Study of superconductivity in quantum materials using controlled disorder

Abstract

Understanding superconductivity in quantum materials requires tuning the system with several tuning parameters like pressure, magnetic field, chemical doping, and innovative probing techniques, among which controlled disorder, such as electron and proton irradiation, stands out. In particular, for unconventional superconductors whose superconductivity appears near the different types of long-range order like magnetism and charge order, the two phases can be tuned using controlled disorder, allowing for a better understanding of these existing phases. Moreover, controlled disorder can be used to study the vortex properties of type-II superconductors by tuning the defect concentration inside the sample.

In this work, we utilized London penetration depth measurement to study the bulk superconductivity of topological superconductor candidates: 2M-WS2 and LaNiGa2. In addition, we studied their response to non-magnetic disorder to understand superconducting order parameter and pairing states. Similarly, we studied the superconducting properties of ferromagnetic superconductor, EuFe2(As1−xPx)2. By doing electron irradiation, we studied the superconducting state in both ferromagnetic and paramagnetic backgrounds. Then, we applied the electron irradiation to intentionally induce point defects in Ca3Rh4Sn13 and measured the Campbell length at high frequencies. We observed the disorder-induced peak effect, which is static, by frequency-dependent measurements. Finally, we experimentally verified the theoretically predicted non-monotonic relaxation of Campbell length due to creep-enhanced vortex creeping by measuring the Campbell relaxation, which is not detected in conventional magnetic measurement.