Vortex penetration field measurement system based on third-harmonic method for superconducting RF materials

Abstract

We develop a lower critical field (H c1 ) measurement system using the third-harmonic response of an applied AC magnetic field from a solenoid coil positioned above a superconducting sample. Parameter H c1 is measured via detection of the third-harmonic component, which drastically changes when a vortex begins to penetrate the superconductor with temperature increase. The magnetic field locally applied to one side of the sample mimics the magnetic field within superconducting radio-frequency (SRF) cavities and prevents edge effects of the superconducting sample. With this approach, our measurement system can potentially characterize surface-engineered SRF materials such as Superconductor-Insulator-Superconductor multilayer structure (S-I-S structure). As a validation test, we measure the temperature dependence of H c1 of two high-RRR bulk Nb samples and obtain results consistent with the literature. We also confirm that our system can apply magnetic fields of at least 120 mT at 4-5 K without any problem of heat generation of the coil. This field value is higher than those reported in previous works and makes it possible to more accurately estimate H c1 at lower temperatures.

Superfluid flow in disordered superconductors with Dynes pair-breaking scattering: depairing current, kinetic inductance, and superheating field

“…( 63) is not applicable to these structure because j s (x) takes the maximum at the inside (x 0 > 0). Study on effects of Γ on H sh in these structures would be useful for comparison of the theory and experiments [87][88][89][90][91][92][93][94][95][96][97][98][99][100].…”

Superheating fields of semi-infinite superconductors and layered superconductors in the diffusive limit: structural optimization based on the microscopic theory

“…Progress in experiments is summarized in [22] (see also progress in the last several years, e.g. [23][24][25][26][27][28][29][30][31][32][33][34]).…”

Complex AC Magnetic Susceptibility as a Tool for Exploring Nonlinear Magnetic Phenomena and Pinning Properties in Superconductors

“…This allows high measurement precision (accuracy and resolution) close to the performance of AC/DC SQUID magnetometers. Another advantage is the high sensitivity of the ACMS harmonic components to the broad set of experimental degrees of freedom such as the temperature (T), the amplitude (H ac ) and frequency ( f ) of the AC magnetic field, the bias DC field (µ 0 H dc ) and the sample geometry [7][8][9][10][11].…”