The field dependence of interlayer magnetoresistance of the pressurized (to the normal state) layered organic metal $\alpha$-(BEDT-TTF)${}_2$KHg(SCN)${}_4$ is investigated. The high quasi-two-dimensional anisotropy, when the interlayer hopping time is longer than the electron mean-free time and than the cyclotron period, leads to a dimensional crossover and to strong violations of the conventional three-dimensional theory of magnetoresistance. The monotonic field dependence is found to change from the conventional behavior at low magnetic fields to an anomalous one at high fields. The shape of Landau levels, determined from the damping of magnetic quantum oscillations, changes from Lorentzian to Gaussian. This indicates the change of electron dynamics in the disorder potential from the usual coherent three-dimensional regime to a new regime, which can be referred to as weakly coherent.

• Received 6 July 2012

DOI:https://doi.org/10.1103/PhysRevB.86.165125