122608189
Study of GaAs as a material for solar neutrino detectors
Abstract Semi-insulating GaAs crystals grown by liquid encapsulated Czochralski technique from Ga-rich melts were evaluated as a possible material for radiation detectors with a high active layer thickness. The density of deep traps, particularly the midgap EL2 donors pinning the Fermi level, was measured by various techniques in conducting and semi-insulating samples. For EL2 traps, a direct evidence of their partial neutralization in the space charge region of reverse biased Schottky diodes due to nonequilibrium capture of electrons is presented for the first time. It is shown that the density of EL2 centers decreases with decreased As composition of the melt very gradually, especially for post-growth annealed samples. Subsequently, if one aims to decrease the EL2 density to such an extent that it would make a serious impact on the depletion layer width in GaAs-based detectors one has to grow semi-insulating GaAs crystals from melts with As composition below about 43% which poses a problem for the preservation of high resistivity of the material due to the relatively high concentration of compensating acceptors.
121164015
Bulk GaAs as a solar neutrino detector
A GaAs detector may offer the unique possibility to independently study neutrino properties and solar physics. The ability to measure the flux of p–p, 7Be and pep solar neutrinos would allow one to approach a solution of the “solar neutrino problem”, i.e. the explanation of the significant deficit in observed capture rate of solar neutrinos. A large GaAs solar neutrino detector would allow to measure parameters for possible Mikheyev–Smirnov–Wolfenstein neutrino oscillations with unprecedented precision. A model-independent test for sterile neutrinos is also possible. A direct measurement of the temperature profile of the Sun center appears feasible. A GaAs detector would also provide the ability to observe neutral current interactions in addition to addressing a wide range of other interesting physics. 
 
In order to measure the p–p, pep and 7Be neutrinos a detector is required with low threshold (< 350 keV), good energy resolution (< 2 keV) and low background. A GaAs solid-state detector could meet the listed requirements. A large GaAs detector would be composed of approximately 40,000 intrinsic GaAs crystals, each weighting 3.2 kg. Such a detector would have a mass of 125 ton and would contain 60 ton of Ga occupying a volume of roughly 3 m on one side. Previous efforts by many groups have resulted in producing very small detectors with reasonably good resolution. However, it has thus far proved impossible to make large detectors with good resolution. Thus, a solar neutrino detector such as the one described above is obviously very ambitious, but the scientific motivation is sufficiently high that we have begun a research and development program with the goal of determining the technical feasibility of constructing large GaAs crystals with the requisite electronic properties to serve as particle detectors.
118103020
Metastable States of Two-Dimensional Isotropic Ferromagnets
123585824
Quantum Gravity in Two-Dimensions
Two dimensional induced quantum gravity is analyzed. By the use of light-cone gauge we derive a gravitational analogue of the Wess-Zumino action and discover its amazing connection with SL (2, ℝ) current algebra. The latter permits us to find differential equations for the correlation functions.