Nernst effect
Encyclopedia
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
where
is the y-component of the electric field that results from the magnetic field's z-component 
and the temperature gradient 
.
The reverse process is known as the Ettingshausen effect and also as the second Nernst-Ettingshausen effect.
energy carriers (for example conduction-band
electron
s 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.
s 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.
Walther Nernst
Walther Hermann Nernst FRS was a German physical chemist and physicist who is known for his theories behind the calculation of chemical affinity as embodied in the third law of thermodynamics, for which he won the 1920 Nobel Prize in chemistry...
and Albert von Ettingshausen
Albert von Ettingshausen
Albert von Ettingshausen was an Austrian physicist.He was professor of physics at Graz University of Technology, where he also taught electrical engineering.Earlier he was an assistant to Ludwig Boltzmann at the University of Graz....
; note "Ettingshausen" is frequently misspelled "Ettinghausen") is a thermoelectric
Thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference...
(or thermomagnetic) phenomenon observed when a sample allowing electrical conduction is subjected to a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
and a temperature gradient normal (perpendicular) to each other. An electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
will be induced normal to both.
This effect is quantified by the Nernst coefficient |N|, 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 temperature gradient .The reverse process is known as the Ettingshausen effect and also as the second Nernst-Ettingshausen effect.
Physical picture
MobileElectron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...
energy carriers (for example conduction-band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s in a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
) will move along temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
gradients due to statistics and the relationship
between temperature and kinetic energy. If there is a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
transversal to the temperature gradient and the carriers are electrically charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
, they experience a force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
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
Semiconductors exhibit the Nernst effect. This has been studied in the 1950s by Krylova, Mochan and many others. In metalMetal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s however, it is almost non-existent. It appears in the vortex phase
Quantum vortex
In physics, a quantum vortex is a topological defect exhibited in superfluids and superconductors. Superfluids and superconductors are states of matter without friction. They exist only at very low temperatures. The existence of these quantum vortices was independently predicted by Richard Feynman...
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
Pseudogap
The term 'pseudogap' was coined by Nevill Mott in 1968 to indicate a minimum in the density of states at the Fermi energy, N, resulting from Coulomb repulsion between electrons in the same atom, a bandgap in a disordered material or a combination of these...
, as was first found by Xu et al. Heavy-Fermion
Heavy Fermion
In solid-state physics, heavy fermion materials are a specific type of intermetallic compound, containing elements with 4f or 5f electrons. Electrons, a kind of fermion, found in such materials are sometimes referred to as heavy electrons...
superconductors can show a strong Nernst signal which is likely not due to the vortices, as was found by Bel et al.
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
- Nernst effect on arxiv.org