62 research outputs found
Pairing mechanism of high-temperature superconductivity: Experimental constraints
Developing a theory of high-temperature superconductivity in copper oxides is
one of the outstanding problems in physics. It is a challenge that has defeated
theoretical physicists for more than twenty years. Attempts to understand this
problem are hindered by the subtle interplay among a few mechanisms and the
presence of several nearly degenerate and competing phases in these systems.
Here we present some crucial experiments that place essential constraints on
the pairing mechanism of high-temperature superconductivity. The observed
unconventional oxygenisotope effects in cuprates have clearly shown strong
electron-phonon interactions and the existence of polarons and/or bipolarons.
Angle-resolved photoemission and tunneling spectra have provided direct
evidence for strong coupling to multiple-phonon modes. In contrast, these
spectra do not show strong coupling features expected for magnetic resonance
modes. Angle-resolved photoemission spectra and the oxygen-isotope effect on
the antiferromagnetic exchange energy J in undoped parent compounds
consistently show that the polaron binding energy is about 2 eV, which is over
one order of magnitude larger than J = 0.14 eV. The normal-state
spin-susceptibility data of holedoped cuprates indicate that intersite
bipolarons are the dominant charge carriers in the underdoped region while the
component of Fermi-liquid-like polarons is dominant in the overdoped region.
All the experiments to test the gap or order-parameter symmetry consistently
demonstrate that the intrinsic gap (pairing) symmetry for the Fermi-liquid-like
component is anisotropic s-wave and the order-parameter symmetry of the
Bose-Einstein condensation of bipolarons is d-wave.Comment: 12 pages, 5 figures, invited comment by Physica Script
Even-parity autoionizing states in the extreme-ultraviolet photoabsorption spectra of Mg, Al⁺, and Si²⁺
The dual-laser-produced plasma (DLP) photoabsorption technique has been used to study 2p→3s excitations in the isoelectronic species Mg, Al+, and Si2+ prepared in the excited configuration 2p63s3p. The autoionizing upper states belong to the 2p53s23p even-parity configuration. The versatility of the technique is demonstrated through a careful combination of space- and time-resolved photoabsorption scans. Plasma conditions optimized for the observation of the inaccessible parity regime were successfully reproduced along the isoelectronic sequence of interest. All the observed transitions were interpreted with the help of multiconfigurational atomic structure calculations. In the case of magnesium, the photoabsorption data are compared with the ejected-electron spectra excited by low-energy electron impact of Pejcev et al. [J. Phys. B 10, 2389 (1977)]
IPMI test software for MicroTCA developments
To support our MicroTCA (AMC) module developments, and for diagnostic investigations in MicroTCA systems, we found a need to develop tools to exercise the IPMI functions of Management Controllers within the system. Based on the freely available ”ipmitool” program, we built a framework which allows to communicate with AMC Module Management Controllers through the Shelf Manager's network interface, without need to tap an IPMB. It contains functions to exercise various IPMI transactions and to check integrity and correctness of FRU (Field Replacable Unit) information and other data structures published by Management Controllers. The general structure of the library will be presented, as well as first results and future plans
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