Publication

Evidence of Large Polarons in Photoemission Band Mapping of the Perovskite Semiconductor CsPbBr3

Majed Chergui, Nicola Marzari, Marco Grioni, Nicola Colonna, Michele Puppin, Matthias Wolf, Alberto Crepaldi, Gianmarco Gatti, Serhii Polishchuk, Thomas Roland Barillot, Riccardo De Gennaro
2020
Journal Articles

Abstract

Lead-halide perovskite (LHP) semiconductors are emergent optoelectronic materials with outstanding transport properties which are not yet fully understood. We find signatures of large polaron formation in the electronic structure of the inorganic LHP CsPbBr3 by means of angle-resolved photoelectron spectroscopy. The experimental valence band dispersion shows a hole effective mass of 0.26 +/- 0.02 m(e), 50% heavier than the bare mass m(0) = 0.17 m(e) predicted by density functional theory. Calculations of the electron-phonon coupling indicate that phonon dressing of the carriers mainly occurs via distortions of the Pb-Br bond with a Frohlich coupling parameter alpha = 1.81. A good agreement with our experimental data is obtained within the Feynman polaron model, validating a viable theoretical method to predict the carrier effective mass of LHPs ab initio.

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https://infoscience.epfl.ch/entities/publication/883d567c-d1f3-4648-98f3-dcf0d98a0a38

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Abstract

Official source

https://infoscience.epfl.ch/entities/publication/883d567c-d1f3-4648-98f3-dcf0d98a0a38

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Related concepts (23)

Polaron

A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. The polaron concept was proposed by Lev Landau in 1933 and Solomon Pekar in 1946 to describe an electron moving in a dielectric crystal where the atoms displace from their equilibrium positions to effectively screen the charge of an electron, known as a phonon cloud. This lowers the electron mobility and increases the electron's effective mass.

Effective mass (solid-state physics)

In solid state physics, a particle's effective mass (often denoted ) is the mass that it seems to have when responding to forces, or the mass that it seems to have when interacting with other identical particles in a thermal distribution. One of the results from the band theory of solids is that the movement of particles in a periodic potential, over long distances larger than the lattice spacing, can be very different from their motion in a vacuum.

Electronic band structure

In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called band gaps or forbidden bands). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules.

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