Since their development, semiconductors have operated on the principles of electronics, using positive and negative charges to flip millions or billions of tiny transistor switches to record and process information. The next iteration of computing, however, including low-power devices and quantum computers, will rely on new types of semiconductors that use a fundamental property of electrons called spin instead of electric charge. “Spintronics” will lead to faster, more efficient, and more powerful devices, enabling cutting-edge quantum computing, sensing and communications.
Yuan Ping. Photo by: Joel Hallberg.
Silicon has been the semiconductor of choice for electronics for more than half a century—however, finding materials best suited for spintronics is challenging, in particular non-magnetic semiconductors. But a study led by Yuan Ping, an associate professor of materials science and engineering at the University of Wisconsin-Madison, is providing direction in the hunt for the next great spintronic semiconductor.
Using a theoretical framework and new tools developed by Ping, she and her multi-university team of collaborators assessed the spintronic characteristics of a group of materials called halide perovskites, a promising class of semiconductors already used in LEDs, photovoltaic cells, lasers and other optoelectronic devices. The new paper in the journal Nature Communications shows that tweaking the symmetry and chemical composition of the easily altered halide perovskite crystals could lead to powerful new spintronic materials.
There are two key properties that make a good spintronic semiconductor. One is called spin orbit coupling, or the ease of manipulating the spin state. The other is called spin relaxation and decoherence time, or how long a spin state lasts. So far, no single spintronic material scores well when it comes to both of these properties. Gallium arsenide, for instance, has strong spin orbit coupling and a short spin lifespan, while diamond and graphene have long spin lifespans but weak spin orbit coupling.
Searching out materials that combine these two properties is often an educated guessing game. In previous work, Ping and her colleagues, who develop theory and tools to model and test quantum materials, created a first-principles predictive computational platform based on quantum mechanics for assessing these properties in various materials. The system enables rational design of new materials. Ping also hopes it will speed up the process of finding new materials for quantum information technologies.
In the new project, Ping applied this predictive platform, called the first-principles density-matrix dynamics method, to halide perovskites, which allowed the team to determine several unique characteristics of the materials. “If we understand the underlying mechanisms, then we can propose how to manipulate the symmetry, spin-orbit and electron-phonon coupling of the crystal to improve spintronic characteristics,” says Ping. “For example, in the paper, we propose a type of symmetry that increases the lifetime of the spin while also increasing the spin orbit coupling. This is a very unique phenomenon that people have not discussed before.”
Experimentalist colleagues on the team synthesized a high-quality halide perovskite film and measured the spin lifetime through time-resolved magneto-optics techniques, finding that the results lined up with the results of the theoretical modeling.
Ping says the work will allow researchers to continue to study and tune halide perovskites, which are good candidates for use in commercial spintronic devices since they are low cost, can perform at room temperature and do not require difficult synthesis techniques.
Other authors include Junqing Xu of Hefei University of Technology and the University of California, Santa Cruz; Kejun Li of the University of California, Santa Cruz; Uyen N. Huynh and Valy Vardeny of the University of Utah; Mayada Fadel and Ravishankar Sundararaman of Rensselaer Polytechnic Institute; and Jinson Huang of the University of North Carolina.
The authors acknowledge support for the theoretical development of spin dynamics in the presence of large spin-orbit coupling and magnetic field by the computational chemical science program within the Office of Science at DOE under grant No. DE-SC0023301. The experimental measurements of spin dynamics are supported as part of the Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the US Department of Energy (DOE).
Featured image credit: Xin Zhou