Transition of a small-bipolaron gas to a Frohlich polaron in a deformable lattice

• Main Authors: Hettiarachchi, Gayan Prasad, Mohd. Muhid, Mohd. Nazlan, Hamdan, Halimaton
• Format: Article
• Published: American Physical Society 2018
• Subjects: QD Chemistry
• Online Access: http://eprints.utm.my/id/eprint/85472/; http://dx.doi.org/10.1103/PhysRevB.97.155142

The electronic properties of guest Cs atoms in a deformable lattice are investigated at various densities n. Low values of n show optical absorptions of small bipolarons. At intermediate n values, new bands appear in the midinfrared (MIR) and high-frequency regions, which coexist with the small bipolaron bands. With a further increase in n, the small bipolaron bands become less discernible and subsequently disappear, resulting in the appearance of a Drude component superimposed on a MIR sideband suggesting a phase transition to a polaronic metal. In this itinerant phase, an approximately twofold mass enhancement is observed. This continuous transition of a gas of small bipolarons to a polaronic metal characterized by a Fröhlich polaron reveals an important part of the complex phase diagram of the metal-insulator transition in a deformable lattice.