Brainy Quote of the Day

Friday, July 4, 2014

Resistance and Quantum Physics...

Figure 1: As an electron (dark blue) in a metal is deflected by an impurity atom (orange), further scattering of the electron is caused by its fluctuating interactions with the surrounding electrons (light blue). These fluctuations add an intrinsically dynamical contribution to the resistivity of the metal. Credit: see [+] below

A new model shows that quantum fluctuations make a significant contribution to a metal’s low-temperature resistance.

Electrical resistance in metals like copper and silver mainly comes from the scattering of electrons by vibrations in the crystal lattice (phonons). These vibrations die away at low temperatures, which explains why metals become less resistive when you cool them. But a small “residual resistivity” persists at low temperatures because electrons also scatter from impurities, such as a vacancy or an atom of a different species, which are always present in any real metal. So far, the residual resistivity was thought to only depend on the interaction between each electron and the impurities, but a new theory from Vladimir Nazarov and Yia-Chung Chang at the Academia Sinica, Taiwan, and Giovanni Vignale at the University of Missouri in Columbia shows that dynamical interactions between electrons—a many-body effect—also make a distinct contribution in the presence of impurities [1]. Their theory provides the first quantitative description, from first principles, of the resistivity of simple metals at low temperatures. As an example, they show that many-electron effects can explain the measured value of the residual resistivity of aluminum.

One of the oldest theories in condensed-matter physics is that of the conduction of an electrical current through a metal. In Paul Drude’s 1900 classical perspective [2], electrons in a metal are constantly moving in all directions, rather like molecules in a gas, but since their net momentum is zero, so is the current. Applying a voltage between the ends of the conductor creates an electric field that causes the electrons to veer slightly towards the positive end, producing a net current. From time to time, collisions once again randomize the electrons’ directions of motion. The frequency of such collisions determines the metal’s resistance. [+]

In a high-resolution photoemission study of a Mo(110) surface state various contributions to the measured width and energy of the quasiparticle peak are investigated. Electron-phonon coupling, electron-electron interactions and scattering from defects are all identified mechanisms responsible for the finite lifetime of a valence photo-hole. The electron-phonon induced mass enhancement and rapid change of the photo-hole lifetime near the Fermi level are observed for the first time. [~]

+ American Physical Society Viewpoint:
Quantum Jostling Proves Diverting for Electrons in a Metal
Rex Godby, Department of Physics, University of York, York YO10 5DD, United Kingdom
~ Physics arXiv:
Many-body Effects in Angle-resolved Photoemission: Quasiparticle Energy and Lifetime of a Mo(110) Surface State
T. Valla, A. V. Fedorov, P. D. Johnson, S. L. Hulbert

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