Giant Fluctuations and Gate Control of the <i>g</i>-Factor in InAs Nanowire Quantum Dots

Csonka, Szabolcs; Hofstetter, L.; Freitag, F.; Oberholzer, S.; Schönenberger, Christian; Jespersen, Thomas Sand; Aagesen, Martin; Nygård, Jesper

doi:10.1021/nl802418w

Cited by 101 publications

(131 citation statements)

References 24 publications

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“…These g factors are higher than the bulk InSb |g| factor of 51. Although spin− orbit interaction is thought to affect |g| factors in confined geometries 37,38 our enhanced |g| factor can likely be attributed to exchange enhancement in low density quantum point contacts. 39−41 A gradual increase of conductance with sourcedrain bias prevents observation of the transition between the 1.0g Q plateau and the 1.25g Q high-bias plateau in transconductance.…”

mentioning

confidence: 82%

Quantized Conductance in an InSb Nanowire

et al. 2012

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Ballistic one-dimensional transport in semiconductor nanowires plays a central role in creating topological and helical states. The hallmark of such one-dimensional transport is conductance quantization. Here we show conductance quantization in InSb nanowires at nonzero magnetic fields. Conductance plateaus are studied as a function of source-drain bias and magnetic field, enabling extraction of the Landég factor and the subband spacing. KEYWORDS:Conductance quantization, ballistic transport, quantum point contact, subband, nanowire, InSb S emiconductor nanowires are the starting point of recently proposed topological systems. 1−3 A topological superconducting region arises in a one-dimensional (1D) semiconductor wire in the presence of a strong spin−orbit coupling when it is brought in contact with a superconducting material. On the boundary of the topological and nontopological wire regions Majorana fermions (MFs) are expected. 4 The MFs in a nanowire, quasi-particles that are an equal superposition of an electron and a hole, are candidate building blocks for faulttolerant quantum computation. 4,5 Moreover, 1D semiconductor wires with strong spin−orbit coupling have also been identified as a suitable platform for creation of a helical state. 6−8 In such a state spin and momentum of an electron are perfectly correlated, thereby creating spin polarization and allowing spin filtering, key themes in the field of spintronics. 9−11 InSb nanowires, alongside InAs and Si/Ge core−shell nanowires, are promising for study of topological and helical states, as they have a strong spin−orbit interaction, 12 and superconductivity can be induced in the nanowires. 13 Indeed signatures of MFs have been reported in hybrid semiconductor−superconductor InSb nanowire devices. 14 While in InSb nanowires the basic properties of spin−orbit interaction and induced superconductivity have each been separately investigated, the degree of fulfillment of the third requirement for creation of MFs, the 1D semiconductor wire, is not as well understood. In a 1D wire transport takes place in subbands, of which the occupation is controlled by an external gate voltage. While first schemes for detection of MFs required occupation of only a single subband near the superconducting contacts where the MFs form, 1,2 later proposals extended this condition to the multisubband regime. 15−17 Information about the energy spectrum of InSb nanowires needed to answer questions of subband occupation is however lacking. Moreover, MFs are affected by disorder in the wire, 17−19 of which the extent is unknown. Such disorder creates diffusive transport, instead of the ballistic transport implied in the 1D requirement. Subband occupation and disorder are also key issues in creation of helical states in InSb nanowires.The formation of subbands in (ballistic) 1D wires is shown in transport measurements by quantization of conductance, where each spin-degenerate subband contributes a conductance of g Q = 2e 2 /h. 20,21 In semiconductor nanowires conductan...

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confidence: 82%

Quantized Conductance in an InSb Nanowire

et al. 2012

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“…17 InSb NWs, in contrast, have higher electron mobility 9,15,18 and, as evidenced by clear demonstrations of quantized conductance, 10,19 less intrinsic disorder than InAs NWs. InSb NWs also have large Lande g factors of ~ 40-50 19 , compared to values of ~5-10 in InAs; [20][21][22] this allows for lower magnetic fields required to induce topological superconductivity. [1][2][3][4] With optimized superconductor-nanowire interfaces, InSb NWs could be potentially a robust platform for observing and controlling 1D topological superconductivity.…”

