Coulomb coupling of like charges due to negative reduced effective mass

The shape of Fermi contour high-temperature superconductors (HTS) has the i mportant feature. Namely, the components of hole pair reduced effective mas s are of opposite sign at the most part of the Fermi contour. As a result, it is possible a rise of a hole pairing dire to direct Coulomb interaction. This conception is used to explain the essential distinction between the t emperature of a pseudogap arising and the temperature of the superconductor transition in the case of underdoped HTS compounds.