Electronic properties of InAs/EuS/Al hybrid nanowires

Abstract

We study the electronic properties of InAs/EuS/Al heterostructures as explored in a recent experiment [S. Vaitiekėnas et al., Nat. Phys. 17, 43 (2020)], combining both spectroscopic results and microscopic device simulations. In particular, we use angle-resolved photoemission spectroscopy to investigate the band bending at the InAs/EuS interface. The resulting band offset value serves as an essential input to subsequent microscopic device simulations, allowing us to map the electronic wave function distribution. We conclude that the magnetic proximity effects at the Al/EuS as well as the InAs/EuS interfaces are both essential to achieve topological superconductivity at zero applied magnetic field. Mapping the topological phase diagram as a function of gate voltages and proximity-induced exchange couplings, we show that the ferromagnetic hybrid nanowire with overlapping Al and EuS layers can become a topological superconductor within realistic parameter regimes. Our work highlights the need for a combined experimental and theoretical effort for faithful device simulations.

Optimizing the topological properties of stacking semiconductor-ferromagnet-superconductor heterostructures

“…with ε = 15.5ε 0 being the dielectric constant of InAs. The boundary conditions for the Poisson equation are φ(0) = W ≈ 0.3 V [20] and φ(−d N ) = V g , which are determined jointly by the semiconductor-ferromagnet band offset W at the top and the gate voltage V g at the bottom of the N layer. In reality, there is another thin dielectric layer between the semiconductor and the backgate, leading to a marginal difference in the electrostatic potential simulation inside the semiconductor.…”

“…As pointed out in Refs. [20][21][22][23], the relative positioning of the ferromagnetic and superconducting layers on top of the nanowire could affect the electrostatic potential profile inside the semiconductor as well as the total strength of the induced Zeeman spin splitting in a delicate manner. Additionally, it has also been shown via a phenomenological model that topological superconductivity can appear in a hybrid system when the ferromagnetic film is inserted as a spin-filtering barrier separating the semiconductor and superconductor layers [24,25].…”

Estimating disorder and its adverse effects in semiconductor Majorana nanowires

“…These impurities form a charge accumulation layer that is known to occur on the surfaces of InAs nanowires [99] and are believed to be generated by either ionized hydrogen impurities attaching to the surface or native point defects [100,101]. We note that a surface charge has been included in a few previous theoretical investigations of Majorana nanostructures [102][103][104][105]. However, these studies assumed a uniform surface charge density on the uncovered facets of the device, which yields a translationinvariant potential along the length of the wire.…”

Conductance Spectroscopy of Majorana Zero Modes in Superconductor-Magnetic Insulating Nanowire Hybrid Systems

“…With the aforementioned on one hand, the basic Rashba wire setup has further drawbacks which includes the requirement of large magnetic fields that could potentially destroy superconductivity [37][38][39][40] apart from the practicalities of precise magnetic field alignment [41]. Recently, efforts are being made towards realizing * bm@ee.iitb.ac.in topological superconductivity with zero external magnetic fields by using proximity effects from magnetic insulators (MI) [42][43][44][45][46][47][48][49][50][51][52]. Recent experimental [43] and theoretical works [44][45][46][47][48]51] featuring this setup indicate that at very low external magnetic fields, or even zero external magnetic fields, a topological MZM phase can emerge.…”

“…Recently, efforts are being made towards realizing * bm@ee.iitb.ac.in topological superconductivity with zero external magnetic fields by using proximity effects from magnetic insulators (MI) [42][43][44][45][46][47][48][49][50][51][52]. Recent experimental [43] and theoretical works [44][45][46][47][48]51] featuring this setup indicate that at very low external magnetic fields, or even zero external magnetic fields, a topological MZM phase can emerge. The object of this paper is hence to provide an in-depth analysis of the transport signatures of MZMs in these structures, particularly focusing on the local and non-local conductance spectra in both pristine and disordered nanowires.…”