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: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=690188
• 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共同创造出新的、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，如手性p波。它们可能是电荷、自旋或对密度波，这些特性的周期性调制共存于所谓的“赝隙态”中，赝隙态是产生高Tc超导性的母态。超导体是由库柏对组成的，库柏对是被束缚的电子对，它们凝聚成超流体。手性超导体是指库珀对全部顺时针或逆时针旋转，从而打破时间反转对称性的超导体。手性超导体具有独特的激发态，马约拉纳费米子的作用就像半个电子，分数涡旋的不寻常性质原则上可以在量子计算中得到利用。我研究的一个体系，Sr2RuO4，被认为是一个手性p波超导体，p波意味着库珀对的角动量为1。这样的系统应该表现出尚未被观察到的自发表面超流，我的部分研究涉及理解为什么不能或如何才能观察到它们。可能还有其他的手性超导体，比如UPt3，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强磁场中的高温超导体。物理学家们惊讶地发现，高温超导体中的量子振荡是磁场的函数，因为人们认为这些振荡在这些材料中的强相互作用中不会存在。此外，观测到的量子振荡频率也不像预期的那样；由于静态密度波，费米表面似乎被“重建”了。那么问题是这些密度波是在电荷中，自旋中还是在库珀对波函数中？我的目标是加深我们对新型对密度波态的理解，更一般地说，是对高温超导体的理解。******这种研究对加拿大的影响和重要性可以用一个例子来最好地说明。20世纪90年代初，我和一个本科生乔迪·罗斯（Geordie Rose）一起研究d波超导，他后来在不列颠哥伦比亚大学（UBC）攻读了另一个学科的博士学位，后来在不列颠哥伦比亚省创办了一家公司——d波系统公司（d-wave Systems），这是世界上第一家量子计算公司。现在我正在研究其他新现象，马约拉纳费米子和对密度波超导。我的大多数学生将在基础研究、金融建模或利用大型数据集的研究方面走传统的道路，加拿大公司需要他们的高科技技能。少数人，因为他们研究的是全新的东西，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