Lake, B.; Lefmann, K.; Christensen, N.B.; Aeppli, G.; McMorrow, D.F.; Ronnow, H.M.; Vorderwisch, P.; Smeibidl, P.; Mangkorntong, N.; Sasagawa, T.; Nohara, M.; Takagi, H.: Three-dimensionality of field-induced magnetism in a high-temperature superconductor. Nature Materials 4 (2005), p. 658-662
10.1038/nmat1452
Abstract:
Many physical properties of the high-temperature (high Tc) superconductors are two-dimensional phenomena derived from their square planar CuO2 building blocks. This is especially true of the magnetism from the copper ions electronically connected to each other via the p-orbitals of intervening oxygen atoms. As mobile charge carriers enter the CuO2-layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge carrier densities, the quantum fluctuations are sufficiently suppressed to yield static long-period order, and external fields also induce such order. Here we show that in contrast to the chemically-controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO2 planes. The results are important because they show that there are three-dimensional magnetic couplings which survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for the three-dimensional superconductivity. Both types of coupling will straighten the vortex lines, implying that we have finally established a direct link between technical superconductivity, which depends on the dynamics of the vortex lines, and the underlying antiferromagnetism of the cuprates.