  The Sakai-Sugimoto model provides a holographic description for chiral
symmetry breaking. We use this model to investigate chirally broken phases in
an external magnetic field at finite isospin and baryon chemical potentials.
The equations of motion for the bulk gauge fields are solved analytically and
the free energy is computed from the Yang-Mills and Chern-Simons contributions
to the D8 brane action. In the case of a neutral pion condensate, a magnetic
field is found to induce nonzero gradients of the Goldstone boson fields
corresponding to meson supercurrents. A charged pion condensate, on the other
hand, expels the magnetic field due to the Meissner effect. Upon comparing the
Gibbs free energies of these two phases we find that the rotation of the chiral
condensate into a charged pion condensate for finite isospin chemical
potentials is partially undone by switching on a magnetic field, and we
determine the critical magnetic field which removes the charged pion condensate
in a first-order phase transition.
