Intrinsic EPR in La2-xSrxCuO4: Manifestation of Three-Spin Polarons

Electron-paramagnetic resonance (EPR) measurements on ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ provide experimental evidence of a three-spin polaron, consisting of two ${\mathrm{Cu}}^{2+}$ ions and one $p$ hole. The symmetry properties and the peculiar temperature dependence of the $g$ values of the EPR line indicate the presence of dynamical Jahn-Teller distortions and formation of a collective mode of polarons and surrounding strongly correlated Cu ions (bottlenecked regime).