Arno P. Kampf

Spin transport in Heisenberg antiferromagnets in two and three dimensions

We analyze spin transport in insulating antiferromagnets described by the XXZ Heisenberg model in two and three dimensions. Spin currents can be generated by a magnetic-field gradient or, in systems with spin-orbit coupling, perpendicular to a time-dependent electric field. The Kubo formula for the longitudinal spin conductivity is derived analogously to the Kubo formula for the optical conductivity of electronic systems. The spin conductivity is calculated within interacting spin-wave theory. In the Ising regime, the XXZ magnet is a spin insulator. For the isotropic Heisenberg model, the dimensionality of the system plays a crucial role: In d=3 the regular part of the spin conductivity vanishes linearly in the zero frequency limit, whereas in d=2 it approaches a finite zero frequency value.

Weak-coupling phase diagram of the extended Hubbard model with correlated-hopping interaction

A one-dimensional model of interacting electrons with on-site

η-pairing superconductivity in the Hubbard chain with pair hopping

U

Charge order in the pseudogap phase of cuprate superconductors

, nearest-neighbor

Magnetic flux periodicity of h / e in superconducting loops

V

Elementary excitations in dimerized and frustrated Heisenberg chains

, and correlated-hopping interaction

Exact many-electron ground states on the diamond Hubbard chain.

T^{\ast}

Route to Ferromagnetism in Organic Polymers

is studied at half-filling using the continuum-limit field theory approach. The ground state phase diagram is obtained for a wide range of coupling constants. In addition to the insulating spin- and charge-density wave phases for large

Crossover from h c / e to h c / 2 e current oscillations in rings of s -wave superconductors

U

Separation of Quasiparticle and Phononic Heat Currents in YBa 2 Cu 3 O 7 − δ

and