100 research outputs found
Analyses of the Polarization Resolved H-alpha Spectra in Various Magnetic Configurations in LHD
Hall coefficient and Hc2 in underdoped LaFeAsO0.95F0.05
The electrical resistivity and Hall coefficient of LaFeAsO0.95F0.05
polycrystalline samples were measured in pulsed magnetic fields up to m0H = 60
T from room temperature to 1.5 K. The resistance of the normal state shows a
negative temperature coefficient (dr/dT < 0) below 70 K for this composition,
indicating insulating ground state in underdoped LaFeAsO system in contrast to
heavily doped compound. The charge carrier density obtained from Hall effect
can be described as constant plus a thermally activated term with an energy gap
DE = 630 K. Upper critical field, Hc2, estimated from resistivity measurements,
exceeds 75 T with zero-field Tc = 26.3 K, suggesting an unconventional nature
for superconductivity.Comment: 12 pages and 4 figure
Anisotropic Electron Velocity Distribution Function in GAMMA10 Tandem Mirror Plasma Analyzed by Means of Plasma Polarization Spectroscopy
Anisotropy of Proton Velocity Distribution Function in Argon Plasma Analyzed by Means of Plasma Polarization Spectroscopy
Self-Consistent Computation of Radiation Transfer in Edge Plasmas Based on Collisional Radiative Model and Neutral Transport Model
The order parameter-entropy relation in some universal classes: experimental evidence
The asymptotic behaviour near phase transitions can be suitably characterized
by the scaling of with , where is
the excess entropy and is the order parameter. As is obtained by
integration of the experimental excess specific heat of the transition , it displays little experimental noise so that the curve versus is better constrained than, say,
versus . The behaviour of for different
universality classes is presented and compared. In all cases, it clearly
deviates from being a constant. The determination of this function can then be
an effective method to distinguish asymptotic critical behaviour. For
comparison, experimental data for three very different systems, Rb2CoF4,
Rb2ZnCl4 and SrTiO3, are analysed under this approach. In SrTiO3, the function
does not deviate within experimental resolution from a straight
line so that, although Q can be fitted with a non mean-field exponent, the data
can be explained by a classical Landau mean-field behaviour. In contrast, the
behaviour of for the antiferromagnetic transition in Rb2CoF4 and
the normal-incommensurate phase transition in Rb2ZCl4 is fully consistent with
the asymptotic critical behaviour of the universality class corresponding to
each case. This analysis supports, therefore, the claim that incommensurate
phase transitions in general, and the ABX compounds in particular, in
contrast with most structural phase transitions, have critical regions large
enough to be observable.Comment: 13 pp. 9 ff. 2 tab. RevTeX. Submitted to J. Phys.: Cond. Matte
Doping dependence of upper critical field and Hall resistivity in LaFeAsO1-xFx
The electrical resistivity (Rxx) and Hall resistivity (Rxy) of LaFeAsO1-xFx
have been measured over a wide fluorine doping range 0 =< x =< 0.14 using 60 T
pulsed magnets. While the superconducting phase diagram (Tc, x) displays the
classic dome-shaped structure, we find that the resistive upper critical field
(Hc2) increases monotonically with decreasing fluorine concentration, with the
largest Hc2 >= 75 T for x = 0.05. This is reminiscent of the composition
dependence in high-Tc cuprates and might correlate with opening of a pseudo-gap
in the underdoped region. Further, the temperature dependence of Hc2(T) for
superconducting samples can be understood in terms of multi-band
superconductivity. Rxy data for non-superconducting samples show non-linear
field dependence, which is also consistent with a multi-carrier scenario.Comment: 15 pages, 5 figures, Accepted by PR
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