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 Josephson Effects Mediated by a Dirac Semimetal

Yu, Wenlong; Pan, W.; Medlin, Douglas L.; Rodriguez, Mark A.; Lee, S. R.; Bao, Zhi-qiang; Zhang, Fan

doi:10.1103/physrevlett.120.177704

Cited by 46 publications

(53 citation statements)

References 55 publications

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“…Additional indications of the SC phase in Cd 3 As 2 were also observed in the point-contact spectroscopy experiments and attributed to the local crystal distortions under point-contact [19,20]. It is important to note, that up to now, all indications of the SC phase emergence in Cd 3 As 2 were related either to the pressureinduced structural changes or to the proximity effect with the conventional s-wave SC [21,22].Recent studies of Cd 3 As 2 thin films outlined their specific features. The observation of quantum Hall state [23,24] and consecutive analysis of magnetoresistance of Cd 3 As 2 films suggest the existence of closed Fermi loops (Weyl orbits) related to the surface states, below some critical thickness [25,26].…”

supporting

confidence: 53%

Observation of subkelvin superconductivity in Cd3As2 thin films

et al. 2019

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We report the first experimental observation of superconductivity in Cd3As2 thin films without application of external pressure. Surface studies suggest that the observed transport characteristics are related to the polycrystalline continuous part of investigated films with homogeneous distribution of elements and the Cd-to-As ratio close to stoichiometric Cd3As2. The latter is also supported by Raman spectra of the studied films, which are similar to those of Cd3As2 single crystals. The formation of superconducting phase in films under study is confirmed by the characteristic behavior of temperature and magnetic field dependence of samples resistances, as well as by the presence of pronounced zero-resistance plateaux in dV /dI characteristics. The corresponding Hc−Tc plots reveal a clearly pronounced linear behavior within the intermediate temperature range, similar to that observed for bulk Cd3As2 and Bi2Se3 films under pressure, suggesting the possibility of nontrivial pairing in the films under investigation. We discuss a possible role of sample inhomogeneities and crystal strains in the observed phenomena.Weyl and Dirac semimetals (WSM and DSM) currently attract wide interest related to the existence of Dirac nodes in their electron spectrum and related nontrivial topological characteristics of both bulk and surface states [1][2][3]. A special attention is drawn to the Cd 3 As 2 compound, which proved to be air-stable, unlike some other DSM materials [4][5][6][7][8]. This compound is known and has been studied for quite a long time [9][10][11][12]. Nevertheless, it is still very popular since the Dirac nodes of this semimetal are protected by the crystal symmetry and the electron states exhibit interesting topological properties, such as spin-momentum locking. Due to the high symmetry, DSM materials can undergo transitions to other topological phases (e.g. WSM) as a result of breaking certain symmetries or applying some external factors.The existence of topologically protected electron states gives a new impetus to the problem of topological superconductivity (TSC) being discussed for a long time [13][14][15]. In particular, Refs. [16,17] provide a theoretical analysis of the possible types of SC pairing in the systems of Cd 3 As 2 type, including topologically nontrivial ones. Basically, the existence of nontrivial pairing potential (leading to the emergence of triplet Cooper pairs) should induce the formation of Majoranna modes at the surface of the crystal, which can be used in the faulttolerant quantum computing [14]. The SC phase emergence in Cd 3 As 2 was reported in Ref.[18], however, it was observed at pressures above the structural transition from the tetragonal to trigonal phase. While theoretical works suggest the stabilization of TSC phase upon such symmetry lowering [16,17], such transition also implies appearance of the gap at Dirac nodes, thus, suppressing the DSM phase. Additional indications of the SC phase in Cd 3 As 2 were also observed in the point-contact spectroscopy experiments and att...

