Quasiparticles in Mott Insulators, Strange Metals and Spin liquids probed by Low Temperature Spectroscopic-Imaging Scanning Tunneling Microscopy

非技术摘要：当前凝聚态研究的一个令人兴奋的领域是参与输运的粒子与传统电子几乎没有相似之处的系统。一个例子是分馏，电子分裂成两个独立的部分；一部分携带电荷，另一部分携带自旋，正如预测在自旋液体中发生的那样。虽然这种分数粒子已经被假设存在了几十年，但关联在这种系统中通常很重要，这一事实使得理论处理变得困难。这一点再加上缺乏实验数据(分数量子霍尔效应除外)，减缓了进展。另一个例子是“奇怪的金属”，其传输性质表现出无法解释的行为。在这些材料中，电阻随温度线性变化，直到相当低的温度。到目前为止，对于这种线性电阻率还没有公认的理论。一些理论认为，这种现象可能是由于基本量子力学思想的崩溃，在一种粒子相互纠缠的状态下--这种现象被描述为“非粒子物理学”。因此，粒子在奇怪的金属相和自旋液体基态中的行为一直是凝聚态物理前沿的有趣问题。到目前为止，关于这些体系的大多数实验数据都是通过运输和其他大宗探针获得的，由于缺乏合适的样品等多种原因，关于这些体系的纳米级光谱数据很少。然而，在过去的几年里，一些已建立的Mott绝缘体被证明具有与奇怪的金属/自旋液体一致的行为，为它们的探索开辟了新的可能性。这个项目的目标是使用低温扫描隧道显微镜(STM)和光谱学(STS)来研究这种系统的物理。技术摘要：正在研究的材料包括：Sr3(RuxIr1-x)2O7体系和双层石墨烯(BLG)，在高温下输运显示出线性电阻率；1T-TaS2/1T-NbSe2单层和几层膜是Mott绝缘体，即使在高温下也可以实现自旋-液体相。扫描隧道显微镜的最大优点之一是可以探测真实的空间电子结构，同时获得动量空间(k-空间)色散的信息。通过将强大的准粒子干涉技术应用于这些材料类别，目标是获得光谱数据，这些数据将有助于区分不同的理论，并为这些难以捉摸的相的物理提供新的见解。最近关于自旋-液体的理论为电荷通道中的自旋特征提供了具体的预测，这使得现在是用扫描隧道显微镜研究这类系统的一个令人兴奋的时刻。该项目的成功将增强妇女和少数族裔在物理学方面的研究经验。正在开发的新课程将培训学生有关凝聚态的现代思想和技术。国际学生联合会的综合外展和教育活动将使有才华的高中生接触尖端科学。参与这些项目的学生将在当今研究的前沿接受材料和仪器方面的培训。这一奖项反映了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。

Non-technical Abstract: An exciting area of current condensed matter research is systems where the particles participating in transport bear little resemblance to conventional electrons. One example is fractionalization where electrons split into two separate pieces; one part carrying the charge and the other carrying the spin as is predicted to happen in spin liquids. While such fractional particles have been postulated to exist for many decades, the fact that correlations are usually important in such systems makes theoretical handling difficult. This combined with a lack of experimental data (with the exception of the fractional quantum Hall effect) has slowed progress. Another example of is that `strange metals’ where transport properties show unexplained behavior. In these materials, resistance varies linearly with temperature down to quite low temperatures. So far there is no accepted theory for this linear resistivity. Some theories have suggested that the phenomenon may result from the breakdown of basic quantum mechanical ideas, in a state where the particles become entangled with each other – a phenomenon described as “unparticle physics”. The behavior of particles in the strange metal phase and the spin liquid ground state, thus remain open interesting problems at the frontiers of condensed matter physics. So far, most experimental data on these systems has been obtained by transport and other bulk probes and there is very little nanoscale spectroscopic data on these systems due to multiple reasons including the dearth of suitable samples. In the last few years however, some of the established Mott insulators have been shown to exhibit behavior consistent with strange metals/spin liquids, opening up new possibilities for their exploration. The goal of this project is to use low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) to investigate the physics of such systems. Technical Abstract:The materials being studied include the Sr3(RuxIr1-x)2O7 system and bilayer graphene (BLG) where transport shows linear resistivity up to high temperatures; and 1T-TaS2/1T-NbSe2 monolayer- and few-layer films which are Mott insulators where the spin-liquid phase may be realized even at high temperatures. One of the biggest advantages of STM is that one can probe the real space electronic structure and obtain simultaneous information on momentum-space (k-space) dispersion. By applying powerful technique of quasiparticle interference to these materials classes, the goal is to obtain spectroscopic data that will help distinguish between different theories and provide new insights into the physics of these elusive phases. Recent theory on spin-liquids has provided concrete predictions for signatures of spinons in the charge channel which makes this an exciting time to study such systems with STM. The success of the project will enhance the research experience for women and minorities in physics. The new course being developed will train students in modern ideas and techniques in condensed matter. The PI's integrated outreach and education activities will expose talented high school students to cutting edge science. The students working on these projects will be trained on materials and instruments at the forefront of today’s research.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.