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Abstract:

We report magnetic-field-orientation dependent de Haas-van Alphen (dHvA) experiments on the filled skutterudites PrOs4As12 and LaOs4As12. The Fermi surfaces of the compounds are very similar and in reasonable agreement with bandstructure calculations for LaOs4As12 on a PrOs4As12 lattice. This suggests that the 4f electrons are essentially localized in the paramagnetic phase of PrOs4As12. Whilst the properties of LaOs4As12 suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations cause dHvA beat frequencies and field-dependent quasiparticle masses in PrOs4As12. © 2007 Elsevier B.V. All rights reserved.

Abstract:

We have developed an analytical model of angle-dependent magnetoresistance oscillations (AMROs) in a quasi-two-dimensional metal in which magnetic breakdown occurs. The model takes account of all the contributions from quasiparticles undergoing both magnetic breakdown and Bragg reflection at each junction and allows extremely efficient simulation of data which can be compared with recent experimental results on the organic metal κ- (BEDT-TTF)2 Cu (NCS)2. AMROs resulting from both closed and open orbits emerge naturally at low field, and the model enables the transition to breakdown-AMROs with increasing field to be described in detail. © 2008 The American Physical Society.

Abstract:

We present experimental evidence for a hitherto unconfirmed type of angle-dependent magnetoresistance oscillation caused by magnetic breakdown. The effect was observed in the organic superconductor κ- (BEDT-TTF)2 Cu (NCS)2 using hydrostatic pressures of up to 9.8 kbar and magnetic fields of up to 33 T. In addition, we show that similar oscillations are revealed in ambient-pressure measurements, provided that the Shubnikov-de Haas oscillations are suppressed either by elevated temperatures or filtering of the data. These results provide a compelling validation of Pippard's semiclassical picture of magnetic breakdown. © 2007 The American Physical Society.

Abstract:

Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs4AS12 and LaOs4AS12 using magnetic fields of up to 40 T. Several peaks are observed in the low-field susceptibility of PrOs4AS 12, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs4AS12 in its PMM phase and LaOs4AS 12 are very similar. In addition, they are in reasonable agreement with the predictions of bandstructure calculations for LaOs4AS 12 on the PrOs4AS12 lattice. Both observations suggest that the Pr 4f electrons contribute little to the number of itinerant quasiparticles in the PMM phase. However, while the properties of LaOs 4AS12 suggest a conventional nonmagnetic Fermi liquid, the effects of direct exchange and electron correlations are detected in the PMM phase of PrOs4AS12. For example, the quasiparticle effective masses in PrOs4AS12 are found to decrease with increasing field, probably reflecting the gradual suppression of magnetic fluctuations associated with proximity to the low-temperature, low-field antiferromagnetic state. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Abstract:

The interlayer magnetoresistance rho(zz) of the organic metal kappa-(BEDT-TTF)(2)Cu(NCS)(2) is studied in fields of up to 45 T and at temperatures T from 0.5 to 30 K. The peak in rho(zz) seen in in-plane fields, a definitive signature of interlayer coherence, remains to Ts exceeding the Anderson criterion for incoherent transport by a factor approximately 30. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the T dependence of the scattering rate tau(-1). The results suggest that tau(-1) does not vary strongly over the Fermi surface, and that it has a T(2) dependence due to electron-electron scattering.