Density matrix renormalization group study of the S=1/2 antiferromagnetic Heisenberg chains with quasiperiodic exchange modulation

The S = 1/2 antiferromagnetic XXZ chains with precious mean quasiperiodic e xchange modulation is studied by the density matrix renormalization group m ethod. It is found that the energy gap Delta E scales as exp(-cN(omega)) wi th the system size N if the Ising component of the exchange coupling is ant iferromagnetic. This is in contrast to the XY case in which Delta E similar to N-z. Our results are not only consistent with the bosonization analysis of Vidal, Mouhanna and Giamarchi(9)) but also clarify the nature of the st rong coupling ground state which is unreachable within the weak coupling ca lculation of Ref. 9).