Quasiparticle relaxation dynamics in cuprates and lifetimes of low-energy states: Femtosecond data from underdoped to overdoped YBCO and mercury compounds

We show that low-energy spectral features in the cuprates can be separated into different components by the measurement of the recombination dynamics of different low-energy excitations in real-time using femtosecond laser spectroscopy. Quasiparticle (QP) recombination across the gap and intra-gap localized state relaxation processes exhibit qualitatively different time- and temperature-dependences. The relaxation measurements also show the existence of two distinct coexisting energy gaps near optimum doping and in the overdoped region, one more or less temperature independent (which exists above and below Tc) and one which closes at Tc in a mean-field like fashion. Thus systematic studies of QP recombination as a function of doping and temperature suggest that the ground state of the cuprates is a mixed Boson-Fermion system with localised states present over the entire region of the phase diagram.Comment: 4 pages, acepted for publication in Physica C, invited paper given at M2S, Feb. 20 - 25, 2000, Houston, US

Quasiparticle dynamics and gap structure in Hg1223 investigated with femtosecond spectroscopy

Measurements of the temperature dependence of the quasiparticle (QP) dynamics in Hg1223 with femtosecond time-resolved optical spectroscopy are reported. From the temperature dependence of the amplitude of the photoinduced reflection, the existence of two gaps is deduced, one temperature dependent Dc that closes at Tc, and another temperature independent ''pseudogap'' Dp. The zero-temperature magnitudes of the two gaps are Dc/kTc = 6 +/- 0.5 and Dp/kTc = 6.4 +/- 0.5 respectively. The quasiparticle lifetime is found to exhibit a divergence as T -> Tc from below, which is attributed to the existence of a superconducting gap which closes at Tc. Above Tc the relaxation time is longer than expected for metallic relaxation, which is attributed to the presence of the ''pseudogap''. The QP relaxation time is found to increase significantly at low temperatures. This behavior is explained assuming that at low temperatures the relaxation of photoexcited quasiparticles is governed by a bi-particle recombination process.Comment: accepted for publication in Phys.Rev.

Thermal diffusion of indium in perylenetetracarboxylic dianhydride

Current-voltage (I-V) characteristic measurements of Ag/3,4,9,10-Perylenetetracarboxylic Dianhydride/In/Si(001) heterostructures demonstrate that when the structure temperature approaches the In melting point the I-V characteristic changes from rectifying to Ohmic and the current amplitude increases by several orders of magnitude. The synchrotron radiation photoemission investigation of the 3,4,9,10-Perylenetetracarboxylic Dianhydride (PTCDA) layers of the same thickness grown on In in the same temperature range show strong In diffusion throughout the PTCDA layers as thick as 1 $\mu$m. The In$_{4}$PTCDA coordination compound was not observed on the PTCDA surface and it appears to be limited to the region near the In/PTCDA interface [1]

Mechanical Stabilization Effect of Water on a Membrane-like System

The penetration resistance of a prototypical model-membrane system (HS-(CH2)(11)-OH self-assembled monolayer (SAM) on Au(111)) to the tip of an atomic force microscope (AFM) is investigated in the presence of different solvents. The compressibility (i.e., height vs tip load) of the HS-(CH2)(11)-OH SAM is studied differentially, with respect to a reference structure. The reference consists of hydrophobic alkylthiol molecules (HS-(CH2)(17)-CH3) embedded as nanosized patches into the hydrophilic SAM by nanografting, an AFM-assisted nanolithography technique. We find that the penetration resistance of the hydrophilic SAM depends on the nature of the solvent and is much higher in the presence of water than in 2-butanol. In contrast, no solvent-dependent effect is observed in the case of hydrophobic SAMs. We argue that the mechanical resistance of the hydroxyl-terminated SAM is a consequence of the structural order of the solvent-SAM interface, as suggested by our molecular dynamics simulations. The simulations show that in the presence of 2-butanol the polar head groups of the HS-(CH2)(11)-OH SAM, which bind only weakly to the solvent molecules, try to bind to each other, disrupting the local order at the interface. On the contrary, in the presence of water the polar head groups bind preferentially to the solvent that, in turn, mediates the release of the surface strain, leading to a more ordered interface. We suggest that the mechanical stabilization effect induced by water may be responsible for the stability of even more complex, real membrane system

Modulation of Activity of Known Cytotoxic Ruthenium(III) Compound (KP418) with Hampered Transmembrane Transport in Electrochemotherapy In Vitro and In Vivo

To increase electrochemotherapy (ECT) applicability, the effectiveness of new drugs is being tested in combination with electroporation. Among them two ruthenium(III) compounds, (imH)[trans-RuCl4(im)(DMSO-S)] (NAMI-A) and Na[trans-RuCl4(ind)2] (KP1339), proved to possess increased antitumor effectiveness when combined with electroporation. The objective of our experimental work was to determine influence of electroporation on the cytotoxic and antitumor effect of a ruthenium(III) compound with hampered transmembrane transport, (imH)[trans-RuCl4(im)2] (KP418) in vitro and in vivo and to determine changes in metastatic potential of cells after ECT with KP418 in vitro. In addition, platinum compound cisplatin (CDDP) and ruthenium(III) compound NAMI-A were included in the experiments as reference compounds. Our results show that electroporation leads to increased cellular accumulation and cytotoxicity of KP418 in murine melanoma cell lines with low and high metastatic potential, B16-F1 and B16-F10, but not in murine fibrosarcoma cell line SA-1 in vitro which is probably due to variable effectiveness of ECT in different cell lines and tumors. Electroporation does not potentiate the cytotoxicity of KP418 as prominently as the cytotoxicity of CDDP. We also showed that the metastatic potential of cells which survived ECT with KP418 or NAMI-A does not change in vitro: resistance to detachment, invasiveness, and re-adhesion of cells after ECT is not affected. Experiments in murine tumor models B16-F1 and SA-1 showed that ECT with KP418 does not have any antitumor effect while ECT with CDDP induces significant dose-dependent tumor growth delay in the two tumor models used in vivo