Observable NMR signal from circulating current order in YBCO

Assuming, as suggested by recent neutron-scattering experiments, that a broken symmetry state with orbital current order occurs in the pseudogap phase of the cuprate superconductors, we show that there must be associated equilibrium magnetic fields at various atomic sites in the unit cell, which should be detectable by NMR experiments.

Figure 1

Top view of circulating currents in the Varma loop ordered state. Cu sites are black rectangles, O sites are white circles.

Figure 2

Microscopic model for YBCO. O sites are spheres, Cu sites are cubes.

Figure 3

Microscopic model for Hg1201. O sites are spheres, Cu sites are cubes.