Using AMRO Quantum Oscillations to Probe the Fermi Surface of Quasi-2d Layered Organic Conductors in Low Temperatures and High Magnetic Fields

Abstract

Organic materials are generally synthesized as single crystals with alternating organic-inorganic layers. This induces a reduced dimensionality, leading to a Quasi-two-dimensional (Q2D) salt, having higher conductivity along the crystal plane. This accounts for the ratio of the inter-plane to in-plane resistance reaching upward to an order of a thousand. The electrical anisotropy is seen at Room Temperature and with temperature change and in the presence of a magnetic field which shows up in magnetoresistance (MR), the sample’s resistance response to a magnetic field. By orienting the sample with respect to the magnetic field, we can study the electrical anisotropy evidenced by quantum oscillations in the resistance in the form of Shubnikov-de Haas (SdH) and angular-dependent magnetoresistance oscillations (AMRO). The differences between the two are: SdH measurements display oscillations at fixed temperature and angle as the magnetic field is swept; whereas, AMRO is observed at fixed temperature and magnetic field as the orientation of the sample (angle) is changed. The AMRO angular changes are two types: polar (θ) and azimuthal (φ). The polar angle θ is defined as the angle between the magnetic field and the normal to the two-dimensional organic cation layer, while the azimuthal angle φ is the direction of the magnetic field’s rotation relative to the a-b plane. With SdH oscillatory data, we can extract meaningful information such as the: effective mass, Dingle temperature, frequency of the electron orbits and FS areas. AMRO data analysis leads to direct probing of the FS surface where we can quantify the Fermi wave vector (kf) and map the shape and warping (if present) of the FS and compare it with predictions from band structure calculations. Of note is the magnetic analog of SdH which is de Haas-van Alphen oscillations which shows up as oscillations in the magnetization. The treatment of these oscillations uses LifshitzKosevich Theory [2,3], which when applied to SdH oscillations is extremely effective. In this paper, we will discuss AMRO oscillations and the formalism of their analysis by measuring the interlayer magnetoresistance in a tilted magnetic field at fixed temperatures. We will provide an example of past data for clarity of our discussion [1].