Theory of Quantum Materials

量子材料理论

• 批准号: RGPIN-2016-04598
• 负责人: Kallin, Catherine
• 金额: $ 3.64万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=615171
• 关键词: Theory; Quantum; Materials

My research is on “quantum materials” where the laws of quantum mechanics conspire with strong interactions to create new and interesting states of matter. These might be new kinds of superconductors, such as high temperature superconductors, or superconductors with complex internal structure such as chiral p-wave. They might be charge, spin or pair density waves, periodic modulations of these properties that coexist in the so-called “pseudogap state” which is the parent state from which high Tc superconductivity arises. Superconductors are made up of Cooper pairs, bound pairs of electrons that condense into a superfluid. A chiral superconductor is one in which the Cooper pairs all spin together clockwise or counter-clockwise, breaking time reversal symmetry. Chiral superconductors have distinctive excitations, Majorana fermions which act like half an electron, and fractional vortices, whose unusual properties can, in principle, be exploited in quantum computing. One system that I study, Sr2RuO4, is thought to be a chiral p-wave superconductor, where p-wave means that the Cooper pairs have angular momentum 1. Such a system should exhibit spontaneous surface supercurrents that have not yet been observed, and part of my research concerns understanding why not or how can they be observed. There may be other chiral superconductors, such as UPt3, and I am working on a theory to describe this system. Another thrust of my research is on high Tc superconductors in high magnetic fields. Physicists were surprised to observe quantum oscillations in high Tc superconductors as a function of magnetic field because it was thought that these oscillations would not survive the strong interactions in these materials. Also the quantum oscillation frequencies that were observed were not as expected; it appeared that the Fermi surface had been “reconstructed” due to static density waves. The question then is are these density waves in the charge or spin or in the Cooper pair wave function itself? My goal is to deepen our understanding of novel pair density wave states and, more generally, of high temperature superconductors. The impact and importance for Canada of such research is best illustrated by an example. In the early 1990's I was studying d-wave superconductivity with an undergraduate student, Geordie Rose, who went on to do a PhD at UBC on a different subject and later to found a company, D-Wave Systems, the world's first quantum computing company, in B.C. Now I am studying other new phenomena, Majorana fermions and pair density wave superconductors. Most of my students will follow conventional paths in basic research or in financial modeling or research utilizing large data sets, where their high-tech skills are in demand by Canadian companies. A few, because they studied things that were completely new, will go on to do something genuinely new and different with the goal of creating new technologies and new companies.

我的研究方向是“量子材料”，量子力学定律与强相互作用相结合，创造出新的有趣的物质状态。这些可能是新型超导体，如高温超导体，或具有复杂内部结构的超导体，如手征p波。它们可能是电荷、自旋或对密度波，这些性质的周期性调制共存于所谓的“赝能隙态”，这是高Tc超导性产生的母态。 超导体是由库珀对组成的，库珀对是一对束缚在一起的电子，它们凝聚成超流体。手征超导体是一种库珀对都一起顺时针或逆时针旋转的超导体，打破了时间反演对称性。手征超导体有独特的激发，马约拉纳费米子的行为就像半个电子，分数涡旋，其不寻常的性质，原则上，可以在量子计算中利用。我研究的一个系统，Sr 2 RuO 4，被认为是手征p波超导体，其中p波意味着库珀对的角动量为1。这样一个系统应该表现出尚未被观察到的自发表面超电流，我的部分研究涉及理解为什么不能或如何观察到它们。可能还有其他的手性超导体，比如UPt 3，我正在研究一个理论来描述这个系统。 我研究的另一个重点是高磁场中的高温超导体。物理学家惊讶地观察到高Tc超导体中的量子振荡作为磁场的函数，因为人们认为这些振荡不会在这些材料中的强相互作用中幸存下来。此外，观测到的量子振荡频率并不像预期的那样;费米表面似乎是由于静态密度波而“重建”的。那么问题就来了，这些密度波是在电荷或自旋中，还是在库珀对波函数本身中？我的目标是加深我们对新型对密度波态的理解，更广泛地说，是对高温超导体的理解。 一个例子最能说明这种研究对加拿大的影响和重要性。在20世纪90年代初，我和一个本科生Geordie Rose一起研究d波超导性，他后来在UBC攻读了一个不同主题的博士学位，后来在BC成立了一家公司，世界上第一家量子计算公司D-Wave Systems。我的大多数学生将遵循传统的基础研究或金融建模或研究利用大型数据集，其中他们的高科技技能是由加拿大公司的需求路径。一些人，因为他们研究的是全新的东西，他们将继续做一些真正新的和不同的事情，目标是创造新技术和新公司。