Optical properties of small polarons from dynamical mean-field theory
S. Fratini
Laboratoire d'Etudes des Proprietes Electroniques des Solides - CNRS
BP 166, F-38042 Grenoble Cedex 9, France
S. Ciuchi
Istituto Nazionale di Fisica della Materia and
Dipartimento di Fisica, Universita dell'Aquila,
via Vetoio, I-67010 Coppito-L'Aquila, Italy
In many classes of compounds, including the crystalline organic semiconductors, the
carriers can be strongly coupled to the lattice degrees of freedom, leading to the
formation of polarons. Here we study the optical properties of small polarons in the
framework of the Holstein model, by applying the dynamical mean-field theory. This
approach allows to enlighten important quantitative and qualitative deviations from the
standard treatments of small polaron theory, that should be taken into account when
interpreting experimental data. In particular, characteristic features emerge in the
adiabatic regime (i.e. when the lattice dynamics are slow compared with the electron
motion) at intermediate values of the electron-lattice interaction strength, which are
distinctive of the polaron crossover, and for which analytical expressions are provided.