833 research outputs found
On the destruction of the hidden order in URuSi by a strong magnetic field
We present a study of transport properties of the heavy fermion URuSi
in pulsed magnetic field. The large Nernst response of the hidden order state
is found to be suppressed when the magnetic field exceeds 35 T. The combination
of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi
surface in the temperature-field phase diagram. The zero-field ground state is
a compensated heavy-electron semi-metal, which is destroyed by magnetic field
through a cascade of field-induced transitions. Above 40 T, URuSi
appears to be a polarized heavy fermions metal with a large density of carriers
whose effective mass rapidly decreases with increasing magnetic polarization.Comment: published versio
Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport
We report on the study of the Fermi surface of the electron-doped cuprate
superconductor NdCeCuO by measuring the interlayer
magnetoresistance as a function of the strength and orientation of the applied
magnetic field. We performed experiments in both steady and pulsed magnetic
fields on high-quality single crystals with Ce concentrations of to
0.17. In the overdoped regime of we found both semiclassical
angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas
(SdH) oscillations. The combined AMRO and SdH data clearly show that the
appearance of fast SdH oscillations in strongly overdoped samples is caused by
magnetic breakdown. This observation provides clear evidence for a
reconstructed multiply-connected Fermi surface up to the very end of the
overdoped regime at . The strength of the superlattice potential
responsible for the reconstructed Fermi surface is found to decrease with
increasing doping level and likely vanishes at the same carrier concentration
as superconductivity, suggesting a close relation between translational
symmetry breaking and superconducting pairing. A detailed analysis of the
high-resolution SdH data allowed us to determine the effective cyclotron mass
and Dingle temperature, as well as to estimate the magnetic breakdown field in
the overdoped regime.Comment: 23 pages, 8 figure
Shubnikov-de Haas oscillations in YBa_2Cu_4O_8
We report the observation of Shubnikov-de Haas oscillations in the underdoped
cuprate superconductor YBaCuO (Y124). For field aligned along the
c-axis, the frequency of the oscillations is T, which corresponds
to % of the total area of the first Brillouin zone. The effective
mass of the quasiparticles on this orbit is measured to be times
the free electron mass. Both the frequency and mass are comparable to those
recently observed for ortho-II YBaCuO (Y123-II). We show that
although small Fermi surface pockets may be expected from band structure
calculations in Y123-II, no such pockets are predicted for Y124. Our results
therefore imply that these small pockets are a generic feature of the copper
oxide plane in underdoped cuprates.Comment: v2: Version of paper accepted for publication in Physical Review
Letters. Only minor changes to the text and reference
Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and Pure d-wave BCS Superconductor
The transport of heat and charge in the overdoped cuprate superconductor
Tl_2Ba_2CuO_(6+delta) was measured down to low temperature. In the normal
state, obtained by applying a magnetic field greater than the upper critical
field, the Wiedemann-Franz law is verified to hold perfectly. In the
superconducting state, a large residual linear term is observed in the thermal
conductivity, in quantitative agreement with BCS theory for a d-wave
superconductor. This is compelling evidence that the electrons in overdoped
cuprates form a Fermi liquid, with no indication of spin-charge separation.Comment: 4 pages, 2 figures, published version, title changed, Phys. Rev.
Lett. 89, 147003 (2002
Copolymer template control of gold nanoparticle synthesis via thermal annealing
We present here an original process combining top-down and bottom-up
approaches by annealing a thin gold film evaporated onto a hole template made
by etching a PS-PMMA copolymer film. Such process allows a better control of
the gold nanoparticle size distribution which provides a sharper localized
surface plasmon resonance. This makes such route appealing for sensing
applications since the figure of merit of the Au nanoparticles obtained after
thermal evaporation is more than doubled. Such process could besides allow
tuning the localized surface plasmon resonance by using copolymer with various
molecular weights and thus be attractive for surface enhanced raman
spectroscopy
Competing types of quantum oscillations in the 2D organic conductor (BEDT-TTF)8Hg4Cl12(C6H5Cl)2
Interlayer magnetoconductance of the quasi-two dimensional organic metal
(BEDT-TTF)8Hg4Cl12(C6H5Cl)2 has been investigated in pulsed magnetic fields
extending up to 36 T and in the temperature range from 1.6 to 15 K. A complex
oscillatory spectrum, built on linear combinations of three basic frequencies
only is observed. These basic frequencies arise from the compensated closed
hole and electron orbits and from the two orbits located in between. The field
and temperature dependencies of the amplitude of the various oscillation series
are studied within the framework of the coupled orbits model of Falicov and
Stachowiak. This analysis reveals that these series result from the
contribution of either conventional Shubnikov-de Haas effect (SdH) or quantum
interference (QI), both of them being induced by magnetic breakthrough.
Nevertheless, discrepancies between experimental and calculated parameters
indicate that these phenomena alone cannot account for all of the data. Due to
its low effective mass, one of the QI oscillation series - which corresponds to
the whole first Brillouin zone area - is clearly observed up to 13 K.Comment: 8 pages, 8 figures. To be published in Phys. Rev.
Fermi-surface reconstruction and two-carrier model for the Hall effect in YBa2Cu4O8
Pulsed field measurements of the Hall resistivity and magnetoresistance of
underdoped YBa2Cu4O8 are analyzed self-consistently using a simple model based
on coexisting electron and hole carriers. The resultant mobilities and Hall
numbers are found to vary markedly with temperature. The conductivity of the
hole carriers drops by one order of magnitude below 30 K, explaining the
absence of quantum oscillations from these particular pockets. Meanwhile the
Hall coefficient of the electron carriers becomes strongly negative below 50 K.
The overall quality of the fits not only provides strong evidence for
Fermi-surface reconstruction in Y-based cuprates, it also strongly constrains
the type of reconstruction that might be occurring.Comment: 5 pages, 4 figures, updated after publication in Physical Review B
(Rapid Communication
Binary separation in very thin nematic films: thickness and phase coexistence
The behavior as a function of temperature of very thin films (10 to 200 nm)
of pentylcyanobiphenyl (5CB) on silicon substrates is reported. In the vicinity
of the nematic/isotropic transition we observe a coexistence of two regions of
different thicknesses: thick regions are in the nematic state while thin ones
are in the isotropic state. Moreover, the transition temperature is shifted
downward following a 1/h^2 law (h is the film thickness). Microscope
observations and small angle X-ray scattering allowed us to draw a phase
diagram which is explained in terms of a binary first order phase transition
where thickness plays the role of an order parameter.Comment: 5 pages, 3 figures, submitted to PRL on the 26th of Apri
- …