Enhancement of the lower critical field in FeSe-coated Nb structures for superconducting radio-frequency applications

Abstract

Bulk Nb superconducting radio-frequency (SRF) cavities are widely used in accelerators, and their accelerating gradient and general performance are limited by the superheating field (B sh). To push the theoretical limit of the B sh, new multilayer structures are required. We fabricated FeSe-coated Nb films using pulsed laser deposition, performed structural characterizations, and measured the transport and magnetic properties for this superconductor-superconductor bilayer structure with smooth surface. Additionally, the measured B c1 of FeSe-coated Nb film is greatly enhanced, while the B sh of the FeSe layer is expected to be higher than that of bulk Nb, yet the superconducting transition temperature (T c) is less than 5 K. This work presents the first fabrication of a new coating layer: FeSe deposited on Nb, showing the possibility of using iron-based materials for multilayer structures in SRF cavities.

Pressure Evolution of Ultrafast Photocarrier Dynamics and Electron–Phonon Coupling in FeTe0.5Se0.5

“…The iron chalcogenides (FeTe Se ) have ignited the research field of unconventional superconductors because of many novel properties such as the high-temperature superconductivity [ 1 , 2 , 3 ], the high optical absorption coefficient for fabricating the photo-sensing device [ 4 , 5 , 6 ], and the high superheating field for realizing radio-frequency cavities [ 7 ]. Although constructed with the typical layered structure like other iron-based [ 8 , 9 ] and cuprate superconductors [ 10 , 11 ], iron chalcogenides possess the simplest crystal structure, making them much easier to produce [ 1 ].…”

“…Although constructed with the typical layered structure like other iron-based [ 8 , 9 ] and cuprate superconductors [ 10 , 11 ], iron chalcogenides possess the simplest crystal structure, making them much easier to produce [ 1 ]. The crystallized structure with a high superheating field allows iron chalcogenides to have much longer wavelengths, compared with the glassed chalcogenides [ 12 , 13 , 14 , 15 ], to be coated as a multilayer structure for realizing superconducting radio-frequency cavities [ 7 ]. Combining superconducting properties with acousto-optical properties in iron chalcogenides holds attractive application prospects.…”

“…This indicates a universal picture of the pairing mechanism of iron chalcogenides. The conspicuous rising of and the multilayer structure in nanoscale also imply broader prospects in the field of superconducting acousto-optic applications [ 7 ]. However, unlike FeSe, the role of EPC in FeTe Se has rarely been discussed.…”

Effects of nonmagnetic impurities and subgap states on the kinetic inductance, complex conductivity, quality factor and depairing current density

“…The depairing current density J d is related to the bias current of SSPD and is the maximum current that SRF cavities and superconducting cables can support. The screening current density on the inner surface of the cutting-edge Nb cavity reaches a current density close to J d , and SRF researchers study next-generation cavities using alternative materials with higher J d theoretically [64][65][66][67][68][69] and experimentally [70][71][72][73][74][75][76][77][78][79][80].…”

Determining the absolute value of magnetic penetration depth in small-sized superconducting films

“…Third, according to the London phenomenological model, λ 2 is proportional to the effective mass, m * , which could directly reflect the impact of a quantum critical point [10][11][12]. In addition, the performances of most applicable superconducting devices depend on λ, e.g., the surface resistance, R s , of microwave filters [13] and the superheating field, B sh , of radio-frequency cavities in accelerators [14,15]. That is, high-precision measurement of the absolute value of λ is crucial for elucidating the mechanism of superconductivity and exploring the applications of superconductors.…”