Condensed Matter Seminars

Classical and quantum spin systems have played an enormously important role in the study of magnetism. They provide excellent models to understand the ground state magnetic structure and low energy excitations of magnetic systems. In addition, they provide a rich arena for studying the physics of interacting many-body systems. In this talk I will discuss a very specific problem, namely the observation of an unusual ordering of spins, the so called uudd states, in quasi one-dimensional Heisenberg spin chains and anisotropic two-dimensional Heisenberg spin systems. Theoretical work to understand this and some related issues using both model spin Hamiltonians with competing interactions, exchange anisotropy, biquadratic exchange etc. and ab initio electronic structure calculations, will be discussed.