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 exchange modulation is studied by the density matrix renormalization group method. It is found that the energy gap Delta E scales as exp(-cN(omega)) with the system size N if the Ising component of the exchange coupling is antiferromagnetic. 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 strong coupling ground state which is unreachable within the weak coupling calculation of Ref. 9).