MAGNETIC-FIELD EFFECTS ON THE CORRELATION-FUNCTIONS IN THE ONE-DIMENSIONAL STRONGLY CORRELATED HUBBARD-MODEL

The momentum distribution function and spin-correlation functions are studied for the one-dimensional large-U Hubbard model with an emphasis on the effects of the magnetic field. A direct calculation of the correlation functions is carried out with the exact wave function, whose explicit form for the large-U limit was derived in a previous paper. Singularities are detected at K(F-sigma) and K(F-sigma) + 2K(F-sigma) in the momentum distribution function n-sigma(k), where K(F-sigma) is the Fermi wave number of the noninteracting electrons with a given magnetization. Similarly, the longitudinal spin-correlatio function S(zz)(k) has singularities at 2K(F-up) and K(F-down), while the transverse one S(xx)(K) is singular at K(F-up) + K(F-down) and K(F-up) - K(F-down). The nature of the singularities (i.e., critical exponents) is the singularities (i.e., critical exponents) is determined determined from an analysis of the size dependence. As a complementary approach, those critical exponents for the U/t --> infinity limit are explicitly calculated with conformal field theory. In this limit the exponents depends only on the magnetization and are independent of the electron density. The resulting exponents are consistent with the first results.