David Carpentier

Topological index for periodically driven time-reversal invariant 2D systems.

We define a new Z2-valued index to characterize the topological properties of periodically driven two dimensional crystals when the time-reversal symmetry is enforced. This index is associated with a spectral gap of the evolution operator over one period of time. When two such gaps are present, the Kane-Mele index of the eigenstates with eigenvalues between the gaps is recovered as the difference of the gap indices. This leads to an expression for the Kane-Mele invariant in terms of the Wess-Zumino amplitude. We illustrate the relation of the new index to the edge states in finite geometries by numerically solving an explicit model on the square lattice that is periodically driven in a time-reversal invariant way.

Two-Dimensional Anisotropic Non-Fermi-Liquid Phase of Coupled Luttinger Liquids

Using bosonization techniques, we show that strong forward scattering interactions between one-dimensional spinless Luttinger liquids (LL) can stabilize a phase where charge-density wave, superconducting, and transverse single particle hopping perturbations are irrelevant. This new phase retains its LL-like properties in the directions of the chains, but with relations between exponents modified by the transverse interactions, whereas it is a perfect insulator in the transverse direction. The mechanism that stabilizes this phase is strong transverse charge-density wave fluctuations at incommensurate wave vector, which frustrates crystal formation by preventing lock-in of the in-chain density waves.

Disordered XY models and Coulomb gases: renormalization via traveling waves

We present a novel RG approach to 2D random XY models using direct and replicated Coulomb gas methods. By including fusion of environments (charge fusion in the replicated CG) it follows the distribution of local disorder, found to obey a Kolmogorov non linear equation (KPP) with traveling wave solutions. At low T and weak disorder it yields a glassy XY phase with broad distributions and precise connections to Derridas GREM. Finding marginal operators at the disorder-induced transition is related to the front velocity selection problem in KPP equations yielding new critical behaviour. The method is applied to critical random Dirac problems.

Momentum-resolved tunneling between Luttinger liquids

We study tunneling between two nearby cleaved edge quantum wires in a perpendicular magnetic field. Due to Coulomb forces between electrons, the wires form a strongly interacting pair of Luttinger liquids. We calculate the low-temperature differential tunneling conductance, in which singular features map out the dispersion relations of the fractionalized quasiparticles of the system. The velocities of several such spin-charge separated excitations can be explicitly observed. Moreover, the proposed measurement directly demonstrates the splintering of the tunneling electrons into a multiparticle continuum of these quasiparticles, carrying separately charge from spin. A variety of corrections to the simple Luttinger model are also discussed. Our results are in agreement with recent experiments by Auslaender et al. [Science 295. 825 (2002)].

Tunable thermopower in a graphene-based topological insulator

Gapped materials can possess unique topological properties and robust propagating states at their boundaries. The associated transport properties allow fascinating new electronic and spintronic devices. Recently a new class of spin-polarized edge states has been discovered in the so-called topological insulators. However, probing these edge states through transport has proved to be challenging. We explore the properties of a new putative material: a graphene layer with a random deposition of Indium adatoms at its surface. While this system is, by construction, very disordered, we nd that it exhibits an extremely stable topological quantum spin Hall phase with no signature of the spatial inhomogeneities of the adatom conguration. This robustness opens the route to a much easier experimental realization of this topological phase. We additionally nd this material to be a very promising candidate for thermopower generation with a target temperature tunable from 1 to 80 K and an eciency ZT 1. PACS numbers:

On the disorder-driven quantum transition in three-dimensional relativistic metals

The Weyl semimetals are topologically protected from a gap opening against weak disorder in three dimensions. However, a strong disorder drives this relativistic semimetal through a quantum transition towards a diffusive metallic phase characterized by a finite density of states at the band crossing. This transition is usually described by a perturbative renormalization group in

Field theory for generalized Shastry-Sutherland models

d=2+varepsilon

New quantum transition in Weyl semimetals with correlated disorder

of a

Measuring overlaps in mesoscopic spin glasses via conductance fluctuations.

U(N)

On the origin of minimal conductivity at a band crossing

Gross-Neveu model in the limit