Charles C. Agosta

Measuring radio frequency properties of materials in pulsed magnetic fields with a tunnel diode oscillator

Tunnel diode oscillators have been used in many types of experiments that measure the properties of materials. We present the details of an apparatus that extend these tunnel diode techniques to measure the properties of materials in pulsed magnetic fields. In the most common version of this method, a sample is placed in the inductor of a small rf tank circuit powered by a tunnel diode and the conductivity, magnetization, or penetration depth is measured. We explain in this article how the sample and configuration of the radio frequency fields determine which property is measured. Our major innovations are to stabilize the tunnel diode oscillator during a magnet pulse by using compensated coils in the tank circuit and the development of two methods, one digital and one analog, to measure the frequency and amplitude shifts in the oscillator during the short (10 s of ms) magnet pulse. We illustrate the power of this new measurement method by showing preliminary results of the superconducting transition and ...

Superconducting properties and Fermi-surface topology of the quasi-two-dimensional organic superconductor λ-(BETS)2GaCl4 (BETS≡bis(ethylene-dithio)tetraselenafulvalene)

The Fermi-surface topology of the organic superconductor λ-(BETS)2GaCl4 has been determined using the Shubnikov-de Haas and magnetic breakdown effects and angle-dependent magnetoresistance oscillations. The former experiments were carried out in pulsed fields of up to 60 T, whereas the latter employed quasistatic fields of up to 30 T. All of these data show that the Fermi-surface topology of λ-(BETS)2GaCl4 is very similar to that of the most heavily studied organic superconductor, κ-(BEDT-TTF)2Cu(NCS)2 (BEDT-TTF≡bis(ethylene-dithio)tetrathiafulvalene), except in one important respect: the interplane transfer integral of λ-(BETS)2GaCl4 is a factor ~5 larger than that of κ-(BEDT-TTF)2Cu(NCS)2. The increased three-dimensionality of λ-(BETS)2GaCl4 is manifested in radio-frequency penetration-depth measurements, which show a clear dimensional crossover in the behaviour of Hc2(T). The radio-frequency measurements have also been used to extract the Labusch parameter determining the fluxoid interactions as a function of temperature, and to map the flux-lattice melting curve.

Direct Observation of Spin-Splitting of the Shubnikov- de Haas Oscillations in a Quasi-Two-Dimensional Organic Conductor (BEDT-TTF)2KHg(SCN)4

A clear splitting in the Shubnikov-de Haas oscillation has been directly observed for the first time in a quasi-two-dimensional (2D) organic conductor (BEDT-TTF) 2 KHg(SCN) 4 . Analysis of the oscillations yields a 2D nature of the cylindrical Fermi surface, corresponding to 16% of the first Brillouin zone, with a small warping along the direction normal to the 2D layer. The condition for observation of spin-splitting and the evolution of the splitting pattern with a tilted magnetic field are discussed.

Superconducting phase diagram and FFLO signature in λ -(BETS) 2 GaCl 4 from rf penetration depth measurements

We report the phase diagram of

Experimental techniques for pulsed magnetic fields

\lambda

Magnetic breakdown in the organic conductor (BEDT-TTF)2KHg(SCN)4

-(BETS)

Analysis of de Haas-van Alphen Oscillations and Band Structure of an Organic Superconductor, θ-(BEDT-TTF)2I3

_2

First-row transition metal complexes of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate)

GaCl

Time-dependent Rayleigh-Bénard convection and instrumental attenuation

_4

Magneto-oscillatory behavior and magnetism in quasi-two-dimensional organic conductors

from rf penetration depth measurements with a tunnel diode oscillator in a pulsed magnetic field. We examined four samples with 1100 field sweeps in a range of angles with the magnetic field parallel and perpendicular to the conducting planes. In the parallel direction,