CHARGED AND SPIN-EXCITATION GAPS IN HALF-FILLED STRONGLY CORRELATED ELECTRON-SYSTEMS - A RIGOROUS RESULT

By exploiting the particle-hole symmetries of the Hubbard model, the p eriodic Anderson model, and the Kondo lattice model at half-filling an d by applying a generalized version of Lieb's spin-reflection positivi ty method, we show that the char,oed gaps of these models are always l arger than their spin-excitation gaps. This theorem confirms the previ ous results derived by either the variational approach or the density- matrix renormalization-group approach. [S0163-1829(98)07336-6].