InSbAs Two-Dimensional Electron Gases as a Platform for Topological Superconductivity

Abstract

Topological superconductivity can be engineered in semiconductors with strong spin–orbit interaction coupled to a superconductor. Experimental advances in this field have often been triggered by the development of new hybrid material systems. Among these, two-dimensional electron gases (2DEGs) are of particular interest due to their inherent design flexibility and scalability. Here, we discuss results on a 2D platform based on a ternary 2DEG (InSbAs) coupled to in situ grown aluminum. The spin–orbit coupling in these 2DEGs can be tuned with the As concentration, reaching values up to 400 meV Å, thus exceeding typical values measured in its binary constituents. In addition to a large Landé g-factor of ∼55 (comparable to that of InSb), we show that the clean superconductor–semiconductor interface leads to a hard induced superconducting gap. Using this new platform, we demonstrate the basic operation of phase-controllable Josephson junctions, superconducting islands, and quasi-1D systems, prototypical device geometries used to study Majorana zero modes.

Scanning gate microscopy imaging of the supercurrent distribution in a planar Josephson junction

“…Here we theoretically explore the possibility of a direct visualization of the supercurrent distribution and the associated formation of Josephson vortices by a combination of critical current measurements and the scanning gate microscopy (SGM) technique. Our idea exploits the fact that in planar SNS junctions [10][11][12][13][14][15][16][17][18][19][20][21][22] the normal plane between the superconductors remains exposed, which opens the possibility for the application of the SGM technique that has been used successfully for over two decades for imaging of normal current flows. SGM in normal systems is a widely used technique which relies on measuring the conductance when a biased atomic force microscope tip scans over the device, inducing a repulsive potential in the two-dimensional electron gas (2DEG) of the sample and affecting the paths of the propagating electrons.…”

Understanding the Morphological Evolution of InSb Nanoflags Synthesized in Regular Arrays by Chemical Beam Epitaxy

“…Low-dimensional InSb nanostructures have sparked interest in the past few years due to their potential applications in high-speed and low-power electronics [ 1 , 2 ], infrared optoelectronics [ 3 ], spintronics [ 2 , 4 , 5 ], quantum electronics [ 6 , 7 ], and topological quantum computation [ 8 ]. These applications stem from the outstanding intrinsic properties of InSb such as a narrow band gap (≅0.23 eV) [ 4 , 9 , 10 ], high bulk electron mobility (7.7 × 10 4 cm 2 /(V s)) [ 1 , 11 ], small effective mass ( m ∗ = 0.018 m e ) [ 4 , 11 , 12 , 13 , 14 , 15 ], and a large Landé g-factor ( |g ∗ | ∼50, [ 11 , 15 ]). Among the most influential developments are the topological superconducting quantum devices based on InSb nanowires (NWs) [ 16 , 17 ].…”

“…Besides one-dimensional NWs, quasi two-dimensional (quasi-2D) InSb nanostructures, often called nanoflags (NFs), also attract great attention owing to their inherent design flexibility [ 4 , 9 , 15 , 18 ]. InSb NF-based devices have been proven appropriate for studies of novel quantum phenomena, development of scalable topological superconducting devices based on strong spin−orbit coupling [ 19 , 20 , 21 ], and infrared (IR) photodetectors exhibiting a broad spectral detection range [ 22 ].…”

Evidence of Josephson Coupling in a Few-Layer Black Phosphorus Planar Josephson Junction

“…Among all, high-quality two-dimensional electron gases (2DEGs) have been inspected in so-called planar JJs, exploiting peculiar features such as long ballistic transport and conductance quantization in combination with proximity-induced superconducting correlations. 15 − 22 …”