Nonanalytical magnetoresistance, the third angular effect, and a method to investigate Fermi surfaces in quasi-two-dimensional conductors

We demonstrate that transverse magnetoresistance is a nonanalytical function of the magnetic field, ρperpendicular(H)∼|H|1/2, if a magnetic field is parallel to the plane of anisotropy and normal to the Fermi surface at an inflection point in a quasi-two-dimensional (Q2D) conductor. The so-called open-quotes third angular effect,close quotes recently discovered in organic conductors (TMTSF)2X (X=ClO4,PF6) and (DMET)2I3, is interpreted in terms of the existence of an inflection point on their Fermi surfaces. Nonanalytical magnetoresistance is predicted to appear when the magnetic field is applied at the open-quotes third magic angles,close quotes Θ=±Θc. It is also shown that at arbitrary directions of the in-plane magnetic field the magnetoresistance does not depend on relaxation time and obeys the law ρperpendicular(H)∼A|H| with factor A being a function of local characteristics of a Q2D Fermi surface. The above-mentioned phenomena provide useful methods to investigate Fermi surfaces in strongly anisotropic Q2D conductors including organic and high-Tc superconductors. copyright 1997 The American Physical Society