Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures

Wan, Zhong; Kazakov, Alexey S.; Manfra, Michael J.; Pfeiffer, L. N.; West, K. W.; Rokhinson, Leonid P.

doi:10.1038/ncomms8426

Cited by 123 publications

(98 citation statements)

References 42 publications

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“…In our experimental results, we did not observe a zero-bias peak in dV/dI (V) curve therefore we can estimate Z < 0.2 or T > 0.96 for our devices. [6,11] Both the hard gap and SGS are suppressed significantly at temperatures above 400 mK leading to a shift toward zero bias as shown in Figure 3d.…”

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confidence: 91%

“…[11] As shown in Figure 3c, the SGS structures correspond to Δ/2e (cyan dashed line), Δ/3e (light-green dashed line), and gap edge (light-pink dashed line) are observed for junction 3. The shape of the gap and SGS has been shown to be influenced by the ratio of L/ξ N , [6,[11][12][13] where ξ N is the Bardeen-CooperSchrieffer coherence length. The SGS consists of a set of pronounced maxima in dV/dI at V = 2Δ/ne if L/ξ N << 1, but the amplitude of the SGS decreases by increasing the ratio of L/ξ N .…”

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confidence: 99%

“…However, because of the proximity effect a minigap is induced into the 2DEG and the Δ Nb will be replaced with a smaller value Δ ind = 1.76 k B T′ c ≈ 100 µeV which results in ξ N ≈ 2 µm. [6] Therefore we consider the junction with a hard gap to be a short ballistic junction (L/ξ N << 1). Thus the flat dV/dI (V SD ) observed within Δ Nb for four junctions are consistent with BTK theory [11] that predicts such an effect only for junctions with Z < 0.2 where Z is the dimensionless interface barrier strength.…”

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confidence: 99%

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On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions

Delfanazari

Puddy

et al. 2017

Advanced Materials

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A superconducting hard gap in hybrid superconductor–semiconductor devices has been found to be necessary to access topological superconductivity that hosts Majorana modes (non‐Abelian excitation). This requires the formation of homogeneous and barrier‐free interfaces between the superconductor and semiconductor. Here, a new platform is reported for topological superconductivity based on hybrid Nb–In0.75Ga0.25As‐quantum‐well–Nb that results in hard superconducting gap detection in symmetric, planar, and ballistic Josephson junctions. It is shown that with careful etching, sputtered Nb films can make high‐quality and transparent contacts to the In0.75Ga0.25As quantum well, and the differential resistance and critical current measurements of these devices are discussed as a function of temperature and magnetic field. It is demonstrated that proximity‐induced superconductivity in the In0.75Ga0.25As‐quantum‐well 2D electron gas results in the detection of a hard gap in four out of seven junctions on a chip with critical current values of up to 0.2 µA and transmission probabilities of >0.96. The results, together with the large g‐factor and Rashba spin–orbit coupling in In0.75Ga0.25As quantum wells, which indeed can be tuned by the indium composition, suggest that the Nb–In0.75Ga0.25As–Nb system can be an excellent candidate to achieve topological phase and to realize hybrid topological superconducting devices.

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confidence: 91%

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confidence: 99%

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confidence: 99%

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On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions

Delfanazari

Puddy

et al. 2017

Advanced Materials

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“…All of the existing proposals (involving superconductors) require two main ingredients, induced superconductivity via coupling FQH edge state to a superconductor and crossed Andreev tunneling between two edges. The first requirement has already been achieved in experiments [28,29]. However, the second requirement is likely to be difficult to achieve experimentally due to the disruption of FQH edge states placed adjacent to a superconductor.…”

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confidence: 99%

Z3 Parafermionic Zero Modes without Andreev Backscattering from the 2/3 Fractional Quantum Hall State

Alavirad¹,

Clarke²,

Nag³

et al. 2017

Phys. Rev. Lett.

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Parafermionic zero modes are a novel set of excitations displaying non-Abelian statistics somewhat richer than that of Majorana modes. These modes are predicted to occur when nearby fractional quantum Hall edge states are gapped by an interposed superconductor. Despite substantial experimental progress, we argue that the necessary crossed Andreev reflection in this arrangement is a challenging milestone to reach. We propose a superconducting quantum dot array structure on a fractional quantum Hall edge that can lead to parafermionic zero modes from coherent superconducting forward scattering on a quantum Hall edge. Such coherent forward scattering has already been demonstrated in recent experiments. We show that for a spin-singlet superconductor interacting with loops of spin unpolarized 2/3 fractional quantum edge, even an array size of order ten should allow one to systematically tune into a parafermionic degeneracy.Introduction.-Theoretical understanding and experimental realization of non-Abelian anyons has attracted considerable attention in the past few years. This surge of interest can be largely attributed to potential application of such systems as building blocks for topological quantum computers [1]. Majorana zero modes (MZMs) [2][3][4][5][6][7] provide the simplest and experimentally the most promising example of non-Abelian anyons. So far, most of the effort in searching for non-Abelian anyons has been focused on MZMs. Following a series of theoretical proposals [8][9][10][11], suggestive experimental evidence of MZMs has been observed in semiconductor/superconductor heterostructures [12][13][14][15][16][17][18]. Despite their fascinating properties MZMs are non-Abelian anyons of the Ising (Z 2 ) type. Universal quantum computation cannot be implemented using braiding of the Z 2 anyons alone. Therefore, searching for a computationally richer set of anyons seems necessary.

