  Spin-charge separation is known to be broken in many physically interesting
one-dimensional (1D) and quasi-1D systems with spin-orbit interaction because
of which spin and charge degrees of freedom are mixed in collective
excitations. Mixed spin-charge modes carry an electric charge and therefore can
be investigated by electrical means. We explore this possibility by studying
the dynamic conductance of a 1D electron system with image-potential-induced
spin-orbit interaction. The real part of the admittance reveals an oscillatory
behavior versus frequency that reflects the collective excitation resonances
for both modes at their respective transit frequencies. By analyzing the
frequency dependence of the conductance the mode velocities can be found and
their spin-charge structure can be determined quantitatively.
