Magnetoresistance Effect of Black Phosphorus.

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1. An all-closed bismuth-flux method for preparing black P single crystals was improved from the point of view that chemical impurities will be reduced as much as possible and poisonous white P must be handled safely. In the method, the conversion of red P to white P and the growth of black P single crystals were performed in an evacuated quartz-glass apparatus without breaking the vacuum. Some crystal morphologies for needle-like crystals were observed and analyzed crystallographically.2. We have found that the needle crystals of black P show the lobT dependence of the conductivity and the logH dependence of the negative magnetoresistance ( vs H) below -10K. The negative magnetoresistance has a remarkable angular dependence of large for H and small got H//. These results show that two-dimensional Anderson localization is caused particularly in the black-P needle ceystals and the localization is suppressed by temperarure, magnetic field and electric field.It is also found that a Hall coefficient of black P is reversed from a hole-like plus sign to an electron-like minus sign. This suggests that a surface inversion-layer will be formed on the needle crystal.3. The energy band calculation of black P based on an ab-initio norm-conserving pseudopotential was presented. It has been that the results are in better agreement with experimental results regarding the energy band, density of states, reflectance spectra, static dielectric constant, plasma frequency, except for effective masses. The energy band calculation under pressure was also performed. It has been found that the results are in good agreement with the experimental results of structural properties and pressure dependencies of energy gap and TAy phonon frequency.Theoretical and experimental results of black P such as a narrow and direct-allowed-transition band-gap and a layered structure suggest that black P has a potential use to an infrared detector and new intercalation compounds.