De Haas–van Alphen and chemical potential oscillations in the magnetic-breakdown quasi-two-dimensional organic conductorκ−(BEDT−TTF)2Cu(NCS)2

Abstract

We present an analytical theory for the de Haas--van Alphen (dHvA) oscillations in layered organic conductors such as $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}{(\mathrm{NCS})}_{2}$ which takes into account the magnetic breakdown and the chemical potential oscillations. For this purpose we have generalized our theory for the chemical potential oscillations in layered conductors [V.M. Gvozdikov, A.G.M. Jansen, D.I. Pesin, I.D. Vagner, and P. Wyder, Phys. Rev. B 68, 155107 (2003)] to the case of an arbitrary electron dispersion within the layers. Such an approach gives a better agreement with an experimental data for $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}{(\mathrm{NCS})}_{2}$ salt than that taking account of the magnetic breakdown (MB) only [V.M. Gvozdikov, Yu.V. Pershin, E. Steep, A.G.M. Jansen, and P. Wyder, Phys. Rev. B 65, 165102 (2002)]. The magnetization oscillation patterns and the peaks in the fast Fourier transforms (FFT's) are studied in different combinations of the stochastic and coherent MB regimes with and without the chemical potential oscillations. It is shown that that the chemical potential oscillations in the coherent and stochastic MB regimes do not affect the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ peaks, but change the amplitudes of the higher harmonics and satellites around the $\ensuremath{\beta}$ peak. In the FFT spectrum of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}{(\mathrm{NCS})}_{2}$ two satellites are resolved: $\ensuremath{\beta}\ensuremath{-}\ensuremath{\alpha}$ (the so called ``forbidden'' peak) and $\ensuremath{\beta}+\ensuremath{\alpha}$. In the stochastic MB regime all satellites are depressed. In the coherent MB regime with fixed chemical potential they are higher and have equal amplitudes. Only in the coherent MB regime with oscillating chemical potential the ``forbidden'' peak $\ensuremath{\beta}\ensuremath{-}\ensuremath{\alpha}$ becomes larger than the satellite $\ensuremath{\beta}+\ensuremath{\alpha}$ and the calculated FFT spectrum conforms with the FFT spectrum of the dHvA signal of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}{(\mathrm{NCS})}_{2}$.