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

非技术描述：只有一个或几个原子层厚度的材料，其电子特性与块状材料相比发生了深刻的变化。这些行为可以用于设计具有新功能的新型光电器件。这个研究项目的目标是研究一类只有一个或几个原子层厚的极薄材料，并寻求赋予它们特定的磁性和电子特性。该团队设想一种材料，在开关的翻转下，可以变成导电或绝缘，磁性或非磁性。这种材料对于新技术的发展至关重要，如高密度存储设备和超灵敏的磁或光学传感器。这些研究工作与指导和培训下一代物理学家和材料科学家的计划相结合。此外，这两个团队成员都积极从代表性不足的群体中招募和指导本科生和研究生，同时也与高中教师和学生接触。该团队与佛罗里达州立大学的国家高磁场实验室合作，为北佛罗里达周边县的学校开发动手教学材料。技术描述：本研究项目的最终目标是在最近的理论建议的基础上，由于单层和几层金属单硫族化合物的半金属性，实现栅极可调谐铁磁性。这些化合物，即（In,Ga）（S, Se, Te），已被证明具有高室温载流子迁移率，厚度相关的带隙和高光响应性。虽然单硫族化合物是非磁性的，但最近的第一性原理计算预测了其单层中的自旋分裂价带，磁矩和自旋极化能都强烈依赖于密度。因此，当空穴密度被调谐时，一个正常的金属-铁磁性-正常金属转变有望实现，当原子薄的单硫族化合物空穴掺杂到~10^13/cm^2时，铁磁性和半金属性就会出现。该研究项目通过克服一系列关键挑战，包括高质量材料的合成、器件制造和优化以及高效的门控技术，努力实现这一雄心勃勃的目标。该研究计划的成功实施有望导致新的半金属体系，可以与异质结构中的其他层状化合物结合，产生新的功能。除了培训研究生之外，两位主要研究人员继续他们在指导本科生和高中生方面的既定努力，同时也从代表性不足的群体中招募和指导学生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.