Electrical and thermal transport throughα-T3NIS junction.

We investigate the electrical and thermal transport properties of theα-T3based normal metal-insulator-superconductor (NIS) junction using Blonder-Tinkham-Klapwijk theory. We show that the tunneling conductance of the NIS junction is an oscillatory function of the effective barrier potential (χ) of the insulating region up to a thin barrier limit. The periodicity and the amplitudes of the oscillations largely depend on the values ofαand the gate voltage of the superconducting region, namely,U0. Further, the periodicity of the oscillation changes fromπtoπ/2as we increaseU0. To assess the thermoelectric performance of such a junction, we have computed the Seebeck coefficient, the thermoelectric figure of merit, maximum power output, efficiency at the maximum output power of the system, and the thermoelectric cooling of the NIS junction as a self-cooling device. Our results on the thermoelectric cooling indicate practical realizability and usefulness for using our system as efficient cooling detectors, sensors, etc and hence could be crucial to the experimental success of the thermoelectric applications of such junction devices. Furthermore, for anα-T3lattice, whose limiting cases denote a graphene or a dice lattice, it is interesting to ascertain which one is more suitable as a thermoelectric device and the answer seems to depend on theU0. We observe that for anα-T3lattice corresponding toU0=0, graphene (α = 0) is more feasible for constructing a thermoelectric device, whereas forU0≫EF, the dice lattice (α = 1) has a larger utility.

Topological phase transition induced by band structure modulation in a Chern insulator.

We study a systematic evolution of the topological properties of a Chern insulator upon smooth variation of a hopping parameter (t1) of the electrons among a pair of nearest neighbour sites on a honeycomb lattice, while keeping the other two hopping terms (t) fixed. In the absence of a Haldane flux, the tuning oft1results in gradual shifting of the Dirac cones which eventually merge into one at theMpoint in the Brillouin zone (BZ) att1= 2twith a gapless semi-Dirac dispersion at low energies. In the presence of a Haldane flux, the system becomes a Chern insulator fort1< 2t, but turns gapless att1= 2twith the semi-Dirac dispersion being transformed to an anisotropic Dirac one. The spectrum eventually gaps out and transforms into a trivial insulator fort1> 2t. The Chern number phase diagram obtained via integrating the Berry curvature over the BZ shows a gradual shrinking of the 'topological' lobes, and vanishes just beyondt1= 2t, where a small but a finite Berry curvature still exists. Thus, there is a phase transition from a topological phase to a trivial phase across the semi-Dirac point (t1= 2t). The vanishing of the anomalous Hall conductivity plateau and the merger of the chiral edge states with the bulk bands near theMpoint provide robust support of the observed phase transition.