to become more weakly coupled particles of a new kind. Often they are simple bound states of the old particles. But sometimes they are fantastically complicated collective objects (for example, solitons) that nonetheless behave as legitimate particles, with well‐defined charge, spin, statistics, and other properties we attribute to particles.

Zero-Field Dissipationless Chiral Edge Transport and the Nature of Dissipation in the Quantum Anomalous Hall State

From a combination of careful and detailed theoretical and experimental studies, we demonstrate that the Boltzmann theory including all scattering mechanisms gives an excellent account, with no adjustable parameters, of high electric field transport in single as well as double-oxide graphene transistors. We further show unambiguously that scattering from the substrate and superstrate surface optical phonons governs the high-field transport and heat dissipation over a wide range of experimentally relevant parameters. Models that neglect surface optical phonons altogether or treat them in a simple phenomenological manner are inadequate. We outline possible strategies for achieving higher current and complete saturation in graphene devices.

Rotons of composite fermions: Comparison between theory and experiment

We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the minigap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We suggest that the minigap phase as well as the periodic oscillations originate from a coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or the application of a magnetic field.