Advantages of using high-temperature cuprate superconductor heterostructures in the search for Majorana fermions

Abstract

We propose an alternative platform to observe Majorana bound states in solid state systems. High critical temperature cuprate superconductors can induce superconductivity, by proximity effect, in quasi one dimensional nanowires with strong spin orbit coupling. They favor a wider and more robust range of conditions to stabilize Majorana fermions due to the large gap values, and offer novel functionalities in the design of the experiments determined by different dispersion for Andreev bound states as a function of the phase difference.Recently there is an increasing interest in topological quantum computation based on Majorana Bound States (MBS's) [1,2]. Majorana Fermions have been predicted in a wide class of low-dimensional solid state devices. Many of these proposals make use of quasi one dimensional superconductors in contact with topological insulators [3] or quasi one-dimensional materials with strong spin orbit interactions [4][5][6][7]. Also helical magnets [8] and other materials [9][10][11][12][13] are considered. In this paper we propose a quite distinctive heterostructure to observe topologically protected MBS's in a solid state device. Our work rests on the physics of S/R/S hybrid structures in which "R" is a quasi one dimensional semiconductor nanowire (NW) with strong Rashba spin orbit coupling (e.g. InAs or InSb) electrically connected to two conventional low T c superconductor leads ( "S" ) [4,5]. Superconductivity is induced in the spin-orbit coupled semiconductor by proximity effect due to the superconducting electrodes. The coexistence of superconductivity and spin-orbit coupling is a key ingredient for the existence of MBS's at the interfaces between the R region and the superconducting S regions.However, despite the considerable theoretical and experimental [14] efforts, some challenges still remain before a real device allowing isolation and manipulation of MBS's in such geometry can be realized. In particular the difficulties of tuning the chemical potential of the semiconductor region µ, controlling the disorder on the bulk gap as well as optimizing the coupling between the different materials [15][16][17] make the realization of such devices extremely difficult.All schemes proposed up to now to generate MBS's substantially use conventional s-wave superconductors to induce superconductivity and a gap ∆ in the R nanowire [1]. The role of superconducting pairing is to relax number conservation, thus allowing for the mixing of particle and hole degrees of freedom. Zeeman spin splitting is required to halve the number of degrees of freedom at low energies, thus generating the elusive neutral (Majorana) excitation. A simple criterion to induce MBS's at S/R interfaces is given in terms of the applied magnetic field B x oriented along the wire, µ and ∆. The inequality to be satisfied can be stated as:. Low critical magnetic fields (H c ) and low gap values characteristic of conventional low Tc superconductors substantially define the limits of the nominal range of dynamical parameters required to...

Suspended InAs nanowire Josephson junctions assembled via dielectrophoresis

“…In particular it could be combined with HTS layers which require rather extreme growth conditions. The fabrication of HTS---NW Josephson junctions could be relevant to the observation of Majorana excitations in hybrid systems 24 , allow higher operation temperatures and a more robust behavior in external magnetic fields. Fig.1.…”

“…We also show that the properties of the hybrid devices realized using this method are comparable with those of conventional non---suspended devices. We believe that our DEP technique is suitable for the fabrication of a wide class of hybrid NW---based devices which can include, for instance, High critical Temperature Superconductors (HTS) 24 . The relevance of our protocol for the implementation of field---effect HTS hybrid devices will be discussed.…”

Macroscopic quantum tunneling and retrapping processes in moderately damped YBaCuO Josephson junctions

“…The diffusive regime appears to be of higher importance with the advent of JJs of very reduced size which are becoming to be highly utilized in superconducting hybrid nanoscale devices [5,6,36,37]. This experiments contributes to settle an unexplored region of the phase diagram which is a valid guideline in order to define the relation between the fundamental junction parameters and energies in moderately damped systems.…”

Topological rf SQUID with a frustratingπjunction for probing the Majorana bound state

“…28 , π junctions can display a MBS at a phase difference ϕ = 0, rather than ϕ = π. Here a corresponding state is found in the ring geometry, stabilized with respect to residual interactions.…”