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“…Twisted bilayer graphene is also a possible candidate, as it has been shown to realize an integer QSH state [43,44]. Recent experiments have demonstrated advances in coupling superconductors to semiconductor 2DEGS [45,46], e.g. through epitaxial growth [46] and to graphene in the quantum Hall regime [47].…”

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confidence: 99%

Charge2e/3Superconductivity and Topological Degeneracies without Localized Zero Modes in Bilayer Fractional Quantum Hall States

Barkeshli

2016

Phys. Rev. Lett.

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It has been recently shown that non-Abelian defects with localized parafermion zero modes can arise in conventional Abelian fractional quantum Hall (FQH) states. Here we propose an alternate route to creating, manipulating, and measuring topologically protected degeneracies in bilayer FQH states coupled to superconductors, without the creation of localized parafermion zero modes. We focus mainly on electron-hole bilayers, with a ±1/3 Laughlin FQH state in each layer, with boundaries that are proximity-coupled to a superconductor. We show that the superconductor induces charge 2e/3 quasiparticle-pair condensation at each boundary of the FQH state, and that this leads to (1) topologically protected degeneracies that can be measured through charge sensing experiments and (2) a fractional charge 2e/3 AC Josephson effect. We demonstrate that an analog of non-Abelian braiding is possible, despite the absence of a localized zero mode. We discuss several practical advantages of this proposal over previous work, and also extensions to electron-electron bilayers at ν = 2/3 + 1/3 coupled to superconductivity, and to electron-hole bilayers with only interlayer tunneling.A profound feature of topologically ordered states of matter is the existence of topologically protected degeneracies [1]. These are degeneracies in the ground state spectrum of a given Hamiltonian for which no local operator can distinguish the topologically distinct states, thus rendering them robust to local perturbations. Topological degeneracies are predicted to occur when a topological phase is defined on a space with nontrivial topology, such as a torus [2,3], when the system hosts non-Abelian quasiparticle excitations [4][5][6][7], and in topological superconductors when Majorana zero modes are bound to cores of vortices or the ends of one-dimensional wires [8][9][10][11][12][13][14][15].It has recently been shown theoretically that a wide class of non-Abelian defects can be realized in conventional Abelian fractional quantum Hall (FQH) states, such as the Laughlin FQH states, by suitably controlling the tunneling processes along the edge modes. In particular, it was shown that in bilayer FQH states, domain walls between regions of interlayer and intra-layer tunneling can give rise to a novel type of non-Abelian defect that generalizes Majorana zero modes by yielding m states per pair of defects, where the integer m depends on the filling fraction ν of the FQH state [16]. These non-Abelian defects were subsequently shown to also arise as lattice defects in certain lattice spin models [17], extending [18]. They were then also shown to arise in FQH systems coupled to superconductors, at domain walls between regions of normal and Andreev backscattering at the edge [19][20][21], where they were referred to as parafermion [22], or fractionalized Majorana, zero modes. The general theory of these defects [23][24][25][26][27], a number of experimental proposals in FQH systems [28][29][30], other exotic phenomena at the boundary of FQH states and superconduct...

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Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures

Cited by 123 publications

References 42 publications

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions

Z3 Parafermionic Zero Modes without Andreev Backscattering from the 2/3 Fractional Quantum Hall State

Charge2e/3Superconductivity and Topological Degeneracies without Localized Zero Modes in Bilayer Fractional Quantum Hall States

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Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures

Cited by 123 publications

References 42 publications

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In0.75Ga0.25As‐Quantum‐Well–Nb Josephson Junctions

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In0.75Ga0.25As‐Quantum‐Well–Nb Josephson Junctions

Z3 Parafermionic Zero Modes without Andreev Backscattering from the 2/3 Fractional Quantum Hall State

Charge2e/3Superconductivity and Topological Degeneracies without Localized Zero Modes in Bilayer Fractional Quantum Hall States

Contact Info

Product

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On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions

On‐Chip Andreev Devices: Hard Superconducting Gap and Quantum Transport in Ballistic Nb–In_0.75Ga_0.25As‐Quantum‐Well–Nb Josephson Junctions