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Register a new userProximity-induced gap in nanowires with a thin superconducting shell
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Coupling a normal metal wire to a superconductor induces an excitation gap in the normal metal. In the absence of disorder, the induced excitation gap is strongly suppressed by finite-size effects if the thickness of the superconductor is much smaller than the thickness of the normal metal and the superconducting coherence length. We show that the presence of disorder, either in the bulk or at the exposed surface of the superconductor, significantly enhances the magnitude of the induced gap, such that it approaches the superconducting gap in the limit of strong disorder. We also discuss the shift of energy bands inside the normal-metal wire as a result of the coupling to the superconducting shell.
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We propose a way of making graphene superconductive by putting on it small superconductive islands which cover a tiny fraction of graphene area. We show that the critical temperature, T_c, can reach several Kelvins at the experimentally accessible range of parameters. At low temperatures, T<<T_c, and zero magnetic field, the density of states is characterized by a small gap E_g<T_c resulting from the collective proximity effect. Transverse magnetic field H_g(T) E_g is expected to destroy the spectral gap driving graphene layer to a kind of a superconductive glass state. Melting of the glass state into a metal occurs at a higher field H_{g2}(T).
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The proximity effect (PE) between superconductor and confined electrons can induce the effective pairing phenomena of electrons in nanowire or quantum dot (QD). Through interpreting the PE as an exchange of virtually quasi-excitation in a largely gapped superconductor, we found that there exists another induced dynamic process. Unlike the effective pairing that mixes the QD electron states coherently, this extra process leads to dephasing of the QD. In a case study, the dephasing time is inversely proportional to the Coulomb interaction strength between two electrons in the QD. Further theoretical investigations imply that this dephasing effect can decrease the quality of the zero temperature mesoscopic electron transportation measurements by lowering and broadening the corresponding differential conductance peaks.
Topological superconductivity is a state of matter that can host Majorana modes, the building blocks of a topological quantum computer. Many experimental platforms predicted to show such a topological state rely on proximity-induced superconductivity. However, accessing the topological properties requires an induced hard superconducting gap, which is challenging to achieve for most material systems. We have systematically studied how the interface between an InSb semiconductor nanowire and a NbTiN superconductor affects the induced superconducting properties. Step by step, we improve the homogeneity of the interface while ensuring a barrier-free electrical contact to the superconductor, and obtain a hard gap in the InSb nanowire. The magnetic field stability of NbTiN allows the InSb nanowire to maintain a hard gap and a supercurrent in the presence of magnetic fields (~ 0.5 Tesla), a requirement for topological superconductivity in one-dimensional systems. Our study provides a guideline to induce superconductivity in various experimental platforms such as semiconductor nanowires, two dimensional electron gases and topological insulators, and holds relevance for topological superconductivity and quantum computation.
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