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Photoinduced IR absorption was measured in undoped (LaMn)1−δO3 and (NdMn)1−δO3. We observe broadening and a ∼44% increase of the midinfrared anti-Jahn–Teller polaron peak energy when La3+ is replaced with smaller Nd3+. The absence of any concurent large frequency shifts of the observed PI phonon bleaching peaks and the Brillouin-zone-center internal perovskite phonon modes measured by Raman and infrared spectroscopy indicate that the polaron peak energy shift is mainly a consequence of an increase of the electron phonon coupling constant with decreasing ionic radius 〈 rA〉 on the perovskite A site. This indicates that the dynamical lattice effects strongly contribute to the electronic band narrowing with decreasing 〈 rA〉 in doped giant magnetoresistance manganites. [ABSTRACT FROM AUTHOR]

Femtosecond pump probe experiments are reported on quasiparticle relaxation and recombination in YBa2Cu4O8 as a function of temperature and polarization. We compare our results with the data obtained on YBa2Cu3O7−δ and show that similar two-component relaxation is present in both cases. A strong polarization anisotropy of the picosecond response is observed below Tc and interpreted with the aid of a simple model which considers the anisotropy of the probe transition matrix elements. [ABSTRACT FROM AUTHOR]

Time-resoived optical relaxation measurements on time scales from 10-13 to 10-8 s as a function of energy (0.8–3 eV) and temperature give evidence for the existence of two different carrier relaxation processes, indicating the presence of two distinct electronic subsystems in the normal state in high-temperature superconductors, one exhibiting band-like relaxation properties and the other those of localized, polaronic states. Both components of the electrodynamic response exhibit significant changes at T c , indicating that both carrier types may be involved in superconductivity. The experiments also show that both polarons and band-like carriers exist predominantly in the CuO planes, with an out-of-plane component of the order of 10–20% which is close to the experimentally observed occupancy ratio of holes of O ions of the CuO5 pyramids. Spectrally, the superconducting condensate is also found to be coupled to two distinct components in frequency (for both carriers): one below 0.1 eV and one in the range 1.5-2 eV, but with different anisotropies. A natural explanation of these datas is that the two types of carriers correspond to the two phases suggested by the structural data and as such present the first direct evidence of two-component superconductivity. The underdoped sample data can be interpreted as evidence of pre-formed pairs above T c . [ABSTRACT FROM AUTHOR]

We report a new feature in the photoresponse signal of current-biased YBCO microstructures on very long, us time scales. Negative voltage transient spreading to beyond 30 Μs after excitation by much shorter laser pulses has been observed, and detailed and careful analysis show conclusively that this cannot be explained by any kind of direct bolometric mechanism. We therefore propose a nonbolometric kinetic inductance mechanism as the origin of this response, where the relaxation of the photoexcited quasiparticles through localized states near E F takes place. This mechanism is entirely consistent with our recent observations using femtosecond time-resolved spectroscopy. [ABSTRACT FROM AUTHOR]