In order to calculate the dependence of electrical conductivity on the magnetic field, we adopt a semiclassical approach, within the framework of Boltzmann transport theory. Having in mind the case of high-
superconducting cuprates as a case study, our calculation applies to a layered system with tetragonal symmetry (for which we set the lattice spacing to 1), and we specialize to the case of a magnetic field perpendicular to the layers. The conductivity tensor for such a system, in the presence of a transverse magnetic field, is a
matrix such that the two diagonal components are equal to each other, as are the two off-diagonal components. The conductivity tensor is therefore determined only by the two components diagonal and off-diagonal, which we indicate with
and
, respectively. To determine the magnetic field dependence of these two quantities without any a priori assumption on the ratio between the scattering rate and the cyclotron frequency, we rely on Chambers’ solution to the Boltzmann equation [
26]:
where where e is the absolute value of the electron charge,
B is the
z-component of the transverse magnetic field
,
is the magnitude of the electron group velocity
, where
is the electron band dispersion law, while
and
refer instead to the two components of
(we set
). The quantity denoted by
is the volume of the three-dimensional unit cell of the layered system, so according to our units it is simply the inter-layer distance in units of the in-plane lattice spacing. This quantity plays no role in our further calculations. Since our goal is to evaluate how the scattering anisotropy along the Fermi surface can affect the magnetotransport properties of the system, we consider an angle-dependent elastic scattering rate that does not violate the tetragonal symmetry of the system. In particular, we adopt a scattering rate of the same form proposed in Refs. [
13,
25]:
where
denotes the angle that the Fermi surface vector
makes with the positive
x-semiaxis in the first Brillouin zone. In our analysis, we are not going to study the behavior of the conductivity as a function of temperature, therefore we do not need to separate the elastic and the inelastic components in the scattering rates
and
. The dependence on the magnetic field in equations (
1) comes into play through the time evolution of the vector
. This time evolution is governed the standard equation of motion for an electron in a uniform electric and magnetic field:
where
,
and
lie on the lattice plane, while
is orthogonal. However, since we are not interested in non-linear effects in the electrostatic field, we can set
at this level. It is worth noting that, according to the system of units we are using, the quantity
is dimensionless. In fact, the magnetic field
B can be conveniently expressed in units of
(where
a is the in-plane lattice spacing), which is equal to
in our units. We define the magnetoresistance such that it vanishes at
: