Tailoring spin and magnetism in systems of reduced dimensionality

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A departure from conventional, bulk-like materials offers intriguing possibilities to study and predict unusual fundamental phenomena as well as to realize novel applications. Two striking examples of what could be feasible in systems of reduced dimensionality have recently been demonstrated by the research on spintronics and graphene, also recognized by the 2007 and 2010 Nobel Prizes in Physics, respectively.Graphene has already attracted immense interest due to its excellent transport and optical properties, which make it an attractive candidate for possible applications in nanoscale electronics and optoelectronics. On the other hand, advances in spintronics have, over the past decade, enabled a 1,000-fold increase in the capacity of computer hard drives in metal-based structures that utilize magneto-resistive effects. However, this represents only the tip of the iceberg. The control of spin and magnetism in a wide class of materials and their nanostructures has the potential for a much broader impact. In fact, experimental breakthroughs in graphene suggest that it is particularly suitable for spintronics. For specific applications, graphene spintronics could significantly outperform the existing conventional counterparts.The research proposed here therefore seeks to theoretically elucidate novel phenomena in selected systems of reduced dimensionality, such as graphene, quantum wells (QWs), and quantum dots (QDs):In the first project, we will examine the magneto-optical properties of graphene-based systems. Our preliminary work suggests that the optical and magneto-optical response of monolayer graphene can be drastically modified by the substrate. Therefore we will systematically study the role of different substrates on magneto-optical and spin-optical conductivities in graphene-based structures, such as bilayer graphene, nanoribbons, and nanodiscs, as well as develop a related theory for the Kerr effect.In a closely related project, we will also study the coupling between plasmons and phonons in such structures and its effect on their optical properties.Building on our previous work on HgTe/CdTe QWs, we will study the effects of edge and surface states on the (magneto-)optical conductivity in topological insulators. We will look for signatures of the crossover between the inverted and normal band structures at a finite magnetic field.Finally, we will develop a microscopic model for the formation of magnetic polarons in QDs and provide theoretical input for several ongoing experiments conducted at the University at Buffalo, including the prospect for a peculiar thermally-enhanced magnetism. In analogy to the project on HgTe/CdTe QWs, we will also explore the possibility of band inversion in QDs and its optical signatures that could reveal related unconventional spin and magnetic ordering.