Topological state engineering by potential impurities on chiral superconductors

Abstract

In this work we consider the influence of potential impurities deposited on top of two-dimensional chiral superconductors. As discovered recently, magnetic impurity lattices on an s-wave superconductor may give rise to a rich topological phase diagram. We show that a similar mechanism takes place in chiral superconductors decorated by nonmagnetic impurities, thus avoiding the delicate issue of magnetic ordering of adatoms. We illustrate the method by presenting the theory of potential impurity lattices embedded on chiral p-wave superconductors. While a prerequisite for the topological state engineering is a chiral superconductor, the proposed procedure results in vistas of nontrivial descendant phases with different Chern numbers. DOI: 10.1103/PhysRevB.94.060505 Introduction. Engineering novel quantum phases of matter with exotic properties is a rapidly growing trend in contemporary physics. The main goal is to employ simpler and wellunderstood ingredients and methods to create more complex structures with desirable properties. Recent promising efforts to realize [1][2][3] topological superconductivity in nanowire systems [4,5] demonstrate the power of the approach. While it seems unlikely that Nature directly provides us with Majorana quasiparticles that could be employed in quantum information applications [6], it is increasingly probable that those can be achieved in the laboratory. In the spirit of engineering novel controllable states of matter, we show how to realize a complex hierarchy of topological phases with potential impurity superstructures adsorbed on chiral superconductors. Magnetic atoms on s-wave superconductors give rise to Yu-Shiba-Rusinov subgap states [7][8][9][10] which have been probed experimentally by scanning tunneling microscopy (STM) [11][12][13][14]. Superstructures fabricated from magnetic atoms are currently under active experimental [15][16][17] and theoretical research [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Intriguing properties of these systems include the possibility for various one-dimensional (1D) topological superconducting phases with Majorana bound states and rich two-dimensional (2D) topological phases [34][35][36][37]. A topologically nontrivial phase is known to arise in 1D ferromagnetic arrays when the underlying superconductor has a strong Rasha spin-orbit coupling or in arrays with helical magnetic textures. In 1D structures there are theoretical arguments why magnetic self-tuning could result in a nontrivial ground state [20][21][22]28,32,38], though in real systems there are a number of complications. In particular, in 2D structures the nature and tunability of magnetic textures is a delicate and largely unsolved question.Very recently it was proposed that potential impurities could be utilized to realize interesting topological states in 1D structures [39] and 2D toy models [40]. The procedure requires a non-s-wave superconductor host material with chiral or helical pairing components but circumvents the need for specific magnetic tex...

Bulk boundary correspondence and the existence of Majorana bound states on the edges of 2D topological superconductors

“…This is the result of the well known bulk-boundary correspondence, 16 which relates the topological invariant to the number of topologically protected edge states. Two-dimensional topological superconductors, including for example p-wave or s-wave pairing, have also received a lot of attention, 3,[17][18][19][20][21][22][23][24][25][26][27][28][29][30] and including the model we consider here of a system with spin-orbit coupling, in the presence of superconducting proximity and a Zeeman field, as well as other related models. [31][32][33][34][35][36][37][38][39][40] .…”

Probing chiral edge states in topological superconductors through spin-polarized local density of state measurements

“…Straightforward local density of states (LDOS) measurements cannot easily distinguish between chiral and helical edge states. However, spin-polarization around isolated magnetic impurities have recently been used as a tool to characterize different properties of spin-orbit coupled and topological superconductors [24][25][26][27]. It has also recently been shown that a chiral topological superconductor with Rashba spin-orbit interaction exhibits persistent spin-polarized currents along its edges [28].…”

Localization and oscillations of Majorana fermions in a two-dimensional electron gas coupled with d -wave superconductors

“…Recent experiments confirm the success of the experimental proposal [24,25]. It is also possible to obtain topological superconductivity by depositing magnetic adatoms on top of a conventional s-wave superconductor [26][27][28][29][30][31][32][33], where signatures of Majorana modes have been seen.…”