Superconductors with enhanced superconducting critical temperatures (T_c) above the boiling point of liquid helium (4.2 K) are of interest for interconnections in superconducting quantum computing systems to avoid ohmic heating[1]. Crystalline Re in bulk is a type-I superconductor with a Tc of about 1.7K[2]. An elevated T_c up to about 6K in electrodeposited amorphous Re has been reported[3]. In addition, various elevation in Tc has also been reported for Re film under shear strain[4] or doped with foreign elements such as Tungsten (W), Osmium (Os), and Carbon (C)[5, 6].

This work aims to test a hypothesis that the T_c of electrodeposited Re films can be tuned using compressive and tensile strains on the Re films generated with thermal expansions difference. Figure 1 shows a diagram of the strains on Re film sandwiched between metals with different coefficients of thermal expansions (CTEs) when the temperature is lowered. For example, Cu has a higher CTE than Re and Cr has a slightly lower CTE than Re. Such sandwich structures are prepared at room temperature using electrochemical deposition. The DC resistance measurements at cryogenic temperatures confirmed that the superconducting transition for the Re films sandwiched between Cu occurs at a lower temperature than the Re film alone. On the other hand, when Cr is used, the sandwiched Re structure shows a slightly enhanced superconducting critical temperature. The effect of thermal annealing i.e., the recrystallization of electrodeposited Re films at an elevated temperature, and electrochemical behavior of Re, Cr, and Cu electrodeposition will be discussed in the talk.

References

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4. Mito, M., et al., Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain. Scientific Reports, 2016. 6(1): p. 36337.
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