QUANTUM ISING-MODEL IN A TRANSVERSE RANDOM-FIELD - A DENSITY-MATRIX RENORMALIZATION-GROUP ANALYSIS

The spin-1/2 quantum Ising chain in a transverse random magnetic field is studied by means of the density-matrix renormalization group. The system evolves from an ordered to a paramagnetic state as the amplitud e of the random field is increased. The dependence of the magnetizatio n on a uniform magnetic field in the z direction and the spontaneous m agnetization as a function of the amplitude of the transverse random m agnetic field are determined. The behavior of the spin-spin correlatio n function both above and at criticality is studied. The scaling laws for magnetization and correlation functions are tested against previou s numerical and renormalization-group results. [S0163-1829(97)05041-8] .