Radio Frequency and Terahertz Plasmons in Two Dimensional Electron Gases

Abstract

At the turn of the 21st century, the study of photonics, plasmonics and subwavelength phenomena became more and more intense as it became apparent that innovations in these fields could have important and widespread applications in miniaturizing electronic or photonic devices. Recent work in the Ham group have shown that the microwave to far infrared plasmons of 2D electron gases can achieve very small propagation velocities of <c/100, enabled by large kinetic inductances of the 2D electron gases, which promises size reduction factors of microwave circuits of 100 times or more. We will first build and describe simple circuit models of 2D electron gas plasmons, by computing equivalent capacitance, inductance, and resistances. Building a transmission line model from these circuit elements allows us to calculate plasmonic wave dispersions. Modifications to the dispersions are studied, and in particular, we examine how a periodic geometry can result in a plasmonic crystal. We propose and demonstrate these far infrared plasmonic crystals using the 2D electron gas in graphene, and we show that concepts from photonic and electronic crystals such as band engineering and symmetry selection rules apply. We also examine in great detail the origin and form of the kinetic inductance, which is key to the plasmonic response, and calculate the modifications to the Johnson-Nyquist noise that must necessarily result from any conductor with intrinsic inductance. An understanding of the high frequency noise spectrum is necessary to evaluate potential microwave and far infrared devices using these plasmons. Lastly, we show how non-reciprocal plasmons can arise non-magnetically, by simply applying a drift current to the electrons. The plasmons carried along by the electrons also drift with the same velocity as the drift velocity, which modifies the plasmon dispersion non-reciprocally, due to the drift motion being non-reciprocal. This principle may enable novel devices based on this principle in the future.