The search and manipulation of innovative properties developing from the quantum nature of matter could lead to next-generation quantum computers and electronics. However, finding or designing materials capable of hosting such quantum interactions is indeed a problematic task.
Harmonizing multiple quantum mechanical properties, which often do not coexist together, and trying to do it by design is a highly complex challenge.
James Rondinelli, Northwestern Engineering
But Rondinelli and a global team of computational and theoretical researchers have done just that. Besides demonstrating that multiple quantum interactions can coexist in one material, the team also succeeded in discovering how an electric field can be employed for controlling these interactions to tune the material’s properties.
This innovation could allow low-power, ultrafast electronics and quantum computers that work extremely faster than existing models in the areas of data acquisition, exchange, and processing.
The research published online on Feb 5th, 2018, in the journal Nature Communications has been supported by the US Army Research Office, National Science Foundation of China, German Research Foundation, and China’s National Science Fund for Distinguished Young Scholars. James Rondinelli, the Morris E. Fine Junior Professor in Materials and Manufacturing in Northwestern’s McCormick School of Engineering, and Cesare Franchini, professor of quantum materials modeling at the University of Vienna, are the co-corresponding authors of the paper. Jiangang He, a postdoctoral fellow at Northwestern, and Franchini are the paper’s co-first authors.
Quantum mechanical interactions administer the potential of and speed with which electrons can pass through a material. This establishes whether a material is an insulator or conductor. It also controls whether or not the material displays ferroelectricity, or presents an electrical polarization.
The possibility of accessing multiple order phases, which rely on different quantum-mechanical interactions in the same material, is a challenging fundamental issue and imperative for delivering on the promises that quantum information sciences can offer.
Cesare Franchini, Professor of Quantum Materials Modeling, The University of Vienna
Using computational simulations carried out at the Vienna Scientific Cluster, the team succeeded in discovering coexisting quantum-mechanical interactions in the compound silver-bismuth-oxide. Bismuth, a post-transition metal, allows the spin of the electron to work together with its own motion — a characteristic that has no equivalence in classical physics. It also does not display inversion symmetry, indicating that ferroelectricity should be present when the material is an electrical insulator. Researches applied an electric field to the material in order to control whether the electron spins were coupled in pairs (displaying Weyl-fermions) or separated (showing Rashba-splitting) as well as whether the system is electrically conductive or not.
This is the first real case of a topological quantum transition from a ferroelectric insulator to a non-ferroelectric semi-metal. This is like awakening a different kind of quantum interactions that are quietly sleeping in the same house without knowing each other.