Controlling superconductivity of CeIrIn$_5$ microstructures by substrate selection

Abstract

Superconductor/metal interfaces are usually fabricated in heterostructures that join these dissimilar materials. A conceptually different approach has recently exploited the strain sensitivity of heavy-fermion superconductors, selectively transforming regions of the crystal into the metallic state by strain gradients. The strain is generated by differential thermal contraction between the sample and the substrate. Here, we present an improved finite-element model that reliably predicts the superconducting transition temperature in CeIrIn 5 even in complex structures. Different substrates are employed to tailor the strain field into the desired shapes. Using this approach, both highly complex and strained as well as strain-free microstructures are fabricated to validate the model. This enables full control over the microscopic strain fields, and forms the basis for more advanced structuring of superconductors as in Josephson junctions. Main textThe local and selective transformation of materials properties forms the basis of electronics. In the transistor, for example, electric fields drive the transition between an insulator and a metallic conductor. In correlated electron systems, phase transformations can be driven via relevant tuning parameters, such as strain. In thin film materials, strains caused by mismatch between substrate and film have been investigated for a long time 1 . Such mismatch strains can either be a nuisance, as a source of dislocations and materials incompatibility, or a blessing, leading to desirable band structure modifications. Each film thus presents a new challenge in finding the right substrate to achieve the desired level of strain 2-4 . In bulk crystals, however, strain and strain gradients are usually weak. When it is desirable to purposely induce strain, often an elaborate straining apparatus is required 5,6 .