New insights on frequency combinations and 'forbidden frequencies' in de Haas-van Alphen spectrum of \k{appa}-(ET) 2 Cu(SCN) 2

TL;DR

This study investigates the complex de Haas-van Alphen oscillation spectrum of ppa-(ET)2Cu(SCN)2, revealing the origins of forbidden frequencies through advanced analytical modeling beyond traditional theories.

Contribution

It provides a detailed analysis of frequency combinations and forbidden frequencies in the oscillation spectrum using second order free energy calculations.

Findings

Identification of linear combinations of orbits in the spectrum

Quantitative explanation of forbidden frequencies

Validation of analytical models beyond Lifshitz-Kosevich theory

Abstract

De Haas-van Alphen oscillations of the organic metal \k{appa}-(ET) 2 Cu(SCN) 2 have been measured up to 55 T at liquid helium temperatures. The Fermi surface of this charge transfer salt is a textbook example of linear chain of orbits coupled by magnetic breakdown. Accordingly, the oscillation spectrum is composed of linear combinations of the frequencies linked to the $\alpha$ and magnetic breakdown-induced $\beta$ orbits. The field and temperature dependence of all the observed Fourier components, in particular the "forbidden frequency" $\beta$ -- $\alpha$ which cannot correspond to a classical orbit, are quantitatively accounted for by analytical calculations based on a second order development of the free energy, i.e. beyond the first order Lifshitz-Kosevich formula.