[show abstract][hide abstract] ABSTRACT: Using a femtosecond pump-probe optical technique, we measured the time-resolv ed change in reflectivity of three single-layer cuprate samples, including Bi2Sr 2 − x La x CuO 6 + z, La2CuO 4 + y and La 2 − x Sr x CuO4 grown on SrTiO3. We analyze the data in terms of a nonthermal electron relaxation model, and obtain quantitative agreement between the model and the data. The initial electron-electron thermalization process is much longer in the superconducting samples as opposed to the overdoped nonsuperconducting sample, suggesting a bottleneck in electron thermalization process due to the presence of the superconducting gap.
[show abstract][hide abstract] ABSTRACT: We report details of floating zone growth of Strontium ruthenate Sr2RuO4 single crystals near the clean limit, with a high onset Tc∼1.5K. We identify conditions under which pure and defective phases, such as the Ru-precipitate based 3K-phase, form. Electronic properties, X-ray diffraction, electron probe microscopy and superconducting properties help us tailor different growth parameters. We also report the first studies of carrier relaxation time in Sr2RuO4 using optical pump–probe reflectivity measurements down to the femtosecond scale. We find a very long relaxation time at 8K, indicating low disorder and weak carrier-lattice coupling at low temperatures.
Journal of Physics and Chemistry of Solids - J PHYS CHEM SOLIDS. 01/2006; 67(1):525-528.
[show abstract][hide abstract] ABSTRACT: Using femtosecond pump-probe measurements, we present transient optical reflectivity measurements of metallic, superconducting and spin-glass La2−xSrxCuO4 cuprates. The rise time is temperature-independent and resolution-limited (<50 fs) for metallic sample, and is much faster than spin-glass samples (∼200 fs) at all temperatures. A divergence in the electron-lattice relaxation (τR) time with temperature is observed for the metallic samples, but not for spin-glass samples.
[show abstract][hide abstract] ABSTRACT: The microscopic origin of unconventional superconductivity1 is one of the most fascinating questions2–3 in condensed matter physics. In recent years, important questions have been raised about the nature of the normal (metallic, non-superconducting) state above the superconducting critical transition temperature (Tc). In fact, it is now generally agreed4,5 that a better understanding of the nature of the normal state is crucial to our understanding of the microscopic origin of the superconducting state.
[show abstract][hide abstract] ABSTRACT: We used a pump-probe technique to measure the transient change of optical reflectivity of both La2-xSrxCuO4, of various dopings, and slightly underdoped YBa2Cu3O7-x and NdBa2Cu3O7-x thin films. For the La2-xSrxCuO4 films, our data demonstrate the coexistence, in the superconducting state, of two coupled subsystems with different relaxation times and different contributions to the optical reflectivity. One subsystem is associated with the superconducting phase. By contrast, the data from YBa2Cu3O7-x and NdBa2Cu3O7-x shows that the coupling between the two subsystems is weak or absent.
[show abstract][hide abstract] ABSTRACT: In the past, occupational therapists have relied upon either indirect reports of client behavior or outcomes of standardized test paradigms to assess the efficacy of their treatment. The use of direct behavioral observations is proposed as an aid in the sensory integrative therapy process. Utilizing this method allows the therapist to quantify data, to devise and answer specific research questions, and to assess the progress of clients in treatment. Advice is given on how to best establish a behavior taxonomy to meet specific needs of the research or therapy situation. The benefits and drawbacks of computer-assisted direct behavioral observation are examined. It is concluded that computer-assisted direct behavioral observation could and should provide a valuable data collection tool in the occupational therapist's repertoire.
Occupational Therapy in Health Care 01/1987; 4(2):129-36.
[show abstract][hide abstract] ABSTRACT: We present pump-probe optical reflectivity measurements on underdoped, optimally doped and overdoped La2-xSrxCuO4 thin films grown on SrTiO3. We find qualitative changes of the reflectivity with temperature, in particular below and above the superconducting transition temperature. We have measured YBa2Cu3O7-x and NdBa2Cu3O7-y thin films for comparison and present these comparative results. The La2-xSrxCuO4 data indicate the existence of two subsystems within the material. The two subsystems are electronic (or optically active), interact, and they transfer energy between them. We discuss our reasoning on these points. 1. M.L. Schneider et.al., submitted