B.L. Freeman

Measurement of the de Haas-van Alphen effect in YBa2Cu3O6.97 using megagauss fields

Abstract The oscillatory component of the magnetic susceptibility (de Haas-van Alphen effect) has been investigated using a dynamically driven, pulsed 105 T flux compression system. Data are presented for oriented 10 μm diameter Y123 single crystalline powders for fields along the (0 0 1) or c axis. It is concluded from these data that Y123 exhibits a Fermi surface in its normal phase at low temperatures.

Complex microwave conductivity of YBa2Cu3O7 in magnetic fields up to 500 T

Abstract The complex microwave conductivity of thin, oriented YBa 2 Cu 3 O 7 films was measured at 94 GHz in pulsed, ultrahigh-magnetic fields up to 500 T. The c -axis of the film was perpendicular to the magnetic field. We estimate the upper critical field of the film at absolute zero as B c2 (0) = 340 ± 40 T. Dynamics of the transition into a normal state and connection with previous measurements of the reversibility line are discussed.

High-field measurements on YBCO

We have performed resistance measurements on thin films of the high-temperature superconductor YBa2Cu3O7 (YBCO) in applied magnetic fields to above 200 T (2 MegaOersted) at temperatures as low as 2.5 K. The fields are produced by an explosively driven flux-compression system. We can see a particularly clear onset, without replotting the data, of the “hydrodynamic” flow of vortices probably because of the very fast increasing field. The low-temperature “critical field” for the field parallel to the c-axis of the sample is 135 T. Our data in the other direction are still preliminary. We discuss possible interpretation of our results.

Megagauss exploration of Hc2 and vortex dynamics in YBa2Cu3O7−x thin films

Abstract New measurements of the dc resistivity ρ(T,H) of YBa2Cu3O7−x (YBCO) below 20K and in magnetic fields > 100T (> 1 Megagauss) show Hc2 ‖ c-axis is near 140T at low temperature. The onset of hydrodynamic vortex flow is also clearly seen and is in agreement with existing data. We have employed a linear fit of sample voltage vs. dB/dt at low fields to systematically remove inductive coupling from the signal voltage and extract ρ(T,H).

Fermi surface and critical field of YBCO

Abstract We have measured extremal areas of the Fermi surface of YBa2Cu3O6.97 by the de Haas-van Alphen effect and the superconducting critical field Hc2(T) by resistence measurements on epitaxial thin of films YBa2Cu3O7 (both called YBCO). Magnetic fields up to 140T were used in flux compression experiments. We have tentatively identified another piece of the Fermi surface with an area of 22kT, which is larger than expected. By both the de Haas-van Alphen effect and the resistance measurements, Hc2 with the applied magnetic field H parallel to the c axis of the YBCO is near 130 T. For H perpendicular to the c axis Hc2 is of the order of 900 T.

Nonlinear Faraday effect in CdS semiconductor in an ultrahigh magnetic field

A significant nonlinearity in the angle of rotation polarization plane was observed in CdS at wavelengths of 494 in the presence of high magnetic fields (0.5-5 MG). The onset significant nonlinearity also depended on sample temperature. An absorption study with probe wavelength of {approximately} 494 nm revealed an increase in optical transmission associated with a splitting of the conduction band. Dispersion, field and temperature curves indicate a low conduction electron mass m{sub e} = 0.3 m{sub o}. A numerical calculation and interpretation of the observed effects was carried out using band theory. The optical and magnetooptical properties of semiconducting crystals of CdS were studied, reviews of which are presented in [1,2]. This article describes joint American-Russian experiments to study the optical and magnetooptical properties of CdS in ultrahigh fields to {approximately} 7 MG.

MC-1 generator performance with higher-energy explosives

The Russian designed MC-1 ultrahigh magnetic field generator was tested in 5 experiments as part of a joint US-Russian collaboration at Los Alamos National Laboratory in December of 1993. The standard Russian explosive (50/50 RDX/TNT) was replaced with higher-energy-density US explosive, either Comp-B (60/40 RDX/TNT) or PBX-9501. Generator performance with Comp-B was nominally the same as reported for experiments with the slightly lower-energy Russian explosive. The Comp-B experiment produced a measured peak field of 9.4 megagauss. Using PBX-9501, the measured peak field increased to 10.9 megagauss with an appropriate increase in the time derivative of the field. One-dimensional MHD calculations with the Lagrangian code, RAVEN are compared with the experimental results.

Explosively produced megagauss fields and recent solid state applications

Abstract Large magnetic fields may be generated by compression of an initial magnetic flux generated over a large area at relatively low magnetic field into a region of smaller area. Following a discussion of flux compression principles, we discuss megagauss field systems in use at Los Alamos where chemical explosives are used to compress the flux. Their use in some solid state experiments will be discussed briefly, including a planned set of experiments on YBCO to be done jointly with a Russian team, whose aim is to determine the low temperature, critical magnetic field of YBCO.

Low-temperature critical field of YBCO

We have measured the upper critical fieldHC2(T) of YBa2Cu3O7 (YBCO) thin films in magnetic fields up to 140 T forH applied parallel to thec-axis of the film. The critical field in the zero-temperature limit is 138 T, and the temperature dependence does not fit any simple model.

de Haas-van Alphen Effect in YBCO

Measurement of the de Haas-van Alphen effect in YBa{sub 2}Cu{sub 3}O{sub 6.97} in pulsed, magnetic fields peaking at 100 T in powdered material with the field applied along the c-axis reveal two pieces of the Fermi surface. Their cross sections are 0.56 kT (0.054 {angstrom}{sup {minus}2}) and 0.78 kT (0.075 {angstrom}{sup {minus}2}) with effective masses of 2.8 and 4.4 respectively.