Millimetre-wave measurements of the bulk magnetoconductivity of anisotropic metals: application to the organic superconductors κ-(BEDT-TTF)₂Cu(NCS)₂and β^''-(BEDT-TTF)₂SF₅CH₂CF₂SO₃(BEDT-TTF≡bis(ethylene-dithio)tetrathiafulvalene)

Abstract

We describe a novel resonant cavity system which allows the bulk magneto-conductivity of single crystals of anisotropic metals to be measured at GHz frequencies. The cavity can be made to rotate in a static magnetic field, permitting detailed studies of the dependence on the magnetic field orientation of the high-frequency magnetoconductivity. In this paper, the apparatus is used to measure the Fermi-surface topology of two organic superconductors; the details revealed are inaccessible to conventional fermiological techniques such as the de Haas-van Alphen effect. In κ-(BEDT-TTF)2Cu(NCS)2, Fermi-surface traversal resonances (FTRs) are observed. The angle dependence of the FTRs shows that the quasi-one-dimensional (Q1D) Fermi sheets of this material possess two distinct corrugations, with corrugation axes making angles of 17.3° and -19.4° with the ka-axis. Such data form important input parameters for current models of superconductivity in the organics, which invoke spin-density-wave-like fluctuations caused by partial nesting of the Q1D Fermi sheets. In β''-(BEDT-TTF)2SF5CH2CF2SO3, cyclotron resonance is observed, along with its second and third harmonics. The detailed angle dependence of the intensities of the various cyclotron harmonics allows the elongation and orientation of the closed section of the Fermi surface to be deduced, and strongly suggests that the interplane transport is coherent in this material. The effective mass deduced from the cyclotron resonance measurements is greater than that determined from magnetic quantum oscillations, in agreement with recent theoretical predictions.

Control of the third dimension in copper-based square-lattice antiferromagnets

“…For single-crystal g-factor anisotropy measurements, a monomoded cavity, resonating at a frequency of around 71 GHz and mounted on a cryogenic goniometer was employed 29 . This allows the crystal to be rotated with respect to the applied magnetic field without thermal cycling.…”

Fermi Surface Study of Quasi-Two-Dimensional Organic Conductors by Magnetooptical Measurements

“…7 and we refer the reader to a series of articles on the cavity perturbation technique. [8][9][10][11][12] The typical sample size used for this study were from 0.25 x 0.5 x 0.1 to 1 x 1 x 0,1 mm 3 and the static magnetic field was applied perpendicular to the conducting plane. The cylindrical cavity was used for this study and the frequencies used are around 58 GHz and 72 GHz whose cavity mode corresponds to TE 011 and TE 012 , respectively.…”

Thermal Activation between Landau Levels in the Organic Superconductorβ′′−(BEDT−TTF)2Nam1, Ardavan2, Symington3 et al. 2001Phys. Rev. Lett.278481View full textAdd to dashboardCite

“…However, Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) measurements reveal that the Q2D cylinder has only one third the expected cross-section [7,8,9]. Angle-dependent magnetoresistance oscillation (AMRO) [8,10] and millimetre-wave magnetoconductivity experiments [11] show that the cross-section of this Q2D pocket resembles an elongated diamond. The same experimental techniques find no evidence for the presence of Q1D Fermi sheets at low temperatures [8,10,11], unlike the situation in other Q2D organic metals [3].…”

“…Angle-dependent magnetoresistance oscillation (AMRO) [8,10] and millimetre-wave magnetoconductivity experiments [11] show that the cross-section of this Q2D pocket resembles an elongated diamond. The same experimental techniques find no evidence for the presence of Q1D Fermi sheets at low temperatures [8,10,11], unlike the situation in other Q2D organic metals [3]. By contrast, in order to explain the observation of a fixed chemical potential µ in the dHvA effect [7], Wosnitza et al proposed Q1D states which have an enormous density of states, exceeding the estimates from bandstructure calculations by at least an order of magnitude [7].…”