Ground State Energy, Spin Gap and Hole Superconductivity on Square Lattice Heisenberg Antiferromagnet by Majorana Fermion

Abstract

By using Majorana fermion representations for spin 1/2 and hole operators on the square lattice antiferromagnet, the Neel ground state energy is calculated by a variational method. When a hole is doped on the lattice, the spin gap is formed as a condensate of the spin and the conduction hole, and becomes an elementary excitation. When more holes are doped and they exchange spin Majorana fermions between them, the spin gap becomes unstable. The instability of the spin gap leads to high Tc superconductivity, and a superconductive gap appears instead of the spin gap, where a superconductive hole is described by the Nambu representation of a massive Dirac fermion.