Search

We study the Kondo screening of a magnetic impurity in a two-dimensional superconductor with Rashba spin-orbit coupling (SOC). It is found that the Rashba interaction generates a novel Kondo screening channel, in which the local moment is screened by the exchange coupling with conduction electrons in different spin and orbital states. The Kondo temperature associated with this process is determined by the interplay between the Rashba SOC and superconducting energy gap. As a result, the quantum phase transition between the magnetic doublet and Kondo singlet ground states is significantly affected by increasing Rashba SOC in such a system. This result uncovers that the Rashba SOC plays an instructive role and provides a novel screening channel for the Kondo effect, which is expected to be observed in future experiments., Comment: 8 pages, 3 figures

Graphene nanoribbons with armchair edges are studied for externally enhanced, but realistic parameter values: enhanced Rashba spin-orbit coupling due to proximity to a transition metal dichalcogenide like WS$_{2}$, and enhanced Zeeman field due to exchange coupling with a magnetic insulator like EuS under applied magnetic field. The presence of s--wave superconductivity, induced either by proximity or by decoration with alkali metal atoms like Ca or Li, leads to a topological superconducting phase with Majorana end modes. The topological phase is highly sensitive to the application of uniaxial strain, with a transition to the trivial state above a critical strain well below $0.1\%$. This sensitivity allows for real space manipulation of Majorana fermions by applying non-uniform strain profiles. Similar manipulation is also possible by applying inhomogeneous Zeeman field or chemical potential., Comment: 5 pages, 5 figures; references added

We present a detailed analysis on the hopping between monolayer CuO$_2$ and bulk CuO$_2$ plane in the Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ substrate. With a two-band model, we demonstrate that the nodeless gap can only exist when the hole concentration in monolayer CuO$_2$ plane is very large or very small. We argued that the possible phase separation may play important role in the recent experimental observation of nodeless gap., Comment: 5 pages, 5 figures

The functionalized graphene with induced superconductivity, Zeeman coupling, and finite Rashba spin-orbit coupling is proposed to display topological superconducting phases with Majorana end modes. We obtain the phase diagram of bulk graphene and nanoribbon by calculating the Chern number, band structure and wavefunction. The electron doping in graphene, magnetic field and strain-induced pseudomagnetic field can result in the topological phase transition. Moreover, it is interested to note that strain has negative influence on the stability of topological nontrivial phase either uniform or nonuniform, destroying the existence of Majorana fermion, which provides a new way to transfer, create and fuse Majorana fermions. Some experimental schemes are also introduced to tailor functionalized graphene, generating various devices applied in topological quantum computation.

Majorana fermions in some model semiconductor nanowires proximity coupled with \emph{s}-wave superconductor have been investigated, as well as other intragap bound states in topological phase of a Rashba nanowire with non-uniform spin-orbit interaction (SOI). Various sources of disorder, such as disorder in semiconductor nanowire, bulk superconductor and semiconductor-superconductor interface, are included to characterize their effects on the stability of the topological phase. In the case of multiband semiconducting nanowires, the phase diagram of the system as a function of the chemical potential and magnetic field have been calculated. In two-band wire or two coupled single band wire, the phase of one band can be controlled through the other band, and these properties is critical to build multiband quantum device. When the SOI vector or magnetic field in semiconductor nanowire rapidly rotates by the angle $\pi $, changes its sign, a topological $\pi $ junction forms at the junction between two wire sections characterized by different directions of the SOI vectors or magnetic field. In this case, some fermionic bound states (FBS) can emerge inside the proximity gap, which localize at the topological $\pi $ junction, and coexist with Majorana bound states localized at the nanowire ends. Changing the position of the topological $\pi $ junction from one end to the other, the zero-energy FBS moves and can be used as mediator to transfer quantum information between two distance MFs. Meanwhile, the Andreev spectrum of the junction is qualitatively phase shift by $\pi $ compared to usual Majorana weak links. The FBS can act as quasiparticle traps and serve as an effective mediator of hybridization between two distant Majorana bound states (MBSs)., Comment: text overlap with arXiv:1408.3366, arXiv:1106.3078 by other authors