Superconducting Vortex with Antiferromagnetic Core

We show that a superconducting vortex in underdoped high T{sub c} superconductors could have an antiferromagnetic core. This type of vortex configuration arises as a topological solution in the recently constructed SO(5) nonlinear {sigma} model and in Landau-Ginzburg theory with competing antiferromagnetic and superconducting order parameters. Experimental detection of this type of vortex by muon spin resonance and neutron scattering is proposed. {copyright} {ital 1997} {ital The American Physical Society}