MOMENTUM DISTRIBUTION IN KAPPA-(BEDT-TTF)2CU[N(CN)2]BR ORGANIC SUPERCONDUCTOR MEASURED BY POSITRON-ANNIHILATION - SEARCH FOR THE FERMI-SURFACE

We report the first precise measurement of the positron-electron momentum distribution in an organic superconducting single crystal kappa-(BEDT-TTF)2Cu[N(CN)2] Br by the 2D-ACAR method. The anisotropy in the raw spectrum has the appropriate symmetry and is consistent with the structure factors of the space group of the crystal. The LCW-folded k-space density is discussed and compared with the Fermi surface prediction of a HMO calculation. Substantial discrepancies between the experimental results and the existing theory are found.