Collaborative Proposal: Quest for an Electric Field-Induced Half-Metallic State in Metal Monochalcogenides

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Non-technical Description: Materials that are only a single or few atomic layers in thickness exhibit electronic properties that are profoundly altered with respect to those of bulk materials. These behaviors can be exploited for engineering new classes of optoelectronic devices with novel functionalities. The goal of this research project is to investigate a class of such extremely thin materials that are only one or few atomic layers thick, and seek to endow them with specific magnetic and electronic properties. The team envisions a material that, at the flip of a switch, can become electrically conducting or insulating, magnetic or non-magnetic. Such a material would be vital for the development of new technologies such as high-density memory storage devices and ultra-sensitive magnetic or optical sensors. These research efforts are integrated with plans to mentor and train the next generation of physicists and material scientists. In addition, both team members are active in recruiting and mentoring undergraduate and graduate students from under-represented groups, while also reaching out to high school teachers and students. The team collaborates with the National High Magnetic Field Laboratory at Florida State University to develop hands-on instructional materials for schools in surrounding North Florida counties.Technical Description: The ultimate goal of this research project is the achievement of gate-tunable ferromagnetism due to half-metallicity in monolayer and few-layer metal monochalcogenides, based on a recent theoretical proposal. These compounds, i.e. (In,Ga)(S, Se, Te), have been shown to exhibit high-room-temperature carrier mobility, thickness-dependent band gaps and high photoresponsivities. Although monochalcogenides are nonmagnetic, a recent first principles calculation predicts spin-split valence bands in their monolayers, with both the magnetic moment and the spin polarization energy depending strongly on density. Thus, a normal metal-ferromagnet-normal metal transition is expected as the hole density is tuned, with ferromagnetism and half-metallicity emerging when atomically thin monochalcogenides are hole-doped to ~10^13/cm^2. This research project strives to achieve this ambitious goal by overcoming a number of critical challenges, including synthesis of high quality material, device fabrication and optimization, and efficient gating techniques. Successful implementation of the research plan is expected to lead to new half-metallic systems that can be combined with other layered compounds in heterostructures to produce novel functionalities. In addition to training graduate students, both principal investigators continue their established efforts at mentoring undergraduate and high school students, while also recruiting and mentoring students from underrepresented groups.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.