Topological materials are a newly discovered class of quantum materials that host topology-protected electronic states with great promise for next-generation technologies such as quantum computing, terahertz (THz) electronics and photonics, and infrared (IR) communications. One of the most intriguing aspects of topological materials is the tunability of their electronic band structure when films are just a few nanometers thin. In these thin films, the band topology and structure are highly dependent on the heterostructure parameters. This dependence not only creates novel electronic phases but also offers exceptional tunability for devices based on topological materials. In this talk, I will present my work on developing high-quality heterostructures of cadmium arsenide (Cd3As2), a prototype topological Dirac semimetal in bulk form, using molecular beam epitaxy (MBE). I will show that by changing the heterostructure parameters, the Cd3As2 thin film can adopt a variety of phases, including a highly desired two-dimensional (2D) topological insulator (TI) phase. I have proximitized these Cd3As2 thin films with superconductors to induce superconductivity in the topological electronic states. Topological superconductors are expected to host Majorana fermions, exotic quasiparticles that will be the bedrock of fault-tolerant quantum computing. The superconducting quantum interference patterns of Josephson junctions fabricated based on these hybrid 2D TI-superconductor structures show signatures of one-dimensional (1D) superconductivity while supercurrent flows in 2D form in films with trivial band structure. I will discuss the origin of the 1D superconductivity in the context of the 1D quantum spin Hall (QSH) edge states of the 2D TI phase. I will present further evidence of unconventional superconductivity by studying phase-sensitive devices fabricated based on these trivial and topological films. Finally, I will present my vision to expand this line of research at Rensselaer Polytechnic Institute (RPI) through creation of novel heterostructures, devices, and measurement approaches that support the generation and manipulation of Majorana fermions, with the ultimate goal of harnessing their non-abelian properties for applications in quantum computing. Building on my background in electronic and photonic devices based on wide bandgap semiconductors, my research plan will also develop heterostructures of topological materials for innovating devices that can address fundamental technological challenges in electronics and photonics. Some of the most unique device opportunities that make use of topological physics include THz cyclotron emission from massive Dirac fermions in 2D TIs, tunable mid-IR photodetectors based on topological Weyl semimetals, and THz transistors that benefit from the linear band dispersion and protected electronic states in topological semimetals and insulators. Through these efforts, I aim to develop a vigorously funded research program that extends our understanding of quantum materials and leads to radical device paradigms for future technologies.
Dr. Arman Rashidi is a postdoctoral scholar working with Prof. Susanne Stemmer in the Materials Department at the University of California, Santa Barbara (UCSB). His work involves developing novel nanoscale device platforms based on topological materials for quantum computing applications. Arman also mentors several Ph.D. students at UCSB and contributes to grant writing. Prior to joining UCSB in 2020, Arman earned his Ph.D. in Optical Science and Engineering in Prof. Daniel Feezell’s group at the University of New Mexico (UNM) in 2018. His research involved developing high-frequency InGaN emitters and understanding their fundamental quantum efficiency issues by studying their carrier dynamics using a new RF measurement technique that he developed at UNM. His work led to a dozen publications throughout his Ph.D., securing multiple grants across different agencies, and setting the basis for several future Ph.D. projects in Prof. Feezell’s group. From 2019-2020, Arman was granted funding by a light-emitting diode (LED) company to study carrier dynamics in micro-LEDs and served as the principal investigator of the project at UNM. Arman earned his bachelor's and master's degrees in Electrical Engineering from Shiraz University, Iran, in 2012 and 2014, respectively