Preparation and characterization of high-entropy alloy (TaNb)1−x(ZrHfTi)x superconducting films

Abstract

We report on the preparation and the physical properties of superconducting (TaNb) 1− (ZrHfTi) high-entropy alloy films. The films were prepared by means of magnetron sputtering at room temperature, with ranging from 0 to 1 with an average thickness of 600 -950 nm. All films crystallize in a pseudo body-centered cubic (BCC) structure. For samples with < 0.65, the normal-state properties are metallic, while for ≥ 0.65 the films are weakly insulating. The transition from metallic to weakly insulating occurs right at the near-equimolar stoichiometry. We find all films, except for = 0 or 1, to become superconducting at low temperatures, and we interpret their superconducting properties within the Bardeen-Cooper-Schrieffer (BCS) framework. The highest transition temperature Tc = 6.9 K of the solid solution is observed for ~0.43. The highest upper-critical field Bc2(0) = 11.05 T is found for the near-equimolar ratio ~0.65, where the mixing entropy is the largest. The superconducting parameters derived for all the films from transport measurements are found to be close to those that are reported for amorphous superconductors. Our results indicate that these films of high-entropy alloys are promising candidates for superconducting device fabrication.

Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research

“…One presented the successful preparation of thin film HEA superconductors (TaNb) 1−x (HfZrTi) x using a magnetron sputtering method (No. 21 in Table 1) [23]. The films with x < 0.65 showed normal metallic properties; on the other hand, those with x > 0.65 exhibited weakly insulating behaviors.…”

“…The pioneering review [16] of HEA superconductors proposed a thin film HEA and the need for the evaluation of J c , which have both recently been realized [18,23]. These kinds of research will be constantly carried out.…”

Materials Research on High-Entropy Alloy Superconductors

“…On the other hand, transition metal amorphous superconductors do not follow this rule and frequently show relatively high T c values in the valley of the curve of the Matthias rule [16]. HEA superconductors with simple crystal structures have been found in bcc [17][18][19][20][21][22] and hcp [23][24][25][26]. The T c vs. VEC plots of these HEAs seem to fall between a crystalline curve and an amorphous one [27,28].…”

High critical current density and high-tolerance superconductivity in high-entropy alloy thin films

“…1b shows a cross-sectional scanning electron microscopy (SEM) image of the lm fabricated at T s = 520 °C with a thickness of approximately 700 nm. The slight peak shift and low intensity for the thin lms fabricated at T s values other than 520 °C are more closely related to the substrate temperature than the compositional ratio of the lms 12,13 (see Table S1 and Figs. S1 and S2 in SI).…”

“…However, the μ 0 H c2 (0) of the thin lms fabricated at temperatures above the optimal T s = 520 °C showed a more rapid reduction compared to the decrease in T c . Despite the high T c , small slope values of (dH c2 /dT) T=Tc have also been reported in (TaNb) 1-x (HfZrTi) x HEA superconductors by controlling the mixing entropy or application of pressure 5,12,13 . Typically, because the SC coherence length (x) in dirty type-II superconductors is proportional to the mean free path (l) of the charge carriers, H c2 (0) can be improved by adjusting the disorder level 19,20 .…”