Sunday, 29 January 2012

Nernst effect From Wikipedia, the free encyclopedia

Nernst effect

From Wikipedia, the free encyclopedia

Thermoelectric effect
Peltierelement 16x16.jpg
Applications[show]

In physics and chemistry, the Nernst Effect (also termed first Nernst–Ettingshausen effect, after Walther Nernst and Albert von Ettingshausen; note "Ettingshausen" is frequently misspelled "Ettinghausen") is a thermoelectric (or thermomagnetic) phenomenon observed when a sample allowing electrical conduction is subjected to a magnetic field and a temperature gradient normal (perpendicular) to each other. An electric field will be induced normal to both.

This effect is quantified by the Nernst coefficient |N|, which is defined to be

|N|=\frac{E_Y/B_Z}{dT/dx}

where EY is the y-component of the electric field that results from the magnetic field's z-component BZ and the temperature gradientdT / dx.

The reverse process is known as the Ettingshausen effect and also as the second Nernst-Ettingshausen effect.

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[edit]Physical picture

Mobile energy carriers (for example conduction-band electrons in a semiconductor) will move along temperature gradients due to statistics and the relationship between temperature and kinetic energy. If there is a magnetic field transversal to the temperature gradient and the carriers are electrically charged, they experience a force perpendicular to their direction of motion (also the direction of the temperature gradient) and to the magnetic field. Thus, a perpendicular electric field is induced.

[edit]Sample types

Semiconductors exhibit the Nernst effect. This has been studied in the 1950s by Krylova, Mochan and many others. In metals however, it is almost non-existent. It appears in the vortex phase of type-II superconductors due to vortex motion. This has been studied by Huebener et al. High-temperature superconductors exhibit the Nernst effect both in the superconducting and in the pseudogap phase, as was first found by Xu et al. Heavy-Fermion superconductors can show a strong Nernst signal which is likely not due to the vortices, as was found by Bel et al.

[edit]See also

[edit]Journal articles

  • R. P. Huebener and A. Seher, "Nernst Effect and Flux Flow in Superconductors. I. Niobium", Web
  • R. P. Huebener and A. Seher, "Nernst Effect and Flux Flow in Superconductors. II. Lead Films", Web
  • V. A. Rowe and R. P. Huebener, "Nernst Effect and Flux Flow in Superconductors. III. Films of Tin and Indium", Web
  • Xu, Z. A.; Ong, N. P.; Wang, Y.; Kakeshita, T.; Uchida, S. (2000). "Vortex-like excitations and the onset of superconducting phase fluctuation in underdoped La2-xSrxCuO4". Nature406 (6795): 486–488. Bibcode 2000Natur.406..486X. doi:10.1038/35020016.
  • Bel, R.; Behnia, K.; Nakajima, Y.; Izawa, K.; Matsuda, Y.; Shishido, H.; Settai, R.; Onuki, Y. (2004). "Giant Nernst Effect in CeCoIn5". Physical Review Letters 92 (21): 217002.arXiv:cond-mat/0311473. Bibcode 2004PhRvL..92u7002B. doi:10.1103/PhysRevLett.92.217002.
  • Krylova, T. V.; Mochan, I. V. (1955). J. Tech. Phys. (USSR) 25: 2119.
  • Nernst effect on arxiv.org

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