Cyclotron radius ($r_c$)

The radius of a charged particle orbit perpendicular to a uniform magnetic field. In a parabolic band $r_c=m^{\ast }{v}_{\perp }/(|q|B)$, or $r_c=\hslash k_F/(e|B|)$ for a Fermi-level electron. Charge sign sets the curvature direction, while the radius uses magnitudes.