Dark Vertical Transport of Electrons in Polaritonic Semiconductor Heterostructures

Abstract

Building on our previous experience with resonant tunneling diodes strongly coupled to the cavity field [1], we present a set of semiconductor heterostructures optimised to study the dark vertical transport of electrons induced by virtual photons. Recently, many advances have led to a better understanding of the influence of Casimir photons on quantum systems, including a significant enhancement of conductivity in organic semiconductors [2], the breakdown of topological protection caused by cavity vacuum fields [3], and the self-assembly of microcavities due to a balance between Casimir and Van-der-Waals forces [4]. Recent theories attempt to explain these effects, emphasising the importance of the antiresonant terms in the light matter coupling Hamiltonian [5,6]. We investigate the coupling of electrons to virtual photons using different designs of semiconductor quantum structures. The first approach utilizes a triple-barrier resonant tunneling diode, as shown in Fig. 1. The structure is embedded in metal-metal patch resonator arrays which serve both as cavities and electrical contacts. In this system the cavity leads to an enhanced confinement of the electromagnetic mode, allowing the strong coupling regime to be reached. Our research involves a measurement of the transport characteristics at different temperatures, as depicted in Fig. 2. Moreover, in order to verify the strong coupling behaviour IR-spectroscopy measurements were performed (Fig. 3) which clearly show the polariton-splitting due to the interaction with the intersubband transition of the resonant tunneling diode. The second approach, depicted in Fig. 4, includes the design of a QWIP-like multi quantum well structure. Research performed on QWIPs operating in the strong coupling regime not only led to an enhancement of their performance capabilities but also enabled a better understanding of the fundamental behaviour of polaritonic devices [7]. As the basic building blocks of a QWIP are well-understood, it can be used as a tool to gain a deep insight into the coupling of electrons and virtual photons, which is a key objective of our work.