Normal state properties of the organic superconductor kappa-(ET)2-copper(NCS)2

The organic superconductors are unusually pure systems which exhibit surprisingly large quantum oscillations due to their Fermi surface topology. The Fermi surface topology of kappa-(ET)2Cu(NCS)2 is a textbook example of a linear magnetic breakdown chain and therefore, it allows one to analyze the magnetic breakdown and quantum interference effect.;To study the normal state properties of this organic superconductor, we measured the magnetoresistance quantum oscillations at magnetic fields up to 50 T, temperatures down to 50 mK and angles up to 50°. The measurements were done using an RF-contactless method, called the TDO method. In the TDO method, the geometry of the rf excitation we use, excites in-plane currents. We measured the in-plane resistivity, which is dominated by quantum oscillations corresponding to the magnetic breakdown orbits.;We studied the variation of the frequencies and of the amplitudes in the quantum oscillations in the magnetoresistance resistance as a function of angle. We found that the magnetic breakdown frequencies follow the expected 1/costheta-law. The magnetic breakdown frequencies vary with the angle due to the change of the cross sectional area of the tubular Fermi surface as the angle with respect to the magnetic field is changed. The amplitude of the oscillations changes due to the spin splitting factor which takes into account the ratio between the spin splitting and the energy spacing of the Landau levels. We show that the amplitude of the magnetic breakdown oscillations have also a 1/costheta behavior and that our data agree with the predictions of the Lifshitz-Kosevich-Shoenberg model.;From the observed magnetic breakdown oscillations, the energy gap which separates the closed and open Fermi surfaces at the boundary can be evaluated. In literature, inconsistent values were reported. In order to understand these differences in the magnetic breakdown field (which is a direct measure of the energy gap) values reported in previous experiments, we developed a new method to extract the magnetic breakdown field. We first filter each frequency and then simultaneously fit the alpha and beta frequency amplitudes using the two dimensional Lifshitz-Kosevich and coupled network models. We studied the behavior of the magnetic breakdown field as a function of angle and conclude that it varies with the angle. In addition, the Dingle temperature is found to be different from one orbit to another. This result is new for kappa-(ET) 2Cu(NCS)2 but it has been reported in the literature for other materials.