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We concentrate on the skin effects and topological properties in the multilayer non-Hermitian Su–Schrieffer–Heeger (SSH) structure, by taking into account the nonreciprocal couplings between the different sublattices in the unit cells. Following the detailed demonstration of the theoretical method, we find that in this system, the skin effects and topological phase transitions induced by nonreciprocal couplings display the apparent parity effect, following the increase of the layer number of this SSH structure. On the one hand, the skin effect is determined by the parity of the layer number of this SSH system, as well as the parity of the band index of the bulk states. On the other hand, for the topological edge modes, such an interesting parity effect can also be observed clearly. Next, when the parameter disorders are taken into account, the zero-energy edge modes in the odd-layer structures tend to be more robust, whereas the other edge modes are easy to be destroyed. In view of these results, it can be ascertained that the findings in this work promote to understand the influences of nonreciprocal couplings on the skin effects and topological properties in the multilayer SSH lattices. [ABSTRACT FROM AUTHOR]

We theoretically investigate the topological phase transition of the antiferromagnetic Rashba nanowire, by considering it to be subject to the superconducting proximity effect and longitudinal magnetic field. We see that the antiferromagnetic order enriches the topological superconducting phase transition and causes Majorana bound states (MBSs) to form in more parameter regions, compared to the normal Rashba nanowire. Even in the absence of magnetic field, antiferromagnetic order can also induce the formation of MBSs through introducing the alternative phase transition manner. More importantly, the antiferromagnetic-induced MBSs can be less influenced by the perturbation of parameter disorders, including the intersite couplings and AFM order of the nanowire. Their signature is still robust when the MBSs contributed by the uniform magnetic field are destroyed by disorders. We then believe that the findings in this work can be helpful in utilizing antiferromagnetic nanowires to experimentally achieve the MBSs for future topological quantum computation. [ABSTRACT FROM AUTHOR]

We investigate the conductance properties in the quantum-dot structure with the nonlocal coupling of Majorana bound states (MBSs) to the dot. Results show that two molecular states of the MBS-coupled quantum dot can be degenerate at the Fermi level, in the case of appropriate structural parameters. Interestingly, the level degeneracy exactly leads to the occurrence of resonant tunneling. Further investigation demonstrates that double resonant tunneling phenomenon occurs as local magnetic flux is incorporated. Moreover, the Coulomb interaction in this system makes the double resonant tunneling more apparent. We believe that these results can help increase understanding of the quantum transport characteristics due to the nonlocal coupling between the quantum dot and MBSs. [ABSTRACT FROM AUTHOR]

By introducing the P T -symmetric complex potentials, we investigate the properties of the band structure of the bowtie lattice with P T symmetry. It is found that the complex potentials directly lead to the enhancement of the energy-band overlap, including the occurrence of the threefold degeneracy. Meanwhile, the flat band is destroyed gradually and the P T -symmetry breaking occurs. When the two-dimensional lattice is cut into one-dimensional ribbons, the effect of the complex potentials is tightly dependent on the types of the ribbon edges, i.e., zigzag or armchair. For the case of armchair ribbon, the roles of the P T -symmetric potentials are more dependent on its width. We believe that this work is useful for understanding the band structures of the P T -symmetric bowtie-lattice systems. [ABSTRACT FROM AUTHOR]

We report a theoretical study about the spin-dependent electron transport through a two-arm mesoscopic circuit in which two protein-like single-helical molecules connect serially with two normal metallic leads, respectively. Based on an effective-model Hamiltonian, the spin polarization is evaluated using the Landauer-Büttiker formula. Our results reveal that in comparison with the single-arm case, the spin-polarization efficiency can be enhanced in this system, by adjusting the length ratio of two molecules and the molecule-lead coupling manner. Besides, when local magnetic flux is introduced, the Aharonov-Bohm effect makes a nontrivial contribution to the spin polarization. These findings can be helpful for building the helical-molecule-based spin filters. [ABSTRACT FROM AUTHOR]

We investigate the electron transport through a graphene quantum dot with one line defect, by coupling the dot to two normal metallic leads. It is found that in the cases of the leads coupling to the same-type edges of the dot, the presence of line defect enhances the conductance at the Dirac point by inducing a new conductance peak or strengthening the original conductance peak. Such results are irrelevant to the graphene dot size. On the other hand, if the leads couple to the different-type edges of the dot, the line defect will induce two new conductance peaks near the Dirac point. The conductance enhancement is considered to originate from the fact that one bound state at the Dirac point induced by the line defect couples to the leads, which provides an additional channel for electron motion. Nevertheless, different dot-lead coupling manners change the contribution of the new channel to the electron motion, leading to the complicated transport results. These results show that the line-defect-existed graphene quantum dot will be beneficial to the realization of electron transport manipulation. [ABSTRACT FROM AUTHOR]

We investigate thermal transport through a quantum spin- $1\over2$ heterostructure, in which a semi-infinite chain with two-site isotropic XY interaction couples to the other semiinfinite chain with two-site isotropic XY interaction and three-site XZX+YZY interaction. By studying the dependence of the transmission ability on the model parameters, the linear and nonlinear thermal transport properties are discussed in detail. We find the rectification effects of the heat current in the case of different magnetic fields applied at the two chains; moreover, the unidirectional heat current is observed in the presence of appropriate structure parameters. With these results, we propose such a structure to be a promising candidate for heat current rectification. [ABSTRACT FROM AUTHOR]