MAGNETISM IN MULTIBAND ITINERANT ELECTRON SYSTEMS
    By now it is well established that the ground state of the two-dimensional, single band Hubbard model and its strong coupling limit, the spin-1/2 Heisenberg model, have long range antiferromagnetic order. Some of the strongest evidence for this conclusion is based on numerical work, significantly Quantum Monte Carlo Simulations. We have extended these studies to the antiferromagnetic-paramagnetic phase transition driven by interband hybridization in multiband Hubbard models. In coupled two-dimensional Hubbard layers we find that interplane hybridization decreases local moments and, eventually, drives singlet formation between the sheets and the destruction of long range magnetic order.

    Similarly, in the two-dimensional periodic Anderson model, spin liquid behavior supplants magnetic order as the hopping t(pd) between localized and conduction bands is increased.[3] One can characterize this behavior either through the spin-spin correlations directly, or, alternately, through calculation of the charge and spin gaps. One finds that a charge gap is present at all t(pd), but that a spin gap begins to develop only past a critical value of t(pd). We have computed this critical value as a function of the on site repulsion U on the f electron sites, allowing us to map out the magnetic phase diagram of the periodic Anderson model at half-filling.

    Magnetic moment formation and Kondo screening is also important in the Cerium Volume collapse transition.

    Finally, magnetic fields can be used to tune across the metal-insulator phase transition.

    Relevant Publications:

    [51.] "Magnetic and Pairing Correlations in Coupled Hubbard Planes," R.T. Scalettar, J.W. Cannon, D.J. Scalapino, and R.L. Sugar, Phys. Rev. B50, 13419 (1994).

    [53.] "Competition Between Antiferromagnetic Order and Spin Liquid Behavior in the Two-Dimensional Periodic Anderson Model at Half-Filling," M. Vekic, J.W. Cannon, D.J. Scalapino, R.T. Scalettar, and R.L. Sugar, Phys. Rev. Lett. 74, 2367 (1995).

    [55.] "Magnetism and Spin Liquid Behavior in a Two Layer Hubbard Model," R.T. Scalettar, J. of Low Temp. Phys. 99, 499 (1995).

    [58.] "Insulating States of Correlated Electrons," D.J. Scalapino, R.L. Sugar, R. Noack, S.R. White, R.T. Scalettar, M. Vekic, and J.W. Cannon, J. of Low Temp. Phys. 99, 487 (1995). \+&&\cr

    [66.] "One particle spectral weight of the three dimensional single band Hubbard model." M. Ulmke, R.T. Scalettar, A. Nazarenko, and E. Dagotto, Phys. Rev. B54, 16523 (1996).

    [71.] "Ferromagnetism in an Orbitally Degenerate Hubbard Model", J. Kuei and R.T. Scalettar, Phys. Rev. B55, 14968 (1997).

    [87.] "Magnetic and Thermodynamic Properties of the Three-Dimensional Periodic Anderson Hamiltonian", Carey Huscroft, A.K. McMahan, and R.T. Scalettar, Phys. Rev. Lett. 82, 2342 (1999).

    [91.] "Similarities between the Hubbard and Periodic Anderson Models at Finite Temperatures", K. Held, C. Huscroft, R.T. Scalettar, and A.K. McMahan, Phys. Rev. Lett. 85, 373 (2000).

    [112.] "The Cerium Volume Collapse: Results from the merger of dynamical mean-field theory and local density approximation,'' K. Held, A.K. McMahan, and R.T. Scalettar, Phys. Rev. Lett. 87, 276404 (2001).

    [120.] "Thermodynamic and spectral properties of compressed Ce calculated by the merger of the local density approximation and dynamical mean field theory," A. K. McMahan, K. Held, and R. T. Scalettar, Phys. Rev. B67, 075108 (2003).

    [125.] "Interacting electrons in a two-dimensional disordered environment: Effect of a Zeeman magnetic field,'' P.J.H. Denteneer and R.T. Scalettar, Phys. Rev. Lett. 90, 246401 (2003).