For typical three-dimensional metals, the temperature-dependence of the electrical resistivity Ï(T) due to the scattering of electrons by acoustic phonons changes from a high-temperature regime in which Ï â T to a low-temperature regime in which Ï â T5 at a characteristic temperature known as the Debye temperature. For low density electron systems, however, the Fermi surface can be substantially smaller than the size of the Brillouin zone, and only a small fraction of acoustic phonons can scatter off electrons. [1] This results in a new characteristic temperature known as the BlochâGrĂŒneisen temperature that is lower than the Debye temperature. The BlochâGrĂŒneisen temperature is defined as 2ħvskF/kB, where ħ is the Planck constant, vs is the velocity of sound, ħkF is the Fermi momentum, and kB is the Boltzmann constant.
When the temperature is lower than the BlochâGrĂŒneisen temperature, the most energetic thermal phonons have a typical momentum of kBT/vs which is smaller than ħkF, the momentum of the conducting electrons at the Fermi surface. This means that the electrons will only scatter in small angles when they absorb or emit a phonon. In contrast when the temperature is higher than the BlochâGrĂŒneisen temperature, there are thermal phonons of all momenta and in this case electrons will also experience large angle scattering events when they absorb or emit a phonon. In many cases, the BlochâGrĂŒneisen temperature is approximately equal to the Debye temperature (usually written ), which is used in modeling specific heat capacity. [2] However, in particular circumstances these temperatures can be quite different. [3]
The theory was initially put forward by Felix Bloch [4] and Eduard GrĂŒneisen. [5] The BlochâGrĂŒneisen temperature has been observed experimentally in a two-dimensional electron gas [3] and in graphene. [6]
Mathematically, the BlochâGrĂŒneisen model produces a resistivity given by: [2]
.
Here, is a characteristic temperature (typically matching well with the Debye temperature). Under Bloch's original assumptions for simple metals, . [4] For , this can be approximated as dependence. In contrast, the so called BlochâWilson limit, where works better for s-d inter-band scattering, such as with transition metals. [7] The second limit gives at low temperatures. [8] In practice, which model is more applicable depends on the particular material. [9]
For typical three-dimensional metals, the temperature-dependence of the electrical resistivity Ï(T) due to the scattering of electrons by acoustic phonons changes from a high-temperature regime in which Ï â T to a low-temperature regime in which Ï â T5 at a characteristic temperature known as the Debye temperature. For low density electron systems, however, the Fermi surface can be substantially smaller than the size of the Brillouin zone, and only a small fraction of acoustic phonons can scatter off electrons. [1] This results in a new characteristic temperature known as the BlochâGrĂŒneisen temperature that is lower than the Debye temperature. The BlochâGrĂŒneisen temperature is defined as 2ħvskF/kB, where ħ is the Planck constant, vs is the velocity of sound, ħkF is the Fermi momentum, and kB is the Boltzmann constant.
When the temperature is lower than the BlochâGrĂŒneisen temperature, the most energetic thermal phonons have a typical momentum of kBT/vs which is smaller than ħkF, the momentum of the conducting electrons at the Fermi surface. This means that the electrons will only scatter in small angles when they absorb or emit a phonon. In contrast when the temperature is higher than the BlochâGrĂŒneisen temperature, there are thermal phonons of all momenta and in this case electrons will also experience large angle scattering events when they absorb or emit a phonon. In many cases, the BlochâGrĂŒneisen temperature is approximately equal to the Debye temperature (usually written ), which is used in modeling specific heat capacity. [2] However, in particular circumstances these temperatures can be quite different. [3]
The theory was initially put forward by Felix Bloch [4] and Eduard GrĂŒneisen. [5] The BlochâGrĂŒneisen temperature has been observed experimentally in a two-dimensional electron gas [3] and in graphene. [6]
Mathematically, the BlochâGrĂŒneisen model produces a resistivity given by: [2]
.
Here, is a characteristic temperature (typically matching well with the Debye temperature). Under Bloch's original assumptions for simple metals, . [4] For , this can be approximated as dependence. In contrast, the so called BlochâWilson limit, where works better for s-d inter-band scattering, such as with transition metals. [7] The second limit gives at low temperatures. [8] In practice, which model is more applicable depends on the particular material. [9]