Observation of subkelvin superconductivity in Cd3As2 thin films

Abstract

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...

Superconductivity and Shubnikov - de Haas effect in polycrystalline Cd3As2 thin films

“…The energy-dispersive X-ray (EDX) spectroscopy results demonstrated that the Cd and As distributed homogeneously within the film, while the actual elemental composition is close to the stoichiometric Cd 3 As 2 within 2% accuracy (corresponding results include both averaging over large surface areas and analysis in points with different contrast). Described SEM results are very close to those reported earlier for magnetron-sputtered f ilms 20 . The crystal structure of studied films were investigated using X-ray diffraction (XRD) measurements (see Fig.…”

“…However, one can distinguish three pronounced peaks (marked by green circles in Fig. 1b 20 , we argued that the polycrystalline nature of samples was partially related to the presence of both α and α′ phases. Corresponding XRD patterns also indicated partial orientation of Cd 3 As 2 crystallites with the average size of about 35 nm.…”

Interfacial Superconductivity on the Topological Semimetal Tungsten Carbide Induced by Metal Deposition

“…This characteristic is similar to that of the interfacial superconductivity previously reported in SrTiO 3 /LaAlO 3 system [ 33 ] and that of the superconducting Cd 3 As 2 film. [ 34 ] The critical current was determined to be about 0.9 milliampere. Figure 1e presents a series of ZBR– T curves measured at different magnetic fields.…”

Квантовые поправки и магнитотранспорт в пленках 3D дираковского полуметалла Cd-=SUB=-3-x-=/SUB=-Mn-=SUB=-x-=/SUB=-As-=SUB=-2-=/SUB=-

“…Методом фотоэлектронной спектроскопии с угловым разрешением было показано, что Cd 3 As 2 обладает всеми перечисленными выше особенностями электронной структуры [7], что также подтверждается результатами зон-ных расчетов из первых принципов [8]. Кроме того, в Cd 3 As 2 наблюдался целый ряд необычных явлений, включая киральную аномалию, гигантское магнетосопротивление, а также недавно обнаруженную нетривиальную сверхпроводимость [9,10]. В отличие от Na 3 Bi, кристаллы Cd 3 As 2 стабильны на воздухе, что делает их более привлекательными для исследования.…”