Tunneling Spectroscopy of Quasiparticle Bound States in a Spinful Josephson Junction

Chang, Won; Manucharyan, Vladimir; Jespersen, Thomas Sand; Nygård, Jesper; Marcus, C. M.

doi:10.1103/physrevlett.110.217005

Cited by 187 publications

(212 citation statements)

References 50 publications

Supporting

Mentioning

192

Contrasting

Order By: Relevance

“…A weakly coupled tunnel probe (Au) at bias voltage V measures the excitation spectrum of electron and hole quasiparticles confined to the quantum dot, as a function of the phase difference φ = Φ × 2e/ across the junction. Electron micrographs (entire device and enlarged region) from Chang et al (2013).…”

Section: B Superconducting Quasiparticlesmentioning

confidence: 99%

Random-matrix theory of Majorana fermions and topological superconductors

2015

View full text Add to dashboard Cite

The theory of random matrices originated half a century ago as a universal description of the spectral statistics of atoms and nuclei, dependent only on the presence or absence of fundamental symmetries. Applications to quantum dots (artificial atoms) followed, stimulated by developments in the field of quantum chaos, as well as applications to Andreev billiards -quantum dots with induced superconductivity. Superconductors with topologically protected subgap states, Majorana zero-modes and Majorana edge modes, provide a new arena for applications of random-matrix theory. We review these recent developments, with an emphasis on electrical and thermal transport properties that can probe the Majorana fermions.

show abstract

Section: B Superconducting Quasiparticlesmentioning

confidence: 99%

Random-matrix theory of Majorana fermions and topological superconductors

2015

View full text Add to dashboard Cite

show abstract

“…The relevant experimental quantity is the tunneling differential conductance G (V) at an end of the NW, which is related to the local density of states [24][25][26]28]. We calculate G (V) using the tunneling formalism by coupling the NW to a contact lead [21,22,42].…”

Section: ⊥Imentioning

confidence: 99%

“…For a semiconductor nanowire (NW), it was predicted that the presence of MBS at its ends could be experimentally detected in the differential tunneling conductance G(V) at the interface with a normal contact, via the emergence of a zero-bias peak (ZBP) of height 2e 2 /h (at zero temperature) [19][20][21][22][23]. The NW proposal has inspired a number of recent experiments in which suggestive ZBPs have been observed [24][25][26][27][28]. However, whether these ZBPs are truly due to Majorana zero modes is still uncertain.…”

mentioning

confidence: 99%

Soft Superconducting Gap in Semiconductor Majorana Nanowires

et al. 2013

View full text Add to dashboard Cite

We theoretically consider the ubiquitous soft gap measured in the tunneling conductance of semiconductorsuperconductor hybrid structures, in which recently observed signatures of elusive Majorana bound states have created much excitement. We systematically study the effects of magnetic and non-magnetic disorder, temperature, dissipative Cooper pair breaking, and interface inhomogeneity, which could lead to a soft gap. We find that interface inhomogeneity with moderate dissipation is the only viable mechanism that is consistent with the experimental observations. Our work indicates that improving the quality of the superconductor-semiconductor interface should result in a harder induced gap.

show abstract

“…Although the superconducting proximity effect in graphene has attracted considerable research interest [19][20][21][22][23][24][25][26][27][28][29] , most of the experimental studies have been limited to transport measurements of dissipationless supercurrent in graphene-based (S-G-S) Josephson junctions. Accessing the energy domain while controlling the superconducting phase difference is crucial for probing ABS, and it has been performed in just a few systems, such as silver wires 9 , carbon nanotubes 10 , semiconductor nanowires 11 , and atomic breakjunctions 12,13 . However, a direct spectroscopic observation of phasedependent ABS in graphene is missing.…”

mentioning

confidence: 99%

“…This proximity e ect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states [3][4][5][6][7][8] . Spectroscopic studies of Andreev states have been performed in just a handful of systems [9][10][11][12][13] . The unique geometry, electronic structure and high mobility of graphene 14,15 make it a novel platform for studying Andreev physics in two dimensions.…”

mentioning

confidence: 99%

Tunnelling spectroscopy of Andreev states in graphene

et al. 2017

View full text Add to dashboard Cite

A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties 1,2 . This proximity e ect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states [3][4][5][6][7][8] . Spectroscopic studies of Andreev states have been performed in just a handful of systems 9-13 . The unique geometry, electronic structure and high mobility of graphene 14,15 make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity e ect in superconductor-graphenesuperconductor junctions. The measured energy spectra, which depend on the phase di erence between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between di erent mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson e ect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials [16][17][18] .When a normal quantum conductor (N) is sandwiched between two superconductors (S), a current can flow in the absence of any voltage, due to the Josephson effect 1 . This macroscopic supercurrent is driven by the difference between the order parameter phases of the two superconductors, ϕ. Microscopically, it corresponds to the coherent flow of Cooper pairs through the conductor, which is made possible by successive Andreev reflections at the N/S interfaces, where electrons (holes) are reflected as oppositespin holes (electrons) (Fig. 1a). Due to this process, resonant electron-hole states form in the central conductor, known as Andreev bound states (ABS) 3-6 . They lie as energy levels inside the superconducting gap [−∆, ∆], only negative-energy states being populated in the ground state (Fig. 1b). Crucially, the Andreev energy E n (ϕ) depends on ϕ, and each populated ABS carries in response a supercurrent (1/φ 0 )(∂E n /∂ϕ), where φ 0 = /2e is the reduced flux quantum, with the reduced Planck constant and e the elementary charge. The overall phase-dependent Andreev spectrum is shown in Fig. 1c and depends on geometric and microscopic parameters 7,8 , such as the conductor dimensions that determine the number of ABS, the scattering processes in the conductor and the contact's transparency. Strong ABS phase dependence, and therefore a prominent proximity effect, is achieved in ballistic systems with transparent N/S interfaces 7,8 .Graphene (G) can exhibit low contact resistance and weak scattering when connected to superconducting electrodes 19,20 . These properties, combined with t...

show abstract

Tunneling Spectroscopy of Quasiparticle Bound States in a Spinful Josephson Junction

Cited by 187 publications

References 50 publications

Random-matrix theory of Majorana fermions and topological superconductors

Random-matrix theory of Majorana fermions and topological superconductors

Soft Superconducting Gap in Semiconductor Majorana Nanowires

Tunnelling spectroscopy of Andreev states in graphene

Contact Info

Product

Resources

About