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supporting

confidence: 53%

Observation of subkelvin superconductivity in Cd3As2 thin films

et al. 2019

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“…The interference (π periodicity) can appear if both surface and bulk carriers transfer Josephson current in parallel, see Fig. 5, as it has been proposed for Cd 3 As 2 Dirac semimetal 15,16 . This picture gives qualitatively reasonable results: (i) Parallel magnetic field induces a phase shift between surface and bulk channels for Josephson current, which leads to slow I c (B) damping, as we observe in Fig.…”

Section: Discussionmentioning

confidence: 65%

“…Since we can exclude parasite shortings in the junction plane, we should connect the observed multivalued character of the current-phase relationship with non-trivial distribution [10][11][12]15 of the Josephson current within the WTe 2 crystal, i.e., with topological surface states 5,6,8,9 .…”

Section: Discussionmentioning

confidence: 99%

“…In addition to the steps at integer N = 1, 2, 3.., we observe half-integer N = 1/2, 3/2 ones, i.e., π periodicity in a.c. Josephson effect. It usually appears due to interference effects 15,16 , for example, for the double-slit geometries in superconducting quantum interference devices (SQUID) 27,28 . The situation is even more complicated at high power: there are clear-visible N = 1/3, 2/3 steps, which obviously indicates a multivalued nonsinusoidal character of the current-phase relationship 27,28 .…”

Section: B I − V Curves Under Microwave Irradiationmentioning

confidence: 99%

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Subharmonic Shapiro steps in the a.c. Josephson effect for a three-dimensional Weyl semimetal WTe ₂

Shvetsov¹,

Kononov²,

Timonina³

et al. 2018

EPL

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We experimentally study electron transport between two superconducting indium leads, coupled to a single WTe2 crystal, which is a three-dimensional Weyl semimetal. We demonstrate Josephson current in long 5 µm In-WTe2-In junctions, as confirmed by the observation of integer (1,2,3) and fractional (1/3, 1/2, 2/3) Shapiro steps under microwave irradiation. Demonstration of fractional a.c. Josephson effect indicates multivalued character of the current-phase relationship, which we connect with Weyl topological surface states contribution to Josephson current. In contrast to topological insulators and Dirac semimetals, we do not observe 4π periodicity in a.c. Josephson effect for WTe2 at different frequencies and power, which might reflect chiral character of the Fermi arc surface states in Weyl semimetal.

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“…Small (less than 100 µm size) Cd 3 As 2 single crystals are obtained by a mechanical cleaving method, somewhat similar to described in Ref. 39: we crush the initial 5 mm size Cd 3 As 2 single crystal onto small fragments. This procedure allows to create a clean Cd 3 As 2 surface without mechanical polishing or chemical treatment.…”

Section: Samples and Techniquementioning

confidence: 99%

Surface superconductivity in a three-dimensional Cd3As2 semimetal at the interface with a gold contact

et al. 2019

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We experimentally investigate charge transport through a single planar junction between Cd3As2 Dirac semimetal and a normal Au lead. For non-superconducting bulk Cd3As2 samples, we observe non-Ohmic dV /dI(V ) curves, which strongly resemble standard Andreev reflection with well-defined superconducting gap. Andreev-like behavior is demonstrated for Cd3As2 samples with different surface and contact preparation techniques. We connect this behavior with surface superconductivity due to the flat-band formation in Cd3As2, which has been predicted theoretically. The conclusion on superconductivity is also supported by the gap suppression by magnetic fields or temperature.

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π and 4π Josephson Effects Mediated by a Dirac Semimetal

Cited by 46 publications

References 55 publications

Observation of subkelvin superconductivity in Cd3As2 thin films

Observation of subkelvin superconductivity in Cd3As2 thin films

Subharmonic Shapiro steps in the a.c. Josephson effect for a three-dimensional Weyl semimetal WTe ₂

Surface superconductivity in a three-dimensional Cd3As2 semimetal at the interface with a gold contact

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π and 4π Josephson Effects Mediated by a Dirac Semimetal

Cited by 46 publications

References 55 publications

Observation of subkelvin superconductivity in Cd3As2 thin films

Observation of subkelvin superconductivity in Cd3As2 thin films

Subharmonic Shapiro steps in the a.c. Josephson effect for a three-dimensional Weyl semimetal WTe 2

Surface superconductivity in a three-dimensional Cd3As2 semimetal at the interface with a gold contact

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Subharmonic Shapiro steps in the a.c. Josephson effect for a three-dimensional Weyl semimetal WTe ₂