Transverse spin correlations of the random transverse-field Ising model

The critical behavior of the random transverse-field Ising model in finite-dimensional lattices is governed by infinite disorder fixed points, several properties of which have already been calculated by the use of the strong disorder renormalization-group (SDRG) method. Here we extend these studies and calculate the connected transverse-spin correlation function by a numerical implementation of the SDRG method in d=1,2, and 3 dimensions. At the critical point an algebraic decay of the form ∼r-ηt is found, with a decay exponent being approximately ηt≈2+2d. In d=1 the results are related to dimer-dimer correlations in the random antiferromagnetic XX chain and have been tested by numerical calculations using free-fermionic techniques.