No mixing of superconductivity and antiferromagnetism in a high-temperature superconductor

Abstract

There is still no universally accepted theory of high-temperature superconductivity. Most models assume that doping creates 'holes' in the valence band of an insulating, antiferromagnetic 'parent' compound, and that antiferromagnetism and high-temperature superconductivity are intimately related. If their respective energies are nearly equal, strong antiferromagnetic fluctuations (temporally and spatially restricted antiferromagnetic domains) would be expected in the superconductive phase, and superconducting fluctuations would be expected in the antiferromagnetic phase; the two states should 'mix' over an extended length scale. Here we report that one-unit-cell-thick antiferromagnetic La2CuO4 barrier layers remain highly insulating and completely block a supercurrent; the characteristic decay length is 1 A, indicating that the two phases do not mix. We likewise found that isolated one-unit-cell-thick layers of La1.85Sr0.15CuO4 remain superconducting. The latter further implies that, on doping, new electronic states are created near the middle of the bandgap. These two findings are in conflict with most proposed models, with a few notable exceptions that include postulated spin-charge separation.

Bose–Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

“…As mentioned in section 1, the chemical potential µ remains in the charge-transfer gap of doped cuprates like La 2−x Sr x CuO 4 [7] because of bipolaron formation. The condensate wave function, ψ(Z), is described by the Gross-Pitaevskii (GP) equation.…”

Nonequilibrium transport and optical properties of model metal–Mott-insulator–metal heterostructures

“…Detailed analysis of the transport properties of correlated heterostructures including current-voltage characteristics is directly relevant to device applications. 10,11,12,13 However, this area remains largely unexplored.…”

Insights from the study of high-temperature interface superconductivity

“…As is well known, if the chemical potential of the constituent materials is different when they are separated, once they are brought in contact, the carriers redistribute across the interface in such a way that the chemical potential equalizes. In 2003, it was shown by Bozovic et al [4] that no charge redistribution occurs between La 1.85 Sr 0.15 CuO 4 and La 2 CuO 4 . The measurement in M-I bilayers was performed by Smadici et al [5] using a novel synchrotron-based technique, resonant soft X-ray scattering.…”