Crystal structure, Fermi surface calculations and Shubnikov-de Haas oscillations spectrum of the organic metal $\theta$-(BETS)$_4$HgBr$_4$(C$_6$H$_5$Cl) at low temperature

TL;DR

This study investigates the low-temperature crystal structure and electronic properties of the organic metal heta-(BETS)$_4$HgBr$_4$(C$_6$H$_5$Cl), revealing a complex Fermi surface and Shubnikov-de Haas oscillations that suggest a more intricate electronic behavior than previously predicted.

Contribution

The paper provides detailed low-temperature structural data and experimental Fermi surface analysis, showing deviations from room temperature band structure calculations and proposing possible interactions or phase transitions.

Findings

Fermi surface becomes more complex at low temperature

Eight Shubnikov-de Haas frequencies observed up to 54 T

Fermi surface may involve interactions between layers or additional phase transitions

Abstract

The organic metal \theta$-(BETS)$_4$HgBr$_4$(C$_6$H$_5$Cl) is known to undergo a phase transition as the temperature is lowered down to about 240 K. X-ray data obtained at 200 K indicate a corresponding modification of the crystal structure, the symmetry of which is lowered from quadratic to monoclinic. In addition, two different types of cation layers are observed in the unit cell. The Fermi surface (FS), which can be regarded as a network of compensated electron and hole orbits according to band structure calculations at room temperature, turns to a set of two alternating linear chains of orbits at low temperature. The field and temperature dependence of the Shubnikov-de Haas oscillations spectrum have been studied up to 54 T. Eight frequencies are observed which, in any case, points to a FS much more complex than predicted by band structure calculations at room temperature, even though some of the observed Fourier components might be ascribed to magnetic breakdown or frequency mixing. The obtained spectrum could result from either an interaction between the FS's linked to each of the two cation layers or to an eventual additional phase transition in the temperature range below 200 K.