Sung-Po Chao

Odd-parity superconductivity in Weyl semimetals

Unconventional superconducting states of matter are realized in the presence of strong spin orbit coupling. In particular, non degenerate bands can support odd parity superconductivity with rich topological content. Here we study whether this is the case for Weyl semimetals. These are systems whose low energy sector, in the absence of interactions, is described by linearly dispersing chiral fermions in three dimensions. The energy spectrum has nodes at an even number of points in the Brillouin zone. Consequently both intranodal finite momentum pairing and internodal BCS superconductivity are allowed. For local attractive interaction the finite momentum pairing state with chiral p-wave symmetry is found to be most favorable at finite chemical potential. The state is an analog of the superfluid

Long-range interaction induced phases in Weyl semimetals

^{3}

Kondo and charge fluctuation resistivity due to Anderson impurities in graphene

He A phase, with cooper pairs having finite center of mass momentum. For chemical potential at the node the state is preempted by a fully gapped charge density wave. For long range attraction the BCS state wins out for all values of the chemical potential.

Nonequilibrium transport of helical Luttinger liquids through a quantum dot

The interplay of spin orbit coupling and electron electron interaction condensing new phases of matter is an important new phenomena in solid state physics. In this paper we explore the nature of excitonic phases induced in Weyl semimetals by long range Coulomb repulsion. Its has been previously shown that short range repulsion leads to a ferromagnetic insulator while short range attraction results in a charge density wave state. Here we show the the charge density wave is the energetically favored state in the presence of long range repulsion.

Electric and thermoelectric transport in graphene and helical metal in finite magnetic fields

Motivated by experiments on ion irradiated graphene, we compute the resistivity of graphene with dilute impurities. In the local moment regime we employ the perturbation theory up to third order in the exchange coupling to determine the behavior at high temperatures within the Kondo model. Resistivity due to charge fluctuations is obtained within the mean field approach on the Anderson impurity model. Due to the linear spectrum of the graphene the Kondo behavior is shown to depend on the gate voltage applied. The location of the impurity on the graphene sheet is an important variable determining its effect on the Kondo scale and resistivity. Our results show that for chemical potential nearby the node the charge fluctuations is responsible for the observed temperature dependence of resistivity while away from the node the spin fluctuations take over. Quantitative agreement with experimental data is achieved if the energy of the impurity level varies linearly with the chemical potential.

Effect of an in-plane electric field on the magnetotransport in a helical metal

We study a steady state non-equilibrium transport between two interacting helical edge states of a two dimensional topological insulator, described by helical Luttinger liquids, through a quantum dot. For non-interacting dot the current is obtained analytically by including the self-energy correction to the dot Greens function. For interacting dot we use equation of motion method to study the influence of weak on-site Coulomb interaction on the transport. We find the metal-to-insulator quantum phase transition for attractive or repulsive interactions in the leads when the magnitude of the interaction strength characterized by a charge sector Luttinger parameter

Superconductivity in Weyl Semimetals

K

Excitonic Phases from Weyl Semi-Metals with short range interaction

goes beyond a critical value. The critical Luttinger parameter

Excitonic Phases of Weyl Semi-Metals with Coulomb Interaction

K_{cr}

Magnetoelectric and thermoelectric transport in graphene and helical metal: Effect of applied electric field

depends on the hoping strength between dot and the leads as well as the energy level of the dot with respect to the Fermi levels of the leads, ranging from weak interaction regime for dot level off resonance to strong interaction regime for dot in resonance with the equilibrium Fermi level. Nearby the transition various singular behaviors of current noise, dot density of state, and the decoherence rate (inverse of lifetime) of the dot are briefly discussed.