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 formula_1, which is defined to be
formula_2
where formula_3 is the y-component of the electric field that results from the magnetic field's z-component formula_4 and the x-component of the temperature gradient formula_5.
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 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.
Sample types.
The semiconductors exhibit the Nernst effect, as first observed by T. V. Krylova and Mochan in the Soviet Union in 1955. In metals however, it is almost non-existent.
Superconductors.
Nernst effect appears in the vortex phase of type-II superconductors due to vortex motion. High-temperature superconductors exhibit the Nernst effect both in the superconducting and in the pseudogap phase. Heavy fermion superconductors can show a strong Nernst signal which is likely not due to the vortices.