Materials in Reduced Dimensions and at the Nanoscale
In many of the materials that form the core of digital electronics and other technologies, reduced dimensionality plays a crucial role. The transistors that are the building blocks of computer chips flow current through two-dimensional electron gases created at the interface of two materials. While the operation of conventional transistors can be understood classically, the past 30 years have seen a revolution in low-dimensional quantum phenomena, both in semiconductors and new materials systems. The quantum Hall effect, first observed in silicon, is an example. In the presence of a strong magnetic field and at low temperatures, the dimensionless electric conductance is exactly equal to an integer. This integer encodes the winding of a quantum knot in the bulk electronic structure. Even more remarkable is the fractional quantum Hall effect, in which quantum knots can be tied and untied. These "braiding" operations manipulate quantum information, and might allow the realization of a quantum computer. Graphene, a single atomic layer of graphite first isolated in 2005, has provided a new material in which to study the quantum Hall effects and other phenomena. The recently-discovered topological insulators are materials that exhibit unbreakable edge or surface states as in the quantum Hall effect, but without a magnetic field. Rice researchers are at the forefront, pioneering new topological materials, developing the theories of edge and surface states, and creating devices to exploit their properties.
Materials at the nanoscale can also be structured to confine electrons in one dimension (quantum wires, including carbon nanotubes) and "zero" dimensions (quantum dots, or artificial atoms). Electrons under these constraints can exhibit fascinating phenomena, including collective motions that act as if electrons are split so that their spin and charge can move separately. Quantum dots and related systems, including molecular electronics devices, can act as tunable environments where electrons are manipulated at an individual level, and entangled with each other and other degrees of freedom. These can be model systems for examining the fundamental physics of electron-electron interactions, spin dynamics, electron-phonon couplings, and quantum entanglement, phenomena relevant to the frontiers of information technologies. Rice researchers have expertise and experience in the materials and techniques that enable these investigations.