VORTEX DYNAMICS IN A THIN MESOSCOPIC SUPERCONDUCTOR WITH HOLES UNDER AC MAGNETIC EXCITATION
Danielly Brito, Talles Benites, Rafael Zadorosny
São Paulo State University (UNESP), School of Engineering, Ilha Solteira Campus
Abstract
Along with the advances in nanofabrication, the superconductors became suitable for a wide range of applications, including superconducting rectifiers, single photon detectors, and quantum computing technologies. However, at the presence of time-varying signals, the vortex motion induces dissipative heating within the material, which can lead to significant energy loss, increasing the cooling demand, and generating noise interference within quantum devices. To control the vortex motion, studies emerged regarding pinning landscapes designed with various topological and geometrical properties [1, 2]. In this context, this work provides a theoretical approach to a superconducting system containing a square-shaped array of holes under the application of alternating magnetic fields superimposed on a static one.
The Time-Dependent Ginzburg-Landau (TDGL) equations were discretized using the link-variable method [3], and the solutions were obtained by implementing in FORTRAN 90. The system consisted of a 2D cell containing 36 square-shaped holes, subjected to a static perpendicular magnetic field - 0.10 of the upper critical field (Hc2) - , fixed with an oscillating field of amplitude ranging from 0.15 to 0.47 Hc2. For each amplitude, energy dissipation was calculated over the last period of oscillation, revealing its non-linear growth with the field’s intensity characterized by distinct regimes.
In the first regime, corresponding to the Meissner State, the curve showed a slight slope. Afterward, a more pronounced increase in the dissipation in the second regime was marked by the Mixed State transition and the filling of the defects, from outermost to innermost layers. The Lorentz force from the pinned flux led subsequent vortices to get trapped into interstitial regions. At the amplitude of 0.31 Hc2 the energy dissipation significantly increases due to depinning of vortices from the outermost layer of holes, which diminished the flux trapping potential presented in the previous regime. Therefore, in the fourth regime the flux motion overcomes the attraction potential from the pinning sites, rapidly driving the superconducting system toward the normal state.
In conclusion, the efficiency of the defects array is strongly dependent on the magnetic field amplitude. At this point, the defects are filled layer-by-layer as the field increases. Moreover, repulsive interactions from the trapped vortices drive vortex pinning into interstitial regions. Above the depinning amplitude, the expulsion of vortices from the outer defects triggers a flux motion, leading to a sharp increase in hysteretic losses.
ACKNOWLEDGMENTS:
CNPq. grant 310428/2021-1, and CAPES, financial code 001.
REFERENCE:
[1] J. I. Martin et al., Phys. Rev. Lett., vol. 79, p. 1929, 1997.
[2] R. C. dos Santos et al., Phys. Lett. A, vol. 458, p. 128595, 2023.
[3] H. G. Kaper and M. K. Kwong, J. Comput. Phys., vol. 119, p. 120, 1995.
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