State Of La0 Research Articles

Investigation of the Transport Mechanism in Doped La-Based Manganite Thin Films by Traveling Wave Method

AbstractThe traveling wave (TW) method has been utilized to investigate the transport mechanism in paramagnetic-insulator state of La0.75Sr0.11Ca0.14MnO3 films. The drift mobility of the films increased from 2.5 × 10−2 cm2/Vs at 310 K to about 9.2 × 10−2 cm2/Vs at 400 K. The Arrhenius behaviors of the conductivity and drift mobility indicate that the transport process in manganites above the Curie temperature is dominated by the thermally assisted hopping of small polarons.

Metalliclike mictomagnetic state in La0.55R0.15Ca0.3MnO3 (R=Y and Ho)

The magnetic and electronic transport properties of the title compounds are systematically studied. Both compounds are found to have similar properties. The magnetic measurements are consistent with the mictomagnetic behavior. An insulator-to-metal transition is observed with decreasing temperature and the low temperature resistivity shows the metalliclike feature. It is proposed that apart from the already identified ferromagnetic metal and spin glass insulator phases, the metalliclike mictomagnetic phase should exist at the boundary area between the two known phases in the universal phase diagram for the manganates.

Hall effect in the vortex state of La2−x Sr x CuO4

We have measured the Hall effect in the vortex state of La2−x Sr x CuO4 single-crystal thin films from the underdoped to the overdoped regime (x=0.1–0.24). A sign change of the Hall effect is found belowT c in the underdoped and slightly overdoped samples, while it is absent in the overdoped samples. This result is consistent with the theoretical prediction based on the time-dependent Ginzburg-Landau equation, which suggests that the sign reversal is related to the electronic state at the Fermi level.

Photophysics of Lanthanide Triple Decker Porphyrin Sandwich Complexes

Ground state and time resolved excited state optical absorption spectra and luminescence spectra are reported for La2(OEP)3, Eu2(OEP)3, and Ce2(OEP)3 (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinate). The porphyrin macrocycles in these molecules are strongly coupled due to their mean separation of ≤3.5 A. The triple deckers show many optical properties analogous to those found for double decker porphyrin sandwich complexes, including features not exhibited by porphyrin monomers. Following excitation, the lowest 1(π,π*) state of La2(OEP)3 decays in ∼10 ps predominantly to the phosphorescent 3(π,π*) state, which lives for ∼10 μs. The lowest 1(π,π*) state of Eu2(OEP)3 also decays rapidly and with high yield to the lowest 3(π,π*) state, which has a rather short lifetime of 630 ps. The lack of luminescence from Eu2(OEP)3 is ascribed to deactivation of the 3(π,π*) state through one or more low-energy ligand-field states of the metal ion. Ce2(OEP)3 is also nonluminescent. Unlike La2(OEP)3 and Eu2(OEP)3, the 1(π,...

Electronic Raman scattering from the hole-spin composite states in La2−xSrxCuO4

Electronic Raman scattering was measured in the insulator, superconductor, and “normal metal” phases of La–xSrxCuO4. When holes are doped, the Alg spectra show non-“normal Fermi liquid” behavior. The imaginary part of the experimentally obtained susceptibility is composed of the ω-proportional part below ω∼T and the weakly ω-dependent part up to over 7000 cm−1. The initial gradient increases, on cooling, as in the case of the marginal Fermi liquid model. The Blg spectra have leading edges of which energies decrease with the increase of doping.

Evidence on the nature of superconductivity in La1.85Ba0.15CuO4from specific heat measurements

Information on the nature of the superconducting state in La1.85Ba0.15CuO4 has been obtained from high-precision differential specific heat measurements on superconducting La1.85Ba0.15CuO4, and non-superconducting La2CuO4 and La1.85Ba0.15Cu0.9Ni0.1O4 samples between 1.5 and 300 K. From the very small jump of 0.07 mJ mol-1 K-2 in C/T at Tc approximately 29 K the authors obtain (dHc/dTc)=33 Oe K-1 and Hc(0)=475 Oe, where Hc is the thermodynamic critical field. A condensation of real-space Bose pairs (e.g. bipolarons) is excluded by the author's results, which indicate that a fraction of around 0.06 of the electrons within kTc of the Fermi surface are in Cooper pairs. The estimated electron mass enhancement (1+ lambda ) with lambda approximately 0.82 is lower than expected for conventional phonon-mediated superconductivity with Tc approximately 29 K and indicates that an alternative, possibly excitonic, pair interaction may be involved. Phonon spectra are determined that are in agreement with theoretical predictions, and evidence is obtained for strong high-temperature anharmonicity. A striking anomaly at 58 K in the specific heat of the superconducting compound may indicate a soft phonon mode.

Nuclear relaxation and impurity magnetism in superconducting La1?c Gd c Al2 and La1?c Ce c Al2

The139La spin-lattice relaxation rate in the normal and superconducting states of La1−c Gd c Al2 and La1−c Ce c Al2 alloys has been studied as a probe of the effect of magnetic impurites on superconducting quasiparticle excitations in these systems. Comparison of the experimental data with the theory of pair breaking by magnetic impurities verifies the predicted broadening of the peak in the spectrum of quasiparticle excitations. The dependence of the relaxation rate on the strength of the coupling between conduction electrons and impurities is not fully resolved in the present experiments.

Emission cross section and fluorescence quenching of Nd3+ lanthanum pentaphosphate

The stimulated emission cross section σ for the transitions 4F3/2→4I9/2,11/2 in NdP5O14 and La0.75Nd0.25P5O14 has been measured at 300 °K. For the strongest emission line at 1.0510 μm the value of σE∥b is 18×10−20 cm2, which is to be compared to the value of 46×10−20 cm2 for Nd : YAG. The fluorescence lifetimes of the 4F3/2 state in La1−xNdxP5O14 have been measured at 300 and 77 °K and were found to be independent of temperature. Based on the measured spectroscopic parameters the performance of LED−pumped La0.75Nd0.25P5O14, NdP5O14, and Nd : YAG have been compared both in the end−pumped and side−pumped configurations. In the end−pumped configuration the pentaphosphate has no advantage over Nd:YAG. In the side−pumped case the threshold for La0.75Nd0.25P5O14 is predicted to be lower than that for Nd:YAG.