Soviet physicist Igor Tamm introduced the concept of phonons in 1932, as a collective excitation of atoms or molecules in condensed matter. These characteristic vibration modes of the crystal lattice can couple to electrons as they travel through a crystal, making them move as if they are heavier and less mobile. A pronounced electron-phonon coupling is known to mediate the formation of so-called polarons, a composite quasiparticle formed of an electron and a phonon cloud. Previous research has shown that polarons have a significantly enhanced effective mass, which can impose fundamental limits on electron mobility in semiconductors (important in, for example, transistors). It has also been suggested that they play an important role in certain unconventional superconducting states.
Diamond is the ideal place to carry out this research, which requires the ability to fabricate high-quality thin-film samples, to transfer these to the measurement chamber without them ever leaving an ultra-high vacuum environment, and then to perform ARPES measurements at carefully chosen photon energies to enable probing the relevant electronic states of interest.”
The team discovered two distinct regimes of how the electrons behave in differently-doped EuO samples. At lower doping concentrations, the measurements showed how distinct loss-features could be observed separated by the energy of a known phonon mode of this material. This points to a phonon polaron state, similar to that observed in other materials with strong electron-phonon coupling.
Diamond Light Source is the UK's national synchrotron science facility, located at the Harwell Science and Innovation Campus in Oxfordshire.
Copyright © 2020 Diamond Light Source
Diamond Light Source Ltd
Harwell Science & Innovation Campus
Diamond Light Source® and the Diamond logo are registered trademarks of Diamond Light Source Ltd