451 research outputs found
Tunneling driven tilt modes of the O octahedra in La{2-x}Sr{x}CuO{4}: strong dependence on doping
The anelastic spectrum of La{2-x}Sr{x}CuO{4} (x = 0, 0.008, 0.019, 0.032) has
been measured down to 1.5 K, in order to see the effect of doping on the
intrinsic lattice fluctuations already found in stoichiometric La{2}CuO{4}, and
identified with tunneling driven tilt modes of the O octahedra. Slight doping
with Sr causes a drastic increase of the transition rates and relaxation
strength of the tunneling systems. The influence of doping on the relaxation
rate is interpreted in terms of direct coupling between between the tilts of
the octahedra and the hole excitations. However, the observed fast dependence
of the rate on temperature cannot be explained in terms of the ususal models of
coupling between a tunneling system and the conduction electrons.Comment: LaTeX, 5 figures in a single PostScript file, submitted to Phys. Rev.
Anelastic relaxation process of polaronic origin in La{2-x}Sr{x}CuO{4}: interaction between the charge stripes and pinning centers
The evolution of an anelastic relaxation process occurring around 80 K in
La{2-x}Sr{x}CuO{4} at a measuring frequency of ~1 kHz has been followed from x
= 0.0075 to the overdoped region, x = 0.2, where it disappears. The dependence
of the peak intensity on doping is consistent with a polaronic mechanism,
identified with the disordered charge stripes overcoming pinning centers. A
marked decrease of the peak amplitude occurs at x > 0.045, the same doping
range where a change of the stripe order from parallel to diagonal with respect
to the Cu-O bonds has been observed by neutron diffraction. Both the energy
barrier and peak amplitude also exhibit a rise near x = 1/8.Comment: 5 pages, 4 figure
Anelastic relaxation and La NQR in LaSrCuO around the critical Sr content x=0.02
Anelastic relaxation and La NQR relaxation measurements in
LaSrCuO for Sr content x around 2 and 3 percent, are presented
and discussed in terms of spin and lattice excitations and ordering processes.
It is discussed how the phase diagram of LaSrCuO at the
boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02)
could be more complicate than previous thought, with a transition to a
quasi-long range ordered state at T = 150 K, as indicated by recent neutron
scattering data. On the other hand, the La NQR spectra are compatible
with a transition to a conventional AF phase around T = 50 K, in agreement with
the phase diagram commonly accepted in the literature. In this case the
relaxation data, with a peak of magnetic origin in the relaxation rate around
150 K at 12 MHz and the anelastic counterparts around 80 K in the kHz range,
yield the first evidence in LaSrCuO of freezing involving
simultaneously lattice and spin excitations. This excitation could correspond
to the motion of charged stripes.Comment: 10 pages, 8 figure
Topical nicotinamide for seborrheic dermatitis: an open randomized study.
Background: Treatment of seborrheic dermatitis (SD) includes various options with different success and safety limitations. Objective: To evaluate the efficacy of topical nicotinamide (NCT) in the treatment of SD. Methods: A total of 48 patients with mild to moderate SD of the face were enrolled in the study (36 males and 12 females; age 20-50 years). Patients were randomized into two groups A and B, who were treated once a day with topical administration of NCT 4% cream and with the vehicle without NCT (placebo), respectively. Clinical measures were assessed by erythema, scaling, and infiltration, which were evaluated using a four-point scale 0-3 before starting treatment and after 2, 6, and 12 weeks' therapy. Results: In comparison with baseline, a reduction of 75% of the total score was observed in patients treated with NCT, whereas for placebo-treated patients the reduction was of 35% (p < 0.05). Conclusion: Topical NCT 4% can have a potential for the treatment of SD
Observation of the cluster spin-glass phase in La_{2-x}Sr_{x}CuO_{4} by anelastic spectroscopy
An increase of the acoustic absorption is found in La_{2-x}Sr_{x}CuO_{4} (x =
0.019, 0.03 and 0.06) close to the temperatures at which freezing of the spin
fluctuations in antiferromagnetic-correlated clusters is expected to occur. The
acoustic absorption is attributed to changes of the sizes of the quasi-frozen
clusters induced by the vibration stress through magnetoelastic coupling.Comment: LaTeX, 2 PostScript figures, submitted to Phys. Rev.
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