Events in Physics

Pulsed-Magnetic-Field Studies of the Cuprate and FeAs-based 'High-Tc' Superconductors

Pulsed magnetic fields of up to 85 T at Los Alamos have been employed in the study of cuprate and FeAs-based “high-temperature” superconductors. The large magnetic fields are necessary to overcome the robust superconducting states to reveal the normal-state properties. 

 

In single crystals of the underdoped cuprates, Shubnikov-de Haas and de Haas-van Alphen oscillations reveal between one and three small Fermi-surface pockets, comprising a few percent of the Brillouin-zone area. I will describe how these pockets, representing a reconstruction of the original large hole Fermi surface, can be reconciled with neutron-scattering and ARPES data. In addition, I suggest a connection between the Fermi-surface instability that leads to nesting and the mechanism for cuprate superconductivity.

 

Single crystals of the recently-discovered (A,K)Fe₂As₂ (A=Ba, Sr) family of superconductors have also been studied using high fields, revealing rather isotropic upper critical fields; no other layered superconductor that we know exhibits upper critical fields that behave in this way. The difference is associated with the compounds’ distinctive Fermi-surface topology, the strong corrugations of which – a manifestation of essentially three-dimensional bandstructure - permit orbital limiting of the upper critical field at all field orientations. Therefore the 112-type ternary iron arsenides are unique in possessing both a rather high critical temperature and essentially three-dimensional electronic properties. In contrast to common assumptions based on the properties of the cuprates, it seems that reduced dimensionality is not necessarily a prerequisite for “high-temperature” superconductivity.