Switchable Persistent Spin Helix Devices

功率消耗和能源消耗是当前基于硅场效应晶体管的计算技术未来可扩展性的关键限制因素。由于具有低开关能量的潜力，自旋电子器件利用电子的自旋而不是电荷来携带信息，长期以来一直被用作数字计算和模拟设备的替代方法。然而，实现自旋电子器件的潜力需要克服一些基本挑战。首先，在传统的自旋电子材料如砷化镓中，弱的自旋-轨道耦合需要电子在大型设备上的传输，以允许控制自旋。相比之下，使用具有高自旋-轨道耦合的材料来制造更小的器件会导致自旋信息的快速丢失，这是由于去相化：自旋迅速旋转并彼此变得不同。PI建议通过利用具有一种特殊类型的自旋行为的材料来解决这两个挑战，这种特殊类型的自旋行为称为持久自旋螺旋，其中电子自旋即使在快速旋转时也保持同步，使自旋信息即使在高自旋轨道材料中也能够保持更长时间。具体地说，通过在具有强自旋轨道耦合的van der Waals固体中使用电场可调的持久自旋螺旋，PI提出了一种新型的自旋电子器件材料，这种材料的自旋行为可以通过电场敏感地控制，并且由于显著增强的自旋轨道耦合，设备的尺寸可以减少两到三个数量级。这将有助于创新用于高性能和低功耗计算的竞争性自旋场效应晶体管的设计。该奖项还旨在促进在快速增长的自旋电子材料和器件领域对历史上未被充分代表的群体的研究培训，从而为未来微电子学的发展贡献技术诀窍和劳动力。PI建议了解电场调谐对称性和哈密顿量对自旋电子器件中具有强烈自旋轨道耦合的方形范德瓦尔斯晶体的自旋织构、自旋动力学和自旋输运的影响。由于所选材料的基面和自然量子阱结构的正方形对称性，当外加电场沿所需的晶体取向施加时，预期会产生持久的自旋螺旋型自旋轨道场。利用持久的自旋螺旋态和强的自旋-轨道耦合，PI有望实现电场/电压可切换的对称性保护的长程相干自旋输运。模型材料包括空气稳定、光刻友好的范德华晶体Bi2O2Se和BiOI，模型器件包括基于持久自旋螺旋的自旋场效应晶体管。提议的启用和调整持久自旋螺旋的方法不需要在III-V中常见的Rashba和Dresselhaus场之间仔细平衡。这使得所提出的模型系统成为探索自旋场效应晶体管的可靠平台。PI将生长单晶取向控制的自旋电子四方范德华半导体，并制造持久的自旋螺旋基场效应晶体管。PI将通过计算预测和实验揭示模型材料和器件中的自旋极化能带结构，以及持续自旋螺旋的动力学和波长。PIS还将展示基于持久自旋螺旋的场效应晶体管的概念验证，并揭示器件结构/尺寸、栅电介质、外部电压/极化和温度对自旋场效应晶体管的特性和性能的影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Power dissipation and energy consumption are a key limiting factor in the future scalability of present computing technologies based on silicon field-effect transistors. Due to their potential for a low switching energy, spintronic devices that leverage the spin of electrons to carry information instead of their charge have long been pursued as an alternative approach, both for digital computing and analog devices. However, realizing the potential of spintronic devices requires overcoming a few basic challenges. First, weak spin-orbit coupling in conventional spintronic materials such as GaAs necessitates transport of electrons over large devices to allow control of the spin. In contrast, using a material with high spin-orbit coupling to make smaller devices leads to rapid loss of spin information due to dephasing: spins rapidly rotating and becoming out of phase with each other. The PIs propose to address these two challenges by leveraging materials with a special class of spin behavior called the persistent spin helix, where electron spins remain in phase even when rotating rapidly, enabling spin information to be retained longer even in high spin-orbit materials. Specifically, by using electric-field tunable persistent spin helix in van der Waals solids with strong spin-orbit coupling, the PIs propose to enable a new class of materials for spintronic devices, where the spin behavior can be sensitively controlled by electric fields and where the device dimensions can be reduced by two to three orders of magnitude due to the significantly stronger spin-orbit coupling. This would help innovate the design of competitive spin field-effect transistors for high-performance and low-power computing. This award also aims to promote research training to historically underrepresented groups in the rapidly growing field of spintronic materials and devices, and thereby contribute to both the technical knowhow and workforce for the development of future microelectronics.The PIs propose to understand the effect of electric field-tuned symmetry and Hamiltonian on the spin texture, spin dynamics, and spin transport of square van der Waals crystals with strong spin-orbit coupling for spintronic devices. With the square symmetry of the basal plane and natural quantum well structures of selected materials, when an external electric field is applied along desired crystallographic orientations, persistent spin helix-type spin-orbit field is expected. With persistent spin helix states and strong spin-orbit coupling, the PIs expect to achieve electric field/electric voltage-switchable symmetry-protected long-range coherent spin transport. The model materials include air-stable, lithography-friendly van der Waals crystals Bi2O2Se and BiOI, and the model devices include persistent spin helix-based spin field effect transistors. The proposed approach for enabling and tuning persistent spin helix does not require careful balance between Rashba and Dresselhaus fields commonly seen in III-V. This makes the proposed model systems a robust platform for exploring spin field effect transistor. The PIs will grow single crystalline orientation-controlled spintronic tetragonal van der Waals semiconductors and fabricate persistent spin helix-based field effect transistors. The PIs will computationally predict and experimentally reveal the spin-polarized band structure, and dynamics and wavelength of persistent spin helix in the model materials and devices. The PIs will also demonstrate the proof-of-concept persistent spin helix-based field effect transistors and reveal the effects of device structure/dimension, gate dielectrics, external voltage/polarization, and temperature on the characteristics and performance of the spin field effect transistor.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.