The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.

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By improving the experimental conditions and extensive data accumulation, we have achieved very high precision in the measurements of the de Haas-van Alphen effect in the underdoped high-temperature superconductor YBa2Cu3O6.5. We find that the main oscillation, so far believed to be single frequency, is composed of three closely spaced frequencies. We attribute this to bilayer splitting and warping of a single quasi-2D Fermi surface, indicating that c axis coherence is restored at low temperature in underdoped cuprates. Our results do not support the existence of a larger frequency of the order of 1650 T reported recently in the same compound [S. E. Sebastian, Nature (London) 454, 200 (2008)].

Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

Shubnikov-de Haas (SdH) oscillations and upper critical magnetic field (Hc2) of the iron-based superconductor FeSe (Tc = 8.6 K) have been studied by tunnel diode oscillatorbased measurements in magnetic fields of up to 55 T and temperatures down to 1.6 K. Several Fourier components enter the SdH oscillations spectrum with frequencies definitely smaller than predicted by band structure calculations indicating band renormalization and reconstruction of the Fermi surface at low temperature, in line with previous ARPES data. The Werthamer-Helfand-Hohenberg model accounts for the temperature dependence of Hc2 for magnetic field applied both parallel (H ab) and perpendicular (H c) to the iron conducting plane, suggesting that one band mainly controls the superconducting properties in magnetic fields despite the multiband nature of the Fermi surface. Whereas Pauli pair breaking is negligible for H c, a Pauli paramagnetic contribution is evidenced for H ab with Maki parameter α = 2.1, corresponding to Pauli field HP = 36.5 T.

Analytical formulae for de Haas-van Alphen (dHvA) oscillations in linear chain of coupled two-dimensional (2D) orbits (Pippard's model) are derived systematically taking into account the chemical potential oscillations in magnetic field. Although corrective terms are observed, basic (α) and magnetic-breakdown-induced (β and 2β − α) orbits can be accounted for by the Lifshits-Kosevich (LK) and Falicov-Stachowiak semiclassical models in the explored field and temperature ranges. In contrast, the "forbidden orbit" β − α amplitude is described by a non-LK equation involving a product of two classical orbit amplitudes. Furthermore, strongly non-monotonic field and temperature dependence may be observed for the second harmonics of basic frequencies such as 2α and the magnetic breakdown orbit β + α, depending on the value of the spin damping factors. These features are in agreement with the dHvA oscillation spectra of the strongly 2D organic metal θ-(ET)4CoBr4(C6H4Cl2).

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AbslraeLIn amorphous melallic alloys inadiated with swift heavy ions, electronic excitation induces atomic displacemenu at the beginning of the irradiation and anisotmpic growth above an incubation Ruence. We provide here an extensive review of our data on amorphous F e s B u (including work that i s already published), as well as a general description of the lopic. Samples were inadiated at various temperatures (20 K, 90 K, 223 K) with a large variety of highonergy (GeV) heavy ions (Ar to U). The atomic rearrangements occuning during irradiation were studied by br dm electrim1 mistan= experiments. The influence of the inadiation geometry as well as of a uniaxial stress applied lo the sample was investigated. The whole set of data is accounted for with a Wohit phenomenological model allowing one U) extracl physical pammeters A description of the ion-target interaction on the basis of the Coulomb explosion mechanism is also provided. 1