Members of the SPIN team can now deposit single crystal thin film superconductors with thickness down to few nanometers by using the TUBE DAUM. The magnetic properties of these thin films were found to be quite different from the ones in thicker film and in bulk superconductors. 

Isothermal diamagnetic response to an external magnetic field, due to Meissner currents, is a macroscopic signature of superconductivity. Below their critical temperature (T_c) and above their first critical field (H_c1), type II superconductors host vortices which reduces the Meissner diamagnetic signal until full cancellation at the second critical field (H_c2), where the superconductor turns to normal state. Therefore, the macroscopic magnetic moment (M) of a superconductor is a good probe of the mixed-state of type-II superconductor and vortex lattice phases. In the present contribution, we report on the study of magnetic moment of thin films of various conventional type-II superconductors (MgB₂, NbN, Nb and V) with thicknesses ranging from 100 nm down to 5 nm, as a function of applied magnetic field (H) and temperature (T). When H is applied perpendicular to the film plane, SQUID measurements enlighten an inverted M vs H loop as compared to typical curves for films thicker than 100 nm or bulk samples. We systematically analyzed the influence of film thickness (t) and T on the stability of the observed field-induced “paramagnetic-like” state and argue that these dependences pinpoint the role of low pinning, geometry-enhanced London penetration length and thin film edge demagnetization fields.

To know more about these results: 10.1103/PhysRevB.110.094502 or hal-04716602

Beyond the study of the thin film superconductors intrinsic features, the control of the growth of superconducting films opens the way to deposit more complex stacks, especially using ferromagnetic materials, to develop superconducting spintronic. Another article was recently published about the spin-injection in superconductive single crystal MgB₂ thin films studied by FMR ( 10.1063/5.0220815 ).

These works were supported by the « SONOMA» project co-funded by FEDER-FSE Lorraine et Massif des Vosges 2014-2020, a European Union Program, and by the French National Research Agency through the France 2030 government grants PEPR SPIN ANR-22-EXSP 0008.