Hard Superconducting Gap in InSb Nanowires

Gül, Önder; Zhang, Hao; Vries, Folkert K. de; Veen, Jasper van; Zuo, Kun; Mourik, Vincent; Conesa‐Boj, Sonia; Nowak, M. P.; Woerkom, David J. van; Quintero‐Pérez, Marina; Cassidy, Maja; Geresdi, Attila; Koelling, Sebastian; Car, Diana; Plissard, Sébastien; Bakkers, Erik P. A. M.; Kouwenhoven, Leo P.

doi:10.1021/acs.nanolett.7b00540

Cited by 131 publications

(140 citation statements)

References 83 publications

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“…Because of this, we cannot directly compare the current suppression in our device (which has two superconducting contacts) with other work probing the induced gap using a single superconducting contact. Nevertheless, the high ⟨G G ⟩/⟨G O ⟩ ratio suggests that our semiconductornanowire interface homogeneity is comparable to InAs nanowire devices using epitaxial growth techniques [18] or specialized surface treatments [21].…”

Section: Hard Superconducting Gapmentioning

confidence: 93%

“…In the second part, we map the switching current I SW as a function of critical field B C and critical temperature T C of device A and B, which clearly shows an additional superconducting phase in both devices. In the final part we investigate the hardness of the superconducting gap in- duced in the semiconducting nanowire of device A, by means of electronic transport measurements near depletion [18,21] and observe that the conductance in the gap is suppressed by a factor ∼ 1000.…”

Section: Introductionmentioning

confidence: 99%

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Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge–Si Nanowires

et al. 2019

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We show a hard induced superconducting gap in a Ge-Si nanowire Josephson transistor up to in-plane magnetic fields of 250 mT, an important step towards creating and detecting Majorana zero modes in this system. A hard induced gap requires a highly homogeneous tunneling heterointerface between the superconducting contacts and the semiconducting nanowire. This is realized by annealing devices at 180• C during which aluminium inter-diffuses and replaces the germanium in a section of the nanowire. Next to Al, we find a superconductor with lower critical temperature (T C = 0.9 K) and a higher critical field (B C = 0.9 − 1.2 T). We can therefore selectively switch either superconductor to the normal state by tuning the temperature and the magnetic field and observe that the additional superconductor induces a proximity supercurrent in the semiconducting part of the nanowire even when the Al is in the normal state. In another device where the diffusion of Al rendered the nanowire completely metallic, a superconductor with a much higher critical temperature (T C = 2.9 K) and critical field (B C = 3.4 T) is found. The small size of diffusion-induced superconductors inside nanowires may be of special interest for applications requiring high magnetic fields in arbitrary direction. arXiv:1907.05510v2 [cond-mat.mes-hall]

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Section: Hard Superconducting Gapmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge–Si Nanowires

et al. 2019

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“…Since then, significant progress has been made in Majorana experiments [11][12][13][14], enabled by more uniform coupling between the superconductor and semiconductor nanowire. This has been achieved by improved interface engineering: through careful ex situ processing [15][16][17], by depositing the superconductor on the nanowires in situ [18,19], and a combination of in situ and ex situ techniques [20], finally leading to the quantization of the Majorana conductance [13].…”

