SSCU Student Seminar
Name: Mr. Sirshendu Pathak
Title: Polaron Physics Across Materials: From Inorganic Crystals to Conjugated Polymers
Date & Time: Thursday, 10th September 2026 at 4.00 p.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
A polaron arises when a charge carrier – an electron or a hole – moving through a polarizable crystal lattice locally displaces the surrounding ions or molecules from their equilibrium positions. This creates a self-induced potential well deep enough to trap the carrier into a bound particle-lattice-distortion complex that must be treated as a single coupled system rather than as separate entities. This presentation traces the theoretical development of the polaron concept, beginning with Landau’s original qualitative picture of self-trapping (1933)[1] and Pekar’s subsequent continuum treatment – the Landau-Pekar model (1946)[2] – which established the polaron as a genuinely stable, localized state through its first explicit ground-state energy analysis. It then moves through Fröhlich’s field-theoretic treatment (1954) of long-range electron-phonon coupling, giving rise to spatially extended large polarons, before contrasting this with Holstein’s tight-binding model (1959)[3] for short-range, molecular-crystal polarons. The same Holstein-style Hamiltonian can describe both polarons and excitons[4]. It then connects this theoretical framework to experimental spectroscopy, comparing the optical fingerprints of polarons and excitons in conjugated polymers such as P3HT, and examines chemical doping of P3HT by F4TCNQ – including Schwetz’s model distinguishing free, Coulombically trapped, and bipolaron species via ultrafast spectroscopy.
References:
L. D. Landau, Über die Bewegung der Elektronen in Kristallgitter,1933,Phys. Z. Sowjetunion 3, 664 .
L. D. Landau and S. I. Pekar, Effective mass of a polaron, Zh. Eksp. Teor. Fiz. 18, 419 (1948).
Franchini, C., Reticcioli, M., Setvin, M., & Diebold, U. (2021), Polarons in materials, Nature Reviews Materials, 6(7), 560-586.
Ghosh, R., & Spano, F. C. (2020), Excitons and polarons in organic materials, Accounts of Chemical Research, 53(10), 2201–2211.