Modeling Field-Induced Superconductivity in Magnetic Impurity Materials

Magnetic fields and magnetic impurities each lower the transition temperature T_c in spin-singlet superconductors by breaking time-reversal symmetry. When they interact, however, the field can polarize these impurities, suppressing the spin-flip scattering rate and lowering the impurities’ pair-breaking effect as H increases. In some thin-film systems this effect is large enough such that T_c no longer decreases monotonically with H, resulting in field-enhanced and even field-induced superconductivity. We observe field-enhanced and field-induced effects in thin-film Ce-doped LaSb₂. Using the Kharitonov-Feigelman model [1], we explain these results and develop methods to analyze the contributions of competing pair-breaking effects. We model the superconducting dome over the parameter space of possible samples, opening the door to theory-driven sample design. These insights enable experimentalists to better understand observations of reentrant, field-enhanced and field-induced superconductivity, and to tune between depairing regimes.

[1] Kharitonov, M. Yu. & Feigelman, M. V. Enhancement of Superconductivity in Disordered Films by Parallel Field. JETP Letters 82, 421–425 (2005).