First Observation of Nonreciprocal X-Ray Gyrotropy

We report the first observation of a nonreciprocal x-ray linear dichroism caused by the time-reversal odd, real part $\zeta$ of the complex gyrotropy tensor ${\zeta }^{*}$ which is dominated by electric dipole-electric quadrupole $E1E2\mathrm{}$ interference terms. A nonreciprocal transverse anisotropy was observed in the low temperature insulating phase of a Cr doped ${\mathrm{V}}_2{\mathrm{O}}_3$ Mott crystal when a single antiferromagnetic domain was grown by magnetoelectric annealing along the hexagonal c axis. This new element (edge) specific spectroscopy could nicely complement x-ray magnetic circular dichroism which is silent for antiferromagnetic materials.