Abstract
Chains of magnetic atoms, placed on the surface of s-wave superconductors, have been established as a laboratory for the study of Majorana bound states. In such systems, the breaking of time reversal due to magnetic moments gives rise to the formation of in-gap states, which hybridize to form one-dimensional topological superconductors. However, in unconventional superconductors even non-magnetic impurities induce in-gap states since scattering of Cooper pairs changes their momentum but not their phase. Here, we propose a path for creating topological superconductivity, which is based on an unconventional superconductor with a chain of non-magnetic adatoms on its surface. The topological phase can be reached by tuning the magnitude and direction of a Zeeman field, such that Majorana zero modes at its boundary can be generated, moved and fused. To demonstrate the feasibility of this platform, we develop a general mapping of films with adatom chains to one-dimensional lattice Hamiltonians. This allows us to study unconventional superconductors such as Sr$_2$RuO$_4$ exhibiting multiple bands and an anisotropic order parameter.
Highlights
Combining topology and superconductivity has been heralded as a new paradigm for the realization of exotic new particles—Majorana zero modes (MZMs)—-whose nonAbelian braiding statistics would enable fault-tolerant quantum computations [1,2]
We can realize unpaired MZMs by breaking the symmetry down to only particle-hole symmetry by use of a Zeeman field such that the system, when tuned into the topological phase, exhibits unpaired MZMs at the end of the impurity chain A Zeeman field in z direction can be described by HeZff,z = heff,zσzτz with a renormalized magnitude heff,z, which can be calculated by including chemical potential shifts ξ (p) ± hz in the bulk dispersion of the spin up and down electrons, respectively
Controllable placing of adatoms might be facilitated by step edges, and in the Supplemental Material [40] we show that the topological phase can be reached by application of a Zeeman field in this case
Summary
Combining topology and superconductivity has been heralded as a new paradigm for the realization of exotic new particles—Majorana zero modes (MZMs)—-whose nonAbelian braiding statistics would enable fault-tolerant quantum computations [1,2]. In the first approach s-wave superconductivity is proximity induced in nanowires with strong spin-orbit coupling [4,5,6,7], while in the second approach the hybridization of impurity (Shiba) bound states gives rise to a topologically nontrivial superconducting phase [8,9,10,11,12,13] The latter has been realized by placing a chain of magnetic atoms on the surface of an s-wave superconductor [14,15,16,17,18]. Implementing our proposal in candidate systems for triplet superconductivity such as UPt3 [34,35], UTe2 [36,37], and LaNiGa2 [38] could establish a new MZM platform and improve the understanding of the pairing symmetries in these systems
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