The upper superconducting critical magnetic field of the polymer (SN)x was investigated as a function of temperature and crystallographic orientation, over the range 40 mK-1K using accurately steerable magnetic fields up to 11 kG. The values are slightly sample dependent and at T=0 the authors estimate that for the best sample Hc2 approximately=8.5 kG for H//b, the fibre axis, with Hc2 approximately=900 G for H//a* and Hc2 approximately=1100 G for H//c. The variations between samples are ascribed to the (100) twinning shown by all samples. This takes place on a microscopic scale, as is shown by X-ray measurements, and is probably associated with the fibrous structure. The X-ray measurements give a mean fibre size of about 50 AA. The temperature dependence Hc2//(T) agrees with the predictions of the da Silva-Gyorffy model (1979) for an independent anisotropic fibre, but Hc2 perpendicular to (T) is quite different from that predicted for this model.
The magnetoreflection spectrum of antimony has been measured for circularly polarized radiation. The lowest energy peak for the 0.149 eV gap is observed to split into four components, two for each polarization. These show considerable deviations from the Cohen-Lax two-band model, and values of mc=0.240 m0, gc=99 for the conduction band, and mv=0.0164 m0, gv=76 for the valence band, have been inferred from a generalization of the Maltz selection rules.
Measurements were made of the fluctuation conductivity and critical magnetic fields of the superconducting polymer (SN)x as a function of temperature and magnetic field. The temperature dependence of the fluctuation conductivity and the critical field parallel to the fibre axis agree with the theory given by da Silva and Gyorffy (1978) for independent anisotropic metal fibres, but not with their model of a bulk anisotropic superconductor. That of the perpendicular critical field fits neither model.
A detailed and accurate study of the de Haas-van Alphen effect and Fermi surface of arsenic has been made by a vector-modulation technique. We find two sets of Fermi surfaces which together give the required volume compensation. The first set contains three closed, centrosymmetric pockets ($\ensuremath{\beta}$ in our notation) which have a tilt angle (for the minimum area) of 86.4\ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{} from the trigonal axis. Their total volume is found to be (2.12\ifmmode\pm\else\textpm\fi{}0.01) \ifmmode\times\else\texttimes\fi{} ${10}^{20}$ carriers/${\mathrm{cm}}^{3}$. The other set forms a single multiply connected surface of symmetry $\overline{3}m$ and consists of six $\ensuremath{\alpha}$ pockets (the Berlincourt carriers) which have a tilt angle of 37.25\ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{}, and which are connected together by six long thin necks with a tilt of -9.6\ifmmode\pm\else\textpm\fi{}0.1\ifmmode^\circ\else\textdegree\fi{}. This is in excellent agreement with the recent pseudopotential calculation by Lin and Falicov if the $\ensuremath{\beta}$ pockets are due to electrons at $L$ and the multiply connected surface to holes around $T$. The multiplicities of the pockets are deduced from the experimental data and are supported by the consequent satisfactory agreement with the observed electronic specific heat.
Abstract Preliminary results of high field de Haas-van Alphen experiments in aluminium are presented. New fast periods have been found and the corresponding Fermi surface areas agree with those predicted in the nearly free electron model. The data confirm both the general shape of the second zone surface and the topology of the third zone surface.
A careful study, mainly by the torque method, of the low-field de Haas-van Alphen effect in thallium enables the new long period data to be interpreted in terms of an additional small dumb-bell-shaped Fermi surface with symmetry 6m2 at H in the fifth zone. This is at variance with the ROPW calculation of the band structure but preliminary pseudopotential calculations which were made using the Heine-Abarenkov model potential appear to remove the discrepancy. Additional very long periods of approximately 2*10-5G-1 were observed and are assigned to small hole pockets at M in the third zone or to electrons on the Gamma M line in the fourth zone.
We have observed both geometric and open-orbit resonances in the ultrasonic attenuation in thallium at frequencies up to 460 Mc/sec. Sound was propagated in the [0001], [11\ifmmode\bar\else\textasciimacron\fi{}20], and [10\ifmmode\bar\else\textasciimacron\fi{}10] directions and extremal k vectors in the planes perpendicular to these propagation directions were measured. The measured k vectors agree well with the calculated values of Soven for the major pieces of the Fermi surface. We also observed an open-orbit resonance and several subharmonics for $\stackrel{^}{q}$ parallel to [0001] and $\stackrel{^}{H}$ parallel to [11\ifmmode\bar\else\textasciimacron\fi{}20]. This results from magnetic breakdown between zones 3 and 4 in the vicinity of the $\mathrm{AL}$ line. No open orbits along the $c$ axis were observed, probably indicating that the fourth-zone electron surface does not contact the $\mathrm{ALH}$ plane.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
