In physics and chemistry, the Nernst effect (also termed the first Nernst–Ettingshausen effect, after Walther Nernst and Albert von Ettingshausen) 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 , which is defined to be
where is the y-component of the electric field that results from the magnetic field's z-component and the x-component of the temperature gradient .
The reverse process is known as the Ettingshausen effect and also as the second Nernst–Ettingshausen effect.
Physical picture
Mobile energy carriers (for example conduction-band electrons in a semiconductor) will move along temperature gradients due to statistics[dubious – discuss] and the relationshipbetween 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.
Sample types
The semiconductors exhibit the Nernst effect, as first observed by T. V. Krylova and Mochan in the Soviet Union in 1955.[1][non-primary source needed] In metals however, it is almost non-existent.[citation needed]
Superconductors
Nernst effect appears in the vortex phase of type-II superconductors due to vortex motion.[2][3][4] High-temperature superconductors exhibit the Nernst effect both in the superconducting and in the pseudogap phase.[5] Heavy fermion superconductors can show a strong Nernst signal which is likely not due to the vortices.[6]