Fig. 2: Geometric string theory of the two-channel model.
From: Feshbach hypothesis of high-Tc superconductivity in cuprates
a Magnetic polarons, i.e., (sc) mesons, are fermionic quasiparticles of single holes doped into an AFM Mott insulator. In contrast, tightly bound (cc) mesons exist as long-lived s- and d-wave resonances in the spectrum. The two types of mesons constitute open and closed scattering channels, and can be described in a truncated string basis defined in a classical Néel background (see insets); they are composed of chargons (white circles) connected to a spinon (bottom) or another chargon (top) at the opposite end of the string. The potential curves of the open and closed scattering channels are sketches to illustrate the analogy to the Feshbach mechanism familiar from atomic physics. We plot the (cc) excitation spectrum at Q = 0 obtained from the string model88 (left) and from DMRG studies in the t-J model48 (right), which shows the large energy separation between the s-wave and d-wave (cc) resonances. b Two spinons, each bound to a single chargon, can recombine into a longer string connecting the two chargons. Thereby spin exchange J⊥ and NNN tunneling \({t}^{{\prime} }\) processes couple the open and closed channel states and mediate an effective scattering interaction between the former.
