BQ3: How does quantum physics explain and predict novel materials?

The properties of systems with many constituents sometimes bear little resemblance to the properties of the components. This has been known empirically for millennia: bronze (copper with added tin or arsenic) is much harder than its components, and its manufacture ushered in the dawn of urban civilization. More complex systems, which are commonly called quantum materials, are even more interesting and provide fertile ground for novel quantum physics, the critical underpinning of much of modern materials science and device design.

Crystals that combine several elements show new phases and have dramatic electronic or magnetic properties. One famous example is high-temperature superconductivity, where proof-of-principle demonstrations stunned the physics world thirty years ago, but commercial applications are just emerging. Engineered quantum materials, made with metallic nanostructures or superconducting elements, can have exotic properties not found in nature, such as very strong coupling between light and matter. The presence of the matter makes photons, normally non-interacting, interact with each other. On the other hand, the emission from the matter can be increased enormously, especially by using nanostructured matter.

Quantum theory guides the design of novel materials and provides the fundamental understanding of many chemical and biological processes. In nanoscale quantum physics, new phenomena occur as the size of the system is intermediate between microscopic and macroscopic—moving an electron, for instance, requires paying a charging energy. Both electronic and photonic properties change as a result. The exquisite control now possible in nanosystems leads to sensitive probes of the new physics. New regimes will continue to gain in importance; for example, we are not far from the point where computers will have to count electrons (see Big Question 6).

Modern fabrication techniques, mostly driven by solid state physics, let us create completely new kinds of quantum materials with remarkable properties such as metamaterials. These are best known to the public for their ability in principle to mimic invisibility cloaks, but there are many more practical applications in the short term, such as the ability to create lenses which bypass the traditional diffraction limit of light (and this could be incredibly important for the future of lithography).

Research in this field tends to be small-scale (tabletop) experimental work, and theory which is very closely coupled to experiment. Duke primary and secondary faculty have substantial accomplishments in creating next-generation metamaterials, single-photon optical sources, a variety of advanced devices (such as graphene-based Josephson junctions) and technologies for controlling light (such as femtosecond laser pulse shaping). They fabricate new materials with interesting quantum spin properties, such as superconductivity and frustrated magnetism, as well as ultranarrow superconducting nanowires, thermoelectrics, spin-caloritronics, and photovoltaics. They explore theoretical properties of noise-based dynamical systems, quantum wires and dots. This work strongly connects with the Departments of Materials Science and Mechanical Engineering (MEMS) and Electrical and Computer Engineering (ECE) at the Pratt School of Engineering.

Research at Duke University