Editing Electron cyclotron resonance (section)

== In condensed matter physics ==
Within a solid the mass in the cyclotron frequency equation above is replaced with the [[effective mass (solid-state physics)|effective mass]] tensor <math>m^*</math>.  Cyclotron resonance is therefore a useful technique to measure [[effective mass (solid-state physics)|effective mass]] and [[Fermi surface]] cross-section in solids.  In a sufficiently high magnetic field at low temperature in a relatively pure material
: <math>\begin{align}
         \omega_\text{ce} &> \frac{1}{\tau} \\
  \hbar{\omega}_\text{ce} &> k_\text{B} T \\
\end{align}</math>
where <math>\tau</math> is the carrier scattering lifetime, <math>k_\text{B}</math> is the [[Boltzmann constant]] and <math>T</math> is temperature.  When these conditions are satisfied, an electron will complete its cyclotron orbit without engaging in a collision, at which point it is said to be in a well-defined Landau level.