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The topological property in one dimension (1D) is protected by symmetry. Based on a concrete model, we show that since a 1D topological model usually contain two of the three Pauli matrix, the left one automatically become the protecting symmetry. We study the effect of disorder preserving or breaking the symmetry and show the nature of symmetry protecting in the 1D topological phase. Based on the 1D topological model, a stable quantum pumping can be constructed, which is topologically nontrivial and can be characterized by the Chern number. By calculating the instantaneous local current we show that an integer charge is pumped across a periodic chain in a cyclic process. Also on an open chain, an edge state can be transferred to the other edge by the quantum pumping. Furthermore we find that not only the quantum pumping is stable to on-site disorder, but also can be induced by it. These results may be realized experimentally using quasicrystals.
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We consider transport properties of a two dimensional topological insulator in a double quantum point contact geometry in presence of a time-dependent external field. In the proposed setup an external gate is placed above a single constriction and it couples only with electrons belonging to the top edge. This asymmetric configuration and the presence of an ac signal allow for a quantum pumping mechanism, which, in turn, can generate finite heat and charge currents in an unbiased device configuration. A microscopic model for the coupling with the external time-dependent gate potential is developed and the induced finite heat and charge currents are investigated. We demonstrate that in the non-interacting case, heat flow is associated with a single spin component, due to the helical nature of the edge states, and therefore a finite and polarized heat current is obtained in this configuration. The presence of e-e interchannel interactions strongly affects the current signal, lowering the degree of polarization of the system. Finally, we also show that separate heat and charge flows can be achieved, varying the amplitude of the external gate.
By using the self-consistent Born approximation, we investigate disorder effect induced by the short-range impurities on the band-gap in two-dimensional Dirac systems with the higher order terms in momentum. Starting from the Bernevig-Hughes-Zhang (BHZ) model, we calculate the density-of-states as a function of the disorder strength. We show that due to quadratic corrections to the Dirac Hamiltonian, the band-gap is always affected by the disorder even if the system is gapless in the clean limit. Finally, we explore the disorder effects by using an advanced effective Hamiltonian describing the side maxima of the valence subband in HgTe~quantum wells. We show that the band-gap and disorder-induced topological phase transition in the real structures may differ significantly from those predicted within the BHZ model.
Electron tunneling through a two stage Kondo system constituted by a double quantum-dot molecule side coupled to a quantum wire, under the effect of a finite external potential is studied. We found that $I$-$V$ characteristic shows a negative differential conductance region induced by the electronic correlation. This phenomenon is a consequence of the properties of the two stage Kondo regime under the effect of an external applied potential that takes the system out of equilibrium. The problem is solved using the mean-field finite-$U$ slave-boson formalism.
We study the generation of an electromagnetic current in monolayer graphene immersed in a weak perpendicular magnetic field and radiated with linearly polarized monochromatic light. Such a current emits Bremsstrahlung radiation with the same amplitude above and below the plane of the sample, in the latter case consistent with the small amount of light absorption in the material. This mechanism could be an important contribution for the reflexion of light phenomenon in graphene.
This paper has been withdrawn by the author and replaced by arXiv:0809.4751
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