Influence of topological edge states on the properties of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>Al</mml:mi><mml:mo>/</mml:mo><mml:msub><mml:mo>Bi</mml:mo><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Se</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi>Al</mml:mi></mml:math>hybrid Josephson devices

Galletti, Luca; Charpentier, Sophie; Iavarone, M.; Lucignano, P.; Massarotti, Davide; Arpaia, Riccardo; Suzuki, Yusuke; Kadowaki, K.; Bauch, Thilo; Tagliacozzo, A.; Tafuri, F.; Lombardi, Floriana

doi:10.1103/physrevb.89.134512

Cited by 67 publications

(78 citation statements)

References 84 publications

(115 reference statements)

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“…Typical values for the product of critical current and normal state resistance (I C R N ) are 0.01 -0.2 ∆ Nb /e, see table I in Ref. 17 . The reduction is attributed to an interface barrier between the superconducting electrode and the TI material.…”

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Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

et al. 2016

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We investigate transport and shot noise in lateral N-TI-S contacts, where N is a normal metal, TI is a Bi-based three dimensional topological insulator (3D TI), and S is an s-type superconductor. In the normal state, the devices are in the elastic diffusive transport regime, as demonstrated by a nearly universal value of the shot noise Fano factor FN ≈ 1/3 in magnetic field and in a reference normal metal contact. In the absence of magnetic field, we identify the Andreev reflection (AR) regime, which gives rise to the effective charge doubling in shot noise measurements. Surprisingly, the Fano factor FAR ≈ 0.22 ± 0.02 is considerably reduced in the AR regime compared to FN, in contrast to previous AR experiments in normal metals and semiconductors. We suggest that this effect is related to a finite thermal conduction of the proximized, superconducting TI owing to a residual density of states at low energies.A surface state of a three-dimensional topological insulator (3D TI) is a unique example of a spin-orbit coupled and symmetry protected conductor 1 . Similar to graphene, in 3D TI the surface electronic states are massless Dirac fermions. Unlike in graphene, however, a single Dirac cone is lacking spin and valley degeneracies. That makes a 3D TI an intriguing candidate for the realization of a solid state two-dimensional topological superconductor 2 . As originally proposed by Fu and Kane 3 , p-wave like superconducting correlations are expected to emerge via proximity coupling the 3D TI to a conventional stype superconductor (S). This gives rise to symmetry protected Majorana zero modes bound at vortices or at the boundaries of various hybrid structures 4,5 . Emerging zero modes are predicted to have a strong impact on the low energy physics, modifying Andreev reflection (AR) at the interface with a normal metal 6 , affecting the edge conductance distribution 7 , noise 8 and thermal transport 9,10 .Proximity induced superconductivity has been demonstrated in 3D TIs based on Bi 11-17 and HgTe 18,19 with the reported values of the induced gap on the order of a few 100 µeV. Similar gap values were recently observed via Andreev spectroscopy 20 in quaternary BiSbTeSe compound, established as a 3D TI with negligible contribution of the bulk conduction 21,22 . In spite of these advances, the microscopic nature of the proximity induced gap in Bi-based 3D TIs remains largely unexplored. This particularly concerns the statistics of the transmission eigenvalue distribution in short junctions and the role of possible in-gap states. On this route, valuable information, often hidden in transport, can be obtained via measurements of the non-equilibrium current fluctuationsthe shot noise 23 . Relevant for the AR, prominent examples include unusual shot noise behavior at the interface between a normal metal and superconductors with other than s-type order parameter symmetry 24,25 and, more recently, shot noise detection of the thermal and charge transport via Majorana zero modes 9,10,26 .Here, we investigate the AR in latera...

