Stripe as an effective one-dimensional band of composite excitations

The microscopic structure of a charge stripe in an antiferromagnetic insulator is studied within the ${t-J}_z$ model using analytical and numerical approaches. We demonstrate that a stripe in an antiferromagnet should be viewed as a system of composite holon-spin-polaron excitations condensed at the self-induced antiphase domain wall (ADW) of the antiferromagnetic spins. The properties of such excitations are studied in detail with numerical and analytical results for various quantities being in very close agreement. A picture of the stripe as an effective one-dimensional (1D) band of such excitations is also in very good agreement with numerical data. These results emphasize the primary role of kinetic energy in favoring the stripe as a ground state. A comparative analysis suggests the effect of pairing and collective meandering on the energetics of the stripe formation to be secondary. The implications of this microscopic picture of fermions bound to the 1D antiferromagnetic ADW for the effective theories of the stripe phase in the cuprates are discussed.