Probing moire flat bands with optical spectroscopy

用光谱法探测莫尔平坦带

• 批准号: 2004474
• 负责人: Jun Yan
• 金额: $ 39.24万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2004474&HistoricalAwards=false
• 关键词: Probing; moire; flat; bands; optical

Nontechnical Description: When a layer with a periodic pattern is laid on top of another similar pattern with minor difference(s) in pitch or orientation, moiré interference patterns appear. Such moiré patterns can occur even at an atomic scale by slightly misaligning the stacking of two 2D (two-dimensional) crystals, which can dramatically modify the properties of the atomic stacks. For example, on its own, graphene (a layer of carbon a single atom thick) conducts electricity like metal does, but with a moiré pattern it can behave either like plastics which don’t conduct electricity or like a superconductor which conducts electricity without generating any heat. This research investigates the unusual behaviors of electronic structures due to moiré patterns. Knowledge acquired through this study will reveal fundamental properties of moiré-patterned 2D systems and pave the way for developing devices that make use of these surprising phenomena. Beyond scientific and technological impacts, this project brings modern materials physics education to the broader Western Massachusetts community through workshops and lab visits. A new summer research internship will be established in collaboration with a Hispanic-serving regional community college, to provide promising underrepresented minority students with a science research experience in the principle investigator’s 2D materials lab. The objective of this internship is to provide educational enrichment opportunities and increase access to science careers to students who are traditionally underrepresented, so that they will be better prepared for matriculating into a four-year institution and later to graduate schools.Technical Description: Moiré superlattices with relatively long wavelength of ~10nm in 2D crystals can create almost dispersionless electronic bands, where the kinetic energies of the charges are strongly suppressed, giving way to Coulomb interaction that drives strongly correlated phases. In this project, the PI uses versatile optical spectroscopy techniques to investigate these moiré flat bands formed in stacked atomic layers of graphene and transition metal dichalcogenides. Quantum states such as Mott insulators, superconductivity, and Chern insulators are continuously tuned by the electric fields. Fundamental properties of these states are probed by measuring exciton polarons, magneto-phonon resonances and electronic Raman susceptibility. This project advances scientific knowledge of the quantum materials physics by focusing on three main questions regarding the nature of the moiré flat bands: 1) What is the size and nature of the spontaneously opened gaps in partially filled moiré bands? 2) Can the interaction break the spin and valley degeneracy in the absence of an external magnetic field, and what is the spin and valley polarization? 3) What kind of novel excitations can the correlated states host? Understanding and tuning these properties by the electric field effect are important not only for fundamental physics, but also for future device applications harnessing these unusual properties.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.

非技术描述：当一个具有周期性图案的层被放置在另一个在间距或方向上有微小差异的相似图案上时，就会出现波纹干涉图案。即使在原子尺度上，只要将两个二维（二维）晶体的堆叠稍微错位，就可以产生这种莫尔条纹，这可以极大地改变原子堆叠的性质。例如，石墨烯（一层单原子厚度的碳）本身就能像金属一样导电，但它的莫尔纹图案既可以像不导电的塑料一样，也可以像不产生任何热量的超导体一样导电。本研究探讨了由波纹模式引起的电子结构的异常行为。通过这项研究获得的知识将揭示莫尔梅格纹二维系统的基本特性，并为开发利用这些令人惊讶的现象的设备铺平道路。除了科学和技术的影响，该项目通过研讨会和实验室参观，将现代材料物理教育带到更广泛的马萨诸塞州西部社区。将与一所拉美裔地区社区学院合作建立一个新的暑期研究实习项目，为有前途的少数族裔学生提供在首席研究员的2D材料实验室进行科学研究的机会。这次实习的目的是为传统上代表性不足的学生提供丰富的教育机会，增加他们从事科学职业的机会，以便他们为进入四年制大学和后来的研究生院做好更好的准备。技术描述：二维晶体中波长相对较长的~10nm的moir<s:1>超晶格可以产生几乎无色散的电子带，其中电荷的动能被强烈抑制，让位于驱动强相关相的库仑相互作用。在这个项目中，PI使用多功能光学光谱技术来研究这些在石墨烯和过渡金属二硫族化合物的堆叠原子层中形成的波纹平坦带。量子态如莫特绝缘体、超导绝缘体和陈氏绝缘体是由电场连续调谐的。通过测量激子极化子、磁声子共振和电子拉曼磁化率来探测这些态的基本性质。本项目通过关注三个关于莫尔条纹平坦带性质的主要问题来推进量子材料物理的科学知识：1)在部分填充的莫尔条纹中自发打开的间隙的大小和性质是什么？2)在没有外加磁场的情况下，相互作用能否打破自旋和谷简并，什么是自旋和谷极化？3)相关态能承载什么样的新激励？通过电场效应理解和调整这些特性不仅对基础物理学很重要，而且对利用这些不寻常特性的未来设备应用也很重要。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。

项目成果

Enhancement of exciton valley polarization in monolayer MoS2 induced by scattering

• DOI: 10.1103/physrevb.104.l121408
• 发表时间: 2021-09
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Yueh-Chun Wu;T. Taniguchi;Kenji Watanabe;Jun Yan

Axial Higgs mode detected by quantum pathway interference in RTe3

• DOI: 10.1038/s41586-022-04746-6
• 发表时间: 2021-12
• 期刊: Nature
• 影响因子: 64.8
• 作者: Yiping Wang;Ioannis Petrides;G. McNamara;Md Mofazzel Hosen;Shiming Lei;Yueh-Chun Wu;J. Hart;H. Lv;Jun Yan;Di Xiao;J. Cha;P. Narang;L. Schoop;K. Burch

Probing the bright exciton state in twisted bilayer graphene via resonant Raman scattering

• DOI: 10.1063/5.0049458
• 发表时间: 2021-07-05
• 期刊: APPLIED PHYSICS LETTERS
• 影响因子: 4
• 作者: DeCapua, Matthew C.;Wu, Yueh-Chun;Yan, Jun
• 通讯作者: Yan, Jun

Negative valley polarization in doped monolayer MoSe 2

掺杂单层 MoSe 2 中的负谷极化

• DOI: 10.1039/d1cp03490a
• 发表时间: 2021
• 期刊: Physical Chemistry Chemical Physics
• 影响因子: 3.3
• 作者: Wu, Yueh-Chun;Taniguchi, Takashi;Watanabe, Kenji;Yan, Jun
• 通讯作者: Yan, Jun