Large (bi)Polarons for Novel Energy Conversion and Superconductivity

Abstract

The last fifty years produced fundamental advances in understanding the formation, motion and interactions among (bi)polarons. Interference between the atomic displacement patterns of oppositely charged (bi)polarons generates a short-range repulsion which impedes their reconalmbination, significantly enhancing efficiencies of energy-conversion devices, e.g. perovskite solar cells. A large-(bi)polaron's atomic vibrations are softened by the relaxation of its self-trapped electronic carriers. Scattering of impinging ambient phonons by large-bipolarons' softened vibrations generates distinctive transport. Coherence between the softened atomic vibrations of large-bipolarons generates a phonon-assisted mutual attraction which facilitates their condensation into a liquid. A large-bipolaron liquid's superconducting Bose condensate is characterized by coherent zero-point atomic vibrations which decrease positron annihilation and increase ion channeling. Disorder can trigger electronic charge carriers' collapse into small polarons. The back-and-forth Arrhenius hopping of a small-polaron softens the associated atoms' vibrations thereby increasing their entropy. This effect explains the empirically observed Meyer-Neldel compensation effect. In particular, the temperature-independent factor of the jump-rate increases exponentially in proportion to its activation energy.

Observation of Negative Terahertz Photoconductivity in Large Area Type-II Dirac Semimetal PtTe2

“…It is noted that numerous publications have reported the polaron formation in perovskites and other polar solids due to the Fröhlich interaction, or strong electron-optical phonon coupling, and it has been proposed that the polaron formation allows to reduce the carrier mobility due to phonon ""dressing"" of carriers. [44][45][46][47] In some solids, the excess carriers interaction with surrounding atoms forms a distortion in the local bonding environment, resulting in its spatial localization. 48,49 The composite of electronic carrier and concomitant distorted local lattice is named polaron, a kind of quasiparticle that is self-trapped in a potential well that it creates.…”

Giant acceleration of polaron transport by ultrafast laser-induced coherent phonons

“…Polaron, as a quasiparticle composed of excess carrier dressed by a cloud of virtual phonons (1)(2)(3), intrinsically exists in materials upon charge doping due to strong electron-phonon interactions (EPIs) (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). It plays a central role in determining multifarious physicochemical properties including superconductivity (3,17,18), thermoelectricity (4), and photocatalysis (19)(20)(21). However, the carrier mobility (μ) is also greatly reduced owing to the concurrent propagation of surrounding lattice distortions when polarons are formed, severely hampering the practical applications of associated materials in electronic devices (1,2,5,6).…”