Section: Introductionmentioning

confidence: 99%

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

et al. 2018

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We study the effect of external electric fields on superconductor-semiconductor coupling by measuring the electron transport in InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor. We find that the gate voltage induced electric fields can greatly modify the coupling strength, which has consequences for the proximity induced superconducting gap, effective g-factor, and spin-orbit coupling, which all play a key role in understanding Majorana physics. We further show that level repulsion due to spin-orbit coupling in a finite size system can lead to seemingly stable zero bias conductance peaks, which mimic the behavior of Majorana zero modes. Our results improve the understanding of realistic Majorana nanowire systems. gate induced electric fields. Due to the change in coupling, the renormalization of material parameters is altered, as evidenced by a change in the effective g-factor of the hybrid system. Furthermore, the electric field is shown to affect the spin-orbit interaction, revealed by a change in the level repulsion between Andreev states. Our experimental findings are corroborated by numerical simulations. Experimental set-upWe have performed tunneling spectroscopy experiments on four InSb-Al hybrid nanowire devices, labeled A-D, all showing consistent behavior. The nanowire growth procedure is described in [20]. A scanning electron micrograph (SEM) of device A is shown in figure 1(a). Figure 1(b) shows a schematic of this device and the measurement set-up. For clarity, the wrap-around tunnel gate, tunnel gate dielectric and contacts have been removed on one side. A normal-superconductor (NS) junction is formed between the part of the nanowire covered by a thin shell of aluminum (10 nm thick, indicated in green, S), and the Cr /Au contact (yellow, N). The transmission of the junction is controlled by applying a voltage V Tunnel to the tunnel gate (red), galvanically isolated from the nanowire by 35 nm of sputtered SiN x dielectric. The electric field is induced by a global back gate voltage V BG , except in the case of device B, where this role is played by the side gate voltage V SG . Further details on device fabrication and design are included in appendices A and B. To obtain information about the density of states (DOS) in the proximitized nanowire, we measure the differential conductance dI/dV Bias as a function of applied bias voltage V Bias . In the following, we will label this quantity as dI/dV for brevity. A magnetic field is applied along the nanowire direction (x-axis in figures 1(b), (c)). All measurements are performed in a dilution refrigerator with a base temperature of 20 mK. Theoretical modelThe device geometry used in the simulation is shown in figure 1(c). We consider a nanowire oriented along the x-direction, with a hexagonal cross-section in the yz-plane. The hybrid superconductor-nanowire system is described by the Bogoliubov-de Gennes (BdG) Hamiltonian

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“…For example, InSb is utilized nowadays in infrared detectors and is very potential for high-speed transistors operating at low voltages 1–6 and other ultra thin device applications 7,8 , and very recently, e.g., as building blocks of quantum computers 9 and THz transport waveguides 10 . The common challenge in developing these various InSb-based devices is how the surface or interface properties of InSb crystals can be modified in controlled manner.…”

Section: Introductionmentioning

confidence: 99%

“…This is the same method we have used previously for preparing crystalline oxidized III–V(100) surfaces 14 , found to reduce the amount of defect states by over an order of magnitude beneath an atomic layer deposition (ALD) grown oxide film 15 and thus enabling efficient passivation. However, the following crucial questions have previously remained unresolved: (i) is the crystalline oxidation possible for other crystal planes; in more general for various crystal faces [not only (100) planes] exposed in nanotechnology 2,7–9,12,16,17 , and (ii) how to produce clean InSb surfaces in an industrially potential way, which is necessary in order to perform the crystalline pre-oxidation in practice. Here we provide solutions to these questions using InSb(111)B as a template for investigations.…”

Section: Introductionmentioning

confidence: 99%

Crystalline and oxide phases revealed and formed on InSb(111)B

Mäkelä

Rad

Lehtiö

et al. 2018

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Oxidation treatment creating a well-ordered crystalline structure has been shown to provide a major improvement for III–V semiconductor/oxide interfaces in electronics. We present this treatment’s effects on InSb(111)B surface and its electronic properties with scanning tunneling microscopy and spectroscopy. Possibility to oxidize (111)B surface with parameters similar to the ones used for (100) surface is found, indicating a generality of the crystalline oxidation among different crystal planes, crucial for utilization in nanotechnology. The outcome is strongly dependent on surface conditions and remarkably, the (111) plane can oxidize without changes in surface lattice symmetry, or alternatively, resulting in a complex, semicommensurate quasicrystal-like structure. The findings are of major significance for passivation via oxide termination for nano-structured III–V/oxide devices containing several crystal plane surfaces. As a proof-of-principle, we present a procedure where InSb(111)B surface is cleaned by simple HCl-etching, transferred via air, and post-annealed and oxidized in ultrahigh vacuum.

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Hard Superconducting Gap in InSb Nanowires

Cited by 131 publications

References 83 publications

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge–Si Nanowires

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge–Si Nanowires

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

Crystalline and oxide phases revealed and formed on InSb(111)B

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