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Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

et al. 2016

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“…These special properties are reflected in the superconducting proximity effect in an S/3D-TI bilayer or an S/TI/S junction, which may host Majorana fermions in a quasi-1D channel or vortex core [8][9][10]. Most previous works characterized current-voltage characteristics to determine the critical current's dependence on temperature, gate voltage, or magnetic field [11][12][13][14][15][16][17][18][19][20][21][22], while a few studies characterized the CPR [23,24].Here, we use a scanning SQUID microscope to perform contactless measurements of the diamagnetic response of Nb/HgTe bilayers and of the CPR of Nb/HgTe/Nb junctions. In contrast to previous CPR results [23,24], we find no evidence for bulk states, 2 and we observe that the CPRs of many junctions of different sizes consistently exhibit forward skewness.…”

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Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

et al. 2015

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We use Superconducting QUantum Interference Device (SQUID) microscopy to characterize the current-phase relation (CPR) of Josephson Junctions from 3-dimentional topological insulator HgTe (3D-HgTe). We find clear skewness in the CPRs of HgTe junctions ranging in length from 200 nm to 600 nm. The skewness indicates that the Josephson current is predominantly carried by Andreev bound states with high transmittance, and the fact that the skewness persists in junctions that are longer than the mean free path suggests that the effect may be related to the helical nature of the Andreev bound states in the surface of HgTe.Topological insulators (TI) have a special band structure with important consequences for proximity-induced superconductivity. In 3-dimentional topological insulators (3D-TI), the inversion of the conduction and valence bands leads to conducting 2D surface states with energies that are linearly proportional to their momenta [1][2][3][4][5]. Spinmomentum locking protects the charge carriers at the surface against elastic backscattering [6,7]. These special properties are reflected in the superconducting proximity effect in an S/3D-TI bilayer or an S/TI/S junction, which may host Majorana fermions in a quasi-1D channel or vortex core [8][9][10]. Most previous works characterized current-voltage characteristics to determine the critical current's dependence on temperature, gate voltage, or magnetic field [11][12][13][14][15][16][17][18][19][20][21][22], while a few studies characterized the CPR [23,24].Here, we use a scanning SQUID microscope to perform contactless measurements of the diamagnetic response of Nb/HgTe bilayers and of the CPR of Nb/HgTe/Nb junctions. In contrast to previous CPR results [23,24], we find no evidence for bulk states, 2 and we observe that the CPRs of many junctions of different sizes consistently exhibit forward skewness.The CPR in an S/TI/S junction is a key diagnostic [8,[25][26][27][28][29][30][31][32]. Weak disorder in the TI far from the superconducting contacts theoretically does not affect the induced superconducting state [33,34]; therefore, Andreev bound states should form in hightransmittance surface channels [8,26,27,29,31]. A CPR with forward skewness -that is, a deviation from a perfect sinusoidal form -is a signature of such high-transmittance Andreev bound states [35][36][37].To our knowledge, there have not been direct observations of forward skewed CPRs in topological insulators [23,24], although the skewness has been indirectly inferred [24] from the Fraunhofer interference pattern. Previous CPR experiments in topological insulators [23,24] were complicated in part by bulk states, self-inductance effects, and bias voltage, factors that are eliminated in this work.Moreover, a skewed CPR can also result from ballistic transport [35]. Measurements in metallic break junctions showed that the CPR approaches the predictions for quantum point contacts in the ballistic limit [38]. In metallic atomic point contacts, the CPR was significantly skewed only in contacts wi...

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“…1(a) I-V curves of a Al-BiSe (flake) (TI)-Al junction as a function of the temperature clearly indicate an overdamped regime [9], which is retrieved in Fig. 1(c) for a Al-InAs (nanowire)-Al device [14].…”

Section: I-v Curves Of Unconventional Junctionsmentioning

confidence: 99%

“…We report I-V curves of junctions employing two-dimensional barriers as topological insulator flakes (Fig. 1, panels (a) [9] and (b) [10]) or graphene (Fig. 1, panels (e) [11,12] and (f) [13]).…”

Section: Introductionmentioning

confidence: 99%

What happens in Josephson junctions at high critical current densities

Massarotti¹,

Stornaiuolo²,

Lucignano³

et al. 2017

Low Temperature Physics

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The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e. current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities J c . Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-J c junctions. These notions are universal and apply to all kinds of junctions.

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Influence of topological edge states on the properties ofAl/Bi2Se3/Alhybrid Josephson devices

Cited by 67 publications

References 84 publications

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

Andreev Reflection in ans-Type Superconductor Proximized 3D Topological Insulator

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

What happens in Josephson junctions at high critical current densities

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