Development of Chiral Charge Density Wave Devices

本提案的目标是扩展我们对手性电荷密度波材料性质的基本理解，并利用其性质在新的光电器件中。手性电荷域的操作将对凝聚态物理产生革命性的影响，它将为基于集体电子激发的器件打开大门。电子领域使用集体电荷系统的主要优点是功耗低、信息存储密度高、速度快。基础研究将包括宏观电子和光学性质表征以及精心设计的二维材料和器件的手性电荷密度波性质的原子尺度研究。该项目将为学生和青年研究人员在材料科学、凝聚态物理和光电子器件工程等领域开展现代基础研究提供必要的工具。由于设计的研究活动是高度跨学科的，学生将被激发跨学科的课程，如纳米科学，电子和扫描探针显微镜和纳米制造。该计划是通过(a)在本科和研究生阶段结合现有的纳米科学、纳米电子学和固态物理课程的研究元素来扩大学生的参与和欣赏；(b)训练学生使用最先进的制造和表征工具，(c)让学生接触到不同组织的研究企业和合作研究。这项工作将培养一名博士生和几名本科生。通过高级论文工作经验和科学研究俱乐部以及学院的开放日向当地高中伸出援助之手，这是为高中生攻读科学和工程学位做准备的过度战略的一部分。手性打破了空间反演对称性，导致了意想不到的新电子性质，特别是在降维系统中。在许多情况下，无论是在原子尺度上还是在介观尺度上，电子手性都是由系统的特定结构促进的。最近，人们发现电荷密度波这一被广泛研究的宏观相关电子态也具有手性。该方案探索了利用纳米级的反手性结构域作为存储和逻辑单元的基本元素的机会，这些结构域与畴壁分开。在这一建议中，我们将扩展对飞秒光扰动和纳秒电流脉冲的手性CDW耦合的动力学性质的基本理解。系统在回到平衡状态之前所经历的激发亚稳态的动力学可能包括非常规的秩序，如铁电性、CDW或超导性。这些现象的起源是由于存在各种类型的对称破缺（TiSe2中的反演对称），从而产生简并基态。在低功率电子器件中利用这些亚稳态是有机会的。我们还将优化TiSe2薄膜的生长，以实现高效的器件制造。探讨了应变和掺杂对手性CDW热力学的影响。

The goal of this proposal is to extend our fundamental understanding of the properties of chiral charge density wave materials and utilize its properties in new opto-electronic devices. Manipulation of chiral charge domains will be transformative to the condensed matter physics and it will open the doors to devices based on collective electron excitations. The main advantage of using collective charge systems for electronics is lower power dissipation, high density of information storage and high speed. The fundamental studies will involve both macroscopic electronic and optical properties characterization and atomic scale investigations of the chiral charge density wave properties in carefully engineered two-dimensional materials and devices.The program will provide students and young researchers with necessary tools to carry out modern fundamental research in the fields of materials science, condensed matter physics and optoelectronic device engineering. Since the designed research activities are highly interdisciplinary, the students will be stimulated to take classes across disciplines, such as nanoscience, electron and scanning probe microscopy and nanofabrication. The plan is to broaden participation and appreciation of students through (a) incorporating elements of the research in existing nanoscience, nano-electronics and solid-state physics courses at both the undergraduate and graduate level; (b) train students to use state of the art fabrication and characterization tools and (c) expose the students to research enterprise and collaborative research across different organizations.This work should lead to training a PhD student and several undergraduate students. Outreach to local area high schools through senior thesis work experience and science research clubs as well as College' s open houses are part of the overreaching strategy to prepare high school students to pursue science and engineering degrees.Chirality breaks down the spatial inversion symmetry and results in unexpected new electronic properties, in particular in systems with reduced dimensionality. In many cases the electronic chirality is facilitated by the specific structure of the system in which it emerges, either on atomic scale or on mesoscopic scale. Recently, it was discovered that one of the well-studied macroscopically correlated electronic state, the charge density wave, also exhibits chiral properties. This proposal explores the opportunity to use the nanometer-size domains of opposite chirality that are separated with domain walls as basic elements for memory and logic units.In this proposal we will expand the fundamental understanding of the dynamic nature of the coupling of the chiral CDW with femtosecond optical perturbations and nanosecond current pulses. The dynamics of the excited metastable states through which the system traverses before coming back to equilibrium could include unconventional order such as ferroelectricity, CDW or superconductivity. The origin of these phenomena is in the existence of various types of symmetry breaking (inversion symmetry in TiSe2) that gives rise to degenerate ground states. The opportunity exists to exploit these metastable states in low power electronic devices. We will also optimize the growth of TiSe2 thin films in order to enable efficient device fabrication. The effect on strain and doping on chiral CDW thermodynamics will be explored.