# Quantum oscillations of a linear chain of coupled orbits with small effective masses: the organic metal $\theta$-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2 )

## TL;DR

This study investigates quantum oscillations in the organic metal $ heta$-(BETS) 4 CoBr 4, revealing small effective masses and complex oscillation behaviors that are explained through advanced analytical formulas, with some phenomena remaining unexplained.

## Contribution

The paper introduces a second order development model for analyzing dHvA oscillations in a linear chain of coupled orbits, accounting for field and temperature dependence and explaining non-Lifshitz-Kosevich behaviors.

## Key findings

- Fourier components are linear combinations of basic orbit frequencies.
- Small effective masses compared to similar organic metals.
- Model explains dHvA amplitude behaviors but not SdH oscillations.

## Abstract

De Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillations of the organic metal $\theta$-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2) are studied in magnetic fields of up to 55 T at liquid helium temperatures. In line with Fermi surfaces (FS) illustrating the linear chain of coupled orbits, the observed Fourier components are linear combinations of the frequencies linked to the two basic orbits $\alpha$ and $\beta$, which have small effective masses compared to other organic metals with the same FS topology. Analytical formulas based on a second order development of the free energy within the canonical ensemble, not only account for the field and temperature dependence of the dHvA amplitudes but also for their relative values. In addition, strongly non-Lifshitz-Kosevich behaviours are quantitatively interpreted. In contrast, Shubnikov-de Haas oscillations are not accounted for by this model. short title: Quantum oscillations of $\theta$-(BETS) 4 CoBr 4 (C 6 H 4 Cl 2)