Unified numerical approach to topological semiconductor-superconductor heterostructures

Winkler, Georg; Antipov, Andrey E.; Heck, Bernard van; Soluyanov, Alexey A.; Glazman, L. I.; Wimmer, Michael; Lutchyn, Roman M.

doi:10.1103/physrevb.99.245408

Cited by 97 publications

(132 citation statements)

References 90 publications

(173 reference statements)

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“…2(b) and (c). The chosen surface charge values are consistent with experimental estimates for InAs 39 and have been used in previous theoretical studies of Majorana devices 44,45 . As expected, the main effect of the (positive) surface charge is to increase the overall number of occupied subbands.…”

Section: Resultssupporting

confidence: 63%

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Subband occupation in semiconductor-superconductor nanowires

2020

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Subband occupancy (i.e. the number of occupied subbands or energy levels in the semiconductor) is a key physical parameter characterizing the topological properties of superconductor-semiconductor hybrid systems in the context of the search for non-Abelian Majorana zero modes. We theoretically study the subband occupation of semiconductor nanowire devices as function of the applied gate potential, the semiconductor-superconductor (SM-SC) work function difference, and the surface charge density by solving self-consistently the Schrödinger-Poisson equations for the conduction electrons of the semiconductor nanowire. Realistic surface charge densities, which are responsible for band bending, are shown to significantly increase the number of occupied subbands, making it difficult or impossible to reach a regime where only a few subbands are occupied. We also show that the energy separation between subbands is significantly reduced in the regime of many occupied subbands, with highly detrimental consequences for the realization and observation of robust Majorana zero modes. As a consequence, the requirements for the realization of robust topological superconductivity and Majorana zero modes should include a low value of the chemical potential, consistent with the occupation of only a few subbands. Finally, we show that the local density of states on the exposed nanowire facets provides a powerful tool for identifying a regime with many occupied subbands and is capable of providing additional critical information regarding the feasibility of Majorana physics in semiconductor-superconductor devices. In our work, we address both InAs/Al and InSb/Al superconductor-nanowire hybrid systems of current experimental interest.arXiv:1910.04362v1 [cond-mat.mes-hall]

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Section: Resultssupporting

confidence: 63%

“…Following Ref. 44 , we model this surface charge as a uniform layer of (positive) charge of thickness on the nanowire surfaces other than the semiconductor-superconductor interface (see Fig. 1).…”

Section: Device and Modelingmentioning

confidence: 99%

Subband occupation in semiconductor-superconductor nanowires

2020

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“…Recent advances in the modelling of semiconductorsuperconductor hybrid structures have led to more accurate simulations of proximitized nanowires [34,35,46,47]. Here, the essence of our approach is to integrate out the superconductor into self-energy boundary conditions, as discussed in [39].…”

Section: Realistic Simulationsmentioning

confidence: 99%

“…We solve for the electrostatic potential in a separate step using the Thomas-Fermi approximation analog to Ref. [47]. In the semiconductor (InAs) we take m semi = 0.026 m 0 , E F,semi = 0 and g semi = 14.7 [75].…”

Section: Numerical Simulationsmentioning

confidence: 99%

Flux-induced topological superconductivity in full-shell nanowires

Vaitiekėnas

Winkler

Heck

et al. 2020

Science

207

238

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We present a novel route to realizing topological superconductivity using magnetic flux applied to a full superconducting shell surrounding a semiconducting nanowire core. In the destructive Little-Parks regime, reentrant regions of superconductivity are associated with integer number of phase windings in the shell. Tunneling into the core reveals a hard induced gap near zero applied flux, corresponding to zero phase winding, and a gapped region with a discrete zero-energy state around one applied flux quantum, Φ0 = h/2e, corresponding to 2π phase winding. Theoretical analysis indicates that in the presence of radial spin-orbit coupling in the semiconductor, the winding of the superconducting phase can induce a transition to a topological phase supporting Majorana zero modes. Realistic modeling shows a topological phase persisting over a wide range of parameters, and reproduces experimental tunneling conductance data. Further measurements of Coulomb blockade peak spacing around one flux quantum in full-shell nanowire islands shows exponentially decreasing deviation from 1e periodicity with device length, consistent with Majorana modes at the ends of the nanowire. arXiv:2003.13177v1 [cond-mat.mes-hall]

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“…According to the literature (see for instance Ref. 56), the orbital effects are important when the electron's wave function is spread across the wire's section, especially when it has a ringlike shape. In this case, the electrons circulate around the magnetic field that points along the wire and interference orbital effects appear.…”

Section: A Alternative Superlattice Configurationmentioning

confidence: 99%

Effects of the electrostatic environment on superlattice Majorana nanowires

et al. 2019

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Finding ways of creating, measuring and manipulating Majorana bound states (MBSs) in superconducting-semiconducting nanowires is a highly pursued goal in condensed matter physics. It was recently proposed that a periodic covering of the semiconducting nanowire with superconductor fingers would allow both gating and tuning the system into a topological phase while leaving room for a local detection of the MBS wavefunction. We perform a detailed, self-consistent numerical study of a three-dimensional (3D) model for a finite-length nanowire with a superconductor superlattice including the effect of the surrounding electrostatic environment, and taking into account the surface charge created at the semiconductor surface. We consider different experimental scenarios where the superlattice is on top or at the bottom of the nanowire with respect to a back gate. The analysis of the 3D electrostatic profile, the charge density, the low energy spectrum and the formation of MBSs reveals a rich phenomenology that depends on the nanowire parameters as well as on the superlattice dimensions and the external back gate potential. The 3D environment turns out to be essential to correctly capture and understand the phase diagram of the system and the parameter regions where topological superconductivity is established. * Corresponding author: elsa.prada@uam.es 1 M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045

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Unified numerical approach to topological semiconductor-superconductor heterostructures

Cited by 97 publications

References 90 publications

Subband occupation in semiconductor-superconductor nanowires

Subband occupation in semiconductor-superconductor nanowires

Flux-induced topological superconductivity in full-shell nanowires

Effects of the electrostatic environment on superlattice Majorana nanowires

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