Magnetic and electronic excitations in low-dimensional and nanostructured materials

点击翻译按钮获取中文摘要

Research on magnetic materials with one or more lengths in the submicron range, as in low-dimensional nanostructures and arrays, is driven by their immense technological potential (for high-frequency devices, magnetic memories, fast switches, etc). For theory there is a need to understand at a fundamental level the dynamical processes on these length scales. This provides the primary motivation for this proposed theoretical research on the collective magnetic excitations (or waves) together with the electronic excitations. Taking into account the challenging effects due to surfaces and interfaces is important, since nanostructured magnetic materials may display novel characteristics that are absent in their bulk constituent materials.***I will study the linear and nonlinear dynamics of magnetic spin waves in arrays of magnetic nano-elements and the related electronic and magnetic effects in carbon-based nanomaterials like graphene. For example, the expanding field of magnonics concerns artificial media like patterned thin films with a repeating (or periodic) variation in their magnetic properties. The frequencies and directions of the spin waves can be controlled using this periodicity and an applied magnetic field, as the basis for device applications. In spintronics there are also moving electronic charges, giving electric currents in the materials; these influence the spin waves allowing further device applications. In the nonlinear dynamics the effects of interactions between the spin waves come into play, and I will study these on the small length scales. Some nonlinear effects that I will focus on include spin-wave decay and instability, particularly in a strong microwave field, and the magnetic Bose-Einstein condensation. The choices of magnetic elements in their periodic or quasiperiodic arrays provide a variety of situations for exploiting new properties for magnetic device applications. ***Methods include many-body and quantum-field theories (diagrammatic methods, Green's functions, response theory). From previous work I have expertise in specialized methods for spin systems, which I will adapt for nanomaterials in nonlinear regimes with a microwave pumping field being applied. I will utilize collaborations with experimentalists using inelastic light scattering, ferromagnetic and electron-spin resonance, and microwave spectroscopy. My research will be significant for insights to dynamical processes at very small length scales and may lead to new developments for high-frequency devices. Understanding the quantum statistics in these systems when they are far from equilibrium (due to the microwave fields) or at higher temperatures (when nonlinear processes are enhanced) will be important aspects of this work. A better knowledge of the magnetic effects in graphene nanostructures is an important goal for new applications in low-dimensional materials.