Section: Mainmentioning

confidence: 99%

Hybrid superconductor-quantum point contact devices using InSb nanowires

Gill

Damasco

Car

et al. 2016

Applied Physics Letters

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Proposals for studying topological superconductivity and Majorana bound states in nanowires proximity coupled to superconductors require that transport in the nanowire is ballistic. Previous work on hybrid nanowire-superconductor systems has shown evidence for Majorana bound states, but these experiments were also marked by disorder, which disrupts ballistic transport. In this letter, we demonstrate ballistic transport in InSb nanowires interfaced directly with superconducting Al by observing quantized conductance at zero-magnetic field. Additionally, we demonstrate that the nanowire is proximity coupled to the superconducting contacts by observing Andreev reflection. These results are important steps for robustly establishing topological superconductivity in InSb nanowires. MainInAs and InSb nanowires (NWs) coupled to superconductors are promising material candidates for studying topological superconductivity harboring Majorana bound states 1,2 and demonstrating non-Abelian particle statistics relevant for topological quantum computation. 3 The basic procedure to observe Majorana zero modes involves tuning a superconducting proximity coupled quantum wire (i.e. a ballistic 1D system) with strong spin-orbit coupling and one spin degenerate mode in magnetic field. 1 Indeed, evidence for Majorana bound states has been observed in proximity-coupled InSb and InAs NWs as a zero-bias conduction peak in tunneling experiments. 4-7 However, preliminary experiments probing Majorana bound states in nanowires were marked by disorder and a soft superconducting gap in the tunneling regime. [4][5][6][7][8] Disorder in nanowire systems is known to break up ballistic transport 9,10 , which is a crucial ingredient for developing 1D topological superconductivity. 1, 2, 4, 9 Additionally, disorder can produce zero-bias conductance signatures similar to Majorana bound states. 11 While the typical signature of ballistic 1D transport-quantized conductance-has been observed in InSb nanowires at high magnetic field 9 and more recently at zero-field, 19 clear demonstrations of ballistic transport at lower fields (< 1T, i.e., before the expected onset of topological superconductivity) in hybrid nanowire-superconductor systems are lacking. Hence, in order to clearly demonstrate topological superconductivity and remove alternative 2 mechanisms for observing zero bias conduction peaks, quantized conductance should be observed at zero magnetic field in NWs proximity coupled to superconductors.Quantized conductance at zero-magnetic field is the step-like increase of conductance with gate voltage through a ballistic 1D constriction, in units of the quantum of conductance, G 0 = 2e 2 /h, for each spin degenerate subband. 12 While quantized conductance in QPCs defined on 2D electron gas (2DEG) materials, such as GaAs heterostructures, is well established, 12-14 demonstrations of quantized conductance in nanowire systems are sparse. In contrast to QPCs in 2DEGs, short nanowire channels contacted by metals are more prone to backscattering ef...

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“…The current distribution for a gate-defined quantum dot in an InAs nanowire [46] is shown in Fig. 17(d).…”

Section: B Disks With Soft Boundariesmentioning

confidence: 99%

Geometric and compositional influences on spin-orbit induced circulating currents in nanostructures

et al. 2014

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Circulating orbital currents, originating from the spin-orbit interaction, are calculated for semiconductor nanostructures in the shape of spheres, disks, spherical shells, and rings for the electron ground state with spin oriented along a symmetry axis. The currents and resulting orbital and spin magnetic moments, which combine to yield the effective electron g factor, are calculated using a recently introduced formalism that allows the relative contributions of different regions of the nanostructure to be identified at zero magnetic field. For all these spherically or cylindrically symmetric hollow or solid nanostructures, independent of material composition and whether the boundary conditions are hard or soft, the dominant orbital current originates from intermixing of valence-band states in the electron ground state, circulates within the nanostructure, and peaks approximately halfway between the center and edge of the nanostructure in the plane perpendicular to the spin orientation. For a specific material composition and confinement character, the confinement energy and orbital moment are determined by a single size-dependent parameter for spherically symmetrical nanostructures, whereas they can be independently tuned for cylindrically symmetric nanostructures.

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Giant Fluctuations and Gate Control of the g-Factor in InAs Nanowire Quantum Dots

Cited by 101 publications

References 24 publications

Quantized Conductance in an InSb Nanowire

Quantized Conductance in an InSb Nanowire

Hybrid superconductor-quantum point contact devices using InSb nanowires

Geometric and compositional influences on spin-orbit induced circulating currents in nanostructures

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