Microwave Superconductivity

  • Resonant microwave techniques are powerful tools to investigate the properties of superconductors (SC), in particular to determine the penetration depth, superfluid density, quasiparticle conductivity, and in general the complex impedance. Our approach to the issue is the use of coplanar waveguide resonators (CPWR), in two different configurations (all details here).
  • Briefly: in one case we fabricate a CPWR from a thin film of the SC under study, and by analyzing the resonance curves as a function of temperature with a proper parametric model we extract the physical parameters. We used this technique to characterize the microwave linear and nonlinear response of YBa2Cu3O7-x and MgB2 thin films.
  • On the other hand, the microwave properties of small single crystals can be deduced by coupling them to an already characterized CPWR and by analyzing the changes they cause to the CPWR resonance frequency and quality factor, in a resonator-perturbation approach. From these changes, the complex permittivity and complex permeability of the sample (and in turn its complex ac susceptibility) can be determined. We used this technique to extensively study several families of the iron-based superconductors (IBS), mainly the Ba-122 family (BaFe2As2-based, with different kinds of chemical doping to induce superconductivity), but also 11 (FeSe1-xTex), 1144 (CaKFe4As4), 12442 (RbCa2Fe4As4F2), and the Eu-122 ferromagnetic superconductor.
  • This contactless technique is also reliable to study the effects of introducing artificial defects into the system - e.g. through ion irradiation - by measuring the same crystal before and after treatment, to avoid sample to sample variability. This allowed us to investigate the fundamental properties of IBSs by studying their dependence on structural disorder, e.g. in the case of their multigap structure, the symmetry of the order parameter, and the anisotropy of the penetration depth.
  • Illustrative publications on the topic

  • G. Ghigo and D. Torsello - Microwave Analysis of Unconventional Superconductors with Coplanar-Resonator Techniques - Springer: Berlin/Heidelberg, Germany, (2022)
  • G. Ghigo, M. Fracasso, R. Gerbaldo, L. Gozzelino, F. Laviano, A. Napolitano, G.-H. Cao, M. Graf, R. Prozorov, T. Tamegai, Z. Shi, X. Xing and D. Torsello - High-Frequency ac Susceptibility of Iron-Based Superconductors - Materials 15, 1079 (2022)
  • D. Torsello, E. Piatti, G. Ummarino, X. Yi, X. Xing, Z. Shi, G. Ghigo, and D. Daghero - Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2 - npj Quantum Mater. 7, 10 (2022)
  • D. Torsello, L. Gozzelino, R. Gerbaldo, T. Tamegai and G. Ghigo - Scaling laws for ion irradiation effects in iron-based superconductors - Sci. Rep. 11, 5818 (2021)
  • A. R. Medema, G. Ghigo, and S. K. Remillard - Influence of columnar defects on magnetic relaxation of microwave nonlinearity in superconducting YBCO resonator devices - Physica C 583, 1353849 (2021)
  • D. Torsello, and G. Ghigo - A Coplanar Waveguide Resonator Technique for the Characterization of Iron-Based Superconductors - Proceeding of the 2020 IEEE Ukrainian Microwave Week (UkrMW), 726 (2020)
  • D. Torsello, G.A. Ummarino, J. Bekaert, L. Gozzelino, R. Gerbaldo, M.A. Tanatar, P.C. Canfield, R. Prozorov, and G. Ghigo - Tuning the Intrinsic Anisotropy with Disorder in the CaKFe4As4 Superconductor - Phys. Rev. Appl. 13, 064046 (2020)
  • G. Ghigo, D. Torsello, L. Gozzelino, T. Tamegai, I. Veshchunov, S. Pyon, W. Jiao, G. Cao, S. Grebenchuk, I. Golovchanskiy, V. Stolyarov and D. Roditchev - Microwave analysis of the interplay between magnetism and superconductivity in EuFe2(As1−xPx)2 single crystals - Phys. Rev. Research 1, 033110 (2019)
  • D. Torsello, K. Cho, K. R. Joshi, S. Ghimire, G. A. Ummarino, N. M. Nusran, M. A. Tanatar, W. R. Meier, M. Xu, S. L. Bud’ko, P. C. Canfield, G. Ghigo, and R. Prozorov - Analysis of the London penetration depth in Ni-doped CaKFe4As4 - Phys. Rev. B 100, 094513 (2019)
  • D. Torsello, G. A. Ummarino, L. Gozzelino, T. Tamegai, G. Ghigo - Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2 - Phys. Rev. B 99, 134518 (2019)
  • G. Ghigo, D. Torsello, G. A. Ummarino, L. Gozzelino, M. A. Tanatar, R. Prozorov, and P. C. Canfield - Disorder-Driven Transition from s± to s++ Superconducting Order Parameter in Proton Irradiated Ba(Fe1−xRhx)2As2 Single Crystals - Phys. Rev. Lett. 121, 107001 (2018)
  • G. Ghigo, D. Torsello, R. Gerbaldo, L. Gozzelino, F. Laviano, T. Tamegai - Effects of heavy-ion irradiation on the microwave surface impedance of (Ba1−xKx)Fe2As2 single crystals - Supercond. Sci. Technol. 31, 034006 (2018)
  • Contacts

  • img Gianluca GHIGO
    Associate Profesor
    +39 0110907362
  • imgimgimg

  • img Daniele TORSELLO
    +39 0110904329
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    For collaborations, proposals, thesis requests, lab visits, please contact us:

    Phone: +39 0110907362
    Address: Corso Duca degli Abruzzi, 24 10129 Torino, ITALY
    E-mail: gianluca.ghigo@polito.it