Effect of antiferromagnetic planes on the superconducting properties of multilayered high-Tc cuprates

Insights from angle-resolved photoemission spectroscopy of an undoped four-layered two-gap high-T(c) superconductor

An undoped cuprate with apical fluorine and inner (i) and outer (o) CuO(2) layers is a 60 K superconductor whose Fermi surface has large n- and p-doped sheets with the superconducting gap on the n sheet twice that on the p sheet. The Fermi surface is not reproduced by the local density approximation, but the screening must be substantially reduced due to electronic correlations, and oxygen in the o layers must be allowed to dimple outwards. This charges the i layers by 0.01|e|, causes a 0.4 eV Madelung-potential difference between the i and o layers, quenches the i-o hopping, and localizes the n sheets onto the i layers, thus protecting their d-wave pairs from being broken by scattering on impurities in the BaF layers. The correlation-reduced screening strengthens the coupling to z-axis phonons.

0-pi transitions in Josephson junctions with antiferromagnetic interlayers

We show that the dc Josephson current through superconductor-antiferromagnet-superconductor (S-AF-S) junctions manifests a remarkable atomic-scale dependence on the interlayer thickness. At low temperatures the junction is either a 0 or pi junction depending on whether the AF interlayer consists of an even or odd number of atomic layers. This is associated with different symmetries of the AF interlayers in the two cases. In the junction with odd AF interlayers an additional pi- 0 transition can take place as a function of temperature. This originates from the interplay of spin-split Andreev bound states. Experimental implications of these theoretical findings are discussed.

Uniform mixing of high-Tc superconductivity and antiferromagnetism on a single CuO2 plane of a Hg-based five-layered cuprate

We report a site selective Cu-NMR study on underdoped Hg-based five-layered high-Tc cuprate HgBa2Ca4CU5O(12+delta) with a Tc = 72 K. Antiferromagnetism (AFM) has been found to take place at T(N) = 290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69 microB at three inner planes (IP). This value is comparable to the values reported for nondoped cuprates, suggesting that the IP may be in a nearly nondoped regime. Most surprisingly, the AFM order is also detected with M(AFM)(OP) = 0.1 microB even at two outer planes (OP) that are responsible for the onset of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AFM at OP's. This is the first microscopic evidence for the uniform mixed phase of AFM and SC on a single CuO2 plane in a simple environment without any vortex lattice and/or stripe order.