Abstract
Muon spin relaxation/rotation (muSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unconventional superconductivity of cuprates and Fe-based high-temperature superconductors, which remain a puzzle. Very recently double layered Fe-based super-conductors having quasi-2D crystal structures and Cr-based superconductors with a quasi-1D structure have drawn considerable attention. Here we present a brief review of the characteristics of a few selected Fe- and Cr-based superconducting materials and highlight some of the major outstanding problems, with an emphasis on the superconducting pairing symmetries of these materials. We focus on muSR studies of the newly discovered superconductors ACa2Fe4As4F2(A = K, Rb, and Cs), ThFeAsN, and A2Cr3As3(A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states. We also briefly discuss the results of muSR investigations of the superconductivity in hole and electron doped BaFe2As2.
Highlights
In 1911, Kamerlingh Onnes measured the electrical conductivity of numerous metals and discovered the abrupt disappearance of the resistance of a solid mercury wire in liquid helium[1]
We focus on μSR studies of the newly discovered superconductors ACa2Fe4As4F2 (A = K, Rb, and Cs), ThFeAsN, and A2Cr3As3 (A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states
A wide range of superconductors have been found with increasing high transition temperatures (Tc), and it is hoped that a roomtemperature superconductor can be realized
Summary
Muon spin rotation and relaxation are very sensitive local probes which can be used to investigate magnetic and superconducting materials The breaking of TRS in the superconducting state can be inferred from either an increase of λ66,73, or σKT 74 below Tc. The application of a longitudinal field (LF) parallel to the initial muon-spin serves to decouple the muon from the local magnetic fields in the sample. The application of a longitudinal field (LF) parallel to the initial muon-spin serves to decouple the muon from the local magnetic fields in the sample This decoupling occurs more rapidly for static fields than for dynamic fields, and LF-μSR reveals information about both the magnitude and dynamics of the internal fields[104]. ΜSR measurements in applied transverse magnetics field (TF), perpendicular to the initial muon spin direction, are important for probing the flux line lattice[106]. By analyzing σsc with various gap models, the magnitude and structure of the superconducting gap can be probed, which in turn allows for the identification of the superconducting pairing symmetry
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