Mind the Gap: Quantum Effects and Optical Magnetism in Plasmonic Particle Junctions
Electrons and photons can coexist as a single entity called a surface plasmon—an elementary excitation found at the interface between a conductor and an insulator. Plasmons are evident in the vivid hues of rose windows, which derive their color from small metallic nanoparticles embedded in the glass. They also provide the basis for color-changing biosensors, photo-thermal cancer treatments, improved photovoltaic cell efficiencies, and nano-optical tweezers. While most applications have relied on classical plasmonic effects, quantum phenomena can also strongly influence the plasmonic properties of nanometer-scale systems.
In this presentation, I’ll describe my group’s efforts to probe plasmon modes spanning both classical and quantum domains. We first explore the plasmon resonances of individual nanoparticles as they transition from a classical to a quantum-influenced regime. Then, using real-time manipulation of plasmonic particles, we investigate plasmonic coupling between pairs of particles separated by nanometer- and Angstrom-scale gaps. For sufficiently small separations, we observe the effects of quantum tunneling between particles on the plasmonic resonances.
Finally, using the properties of coupled metallic nanoparticles, we demonstrate the colloidal synthesis of an isotropic metafluid or "metamaterial paint" that exhibits a strong magnetic response at visible frequencies. By combining the electric and magnetic resonances of non-magnetic nanoparticles, this metamaterial can achieve negative permeabilities and refractive indices. The ability to assemble, probe, and control both classical and quantum plasmonic junctions with electric and magnetic resonances may enable new opportunities in fields ranging from catalysis to molecularopto-electronics.