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表现出的电子性质与大块材料相比发生了深刻的变化。这些行为可以用于工程设计具有新功能的新型光电器件。该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。该团队设想了一种材料，在开关的翻转下，可以成为导电或绝缘，磁性或非磁性。这种材料对于高密度存储设备和超灵敏磁或光传感器等新技术的开发至关重要。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，两个团队成员都积极招募和指导来自代表性不足群体的本科生和研究生，同时也接触高中教师和学生。该团队与佛罗里达州立大学的国家高磁场实验室合作，为周围北佛罗里达县的学校开发实践教学材料。技术描述：本研究项目的最终目标是根据最近的理论建议，在单层和少层金属单硫族化物中实现半金属性的门可调铁磁性。这些化合物，即（In，Ga）（S，Se，Te），已被证明具有高的室温载流子迁移率，厚度依赖的带隙和高的光响应性。虽然单硫族化物是双金属，但最近的第一原理计算预测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，随着空穴密度的调整，可以预期正常金属-铁磁体-正常金属的转变，当原子级薄的单硫族化物空穴掺杂到约10^13/cm ^2时，出现铁磁性和半金属性。该研究项目致力于通过克服许多关键挑战来实现这一雄心勃勃的目标，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。该研究计划的成功实施有望产生新的半金属体系，这些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。除了培养研究生外，两位主要研究者还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NSF的法定使命，并通过使用基金会的智力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.