Magnon-induced superconductivity in field-cooled spin-1/2 antiferromagnets

Abstract

If, during the preparation, an external magnetic field is applied upon cooling we say it has been field cooled. A novel mechanism for insulator-metal transition and superconductivity in field-cooled spin-1/2 antiferromagnets on bcc lattice is discussed. Applying a magnetic field along the sublattice B magnetization, we change the magnetic and transport properties of the material. There is a critical value Hcr1. When the magnetic field is below the critical one H < Hcr1 the prepared material is a spin−1/2 antiferromagnetic insulator. When H > Hcr1 the sublattice A electrons are delocalized and the material is metal. There is a second critical value Hcr2 > Hcr1. When H = Hcr2, it is shown that the Zeeman splitting of the sublattice A electrons is zero and they do not contribute to the magnetization of the system. At this quantum partial order point (QPOP) the sublattice B transversal spin fluctuations (magnons) interact with sublattice A electrons inducing spin anti-parallel p-wave superconductivity which coexists with magnetism. At zero temperature the magnetic moment of sublattice B electrons is maximal. Below the Néel temperature (TN ) the gap is approximately constant with a small increase when the system approaches TN . It abruptly falls down to zero at temperatures above TN .

Model for the field cooled and zero field cooled ferrimagnetic spinel

“…The potential V k depends on temperature since the Hartree-Fock parameter u does. Near the Néel temperature the parameter u decreases 55 and potential V k increases. Above Néel temperature the magnon opens a gap which rapidly increases when the temperature increases.…”

Superconductivity at metal-antiferromagnetic insulator interfaces

“…Theory predicts that magnons can mediate superconductivity in bulk antiferromagnets, with either p-wave or * Currently at the Norwegian Defence Research Establishment (FFI), NO-2027 Kjeller, Norway; eirik-lohaugen.fjarbu@ffi.no d-wave pairing symmetry [17,18]. There are also suggestions that magnons mediate superconductive pairing in iron pnictides [19,20].…”

“…Theory predicts that magnons can mediate superconductivity in bulk antiferromagnets, with either p-wave or d-wave pairing symmetry [17,18]. There are also suggestions that magnons mediate superconductive pairing in iron pnictides [19,20].…”