编者按：最近某次关于分数陈绝缘体相变问题的讨论，涉及到多体系统作用量三阶项会导致一级相变的故事，勾起笔者对一段往事的追怀，想起八年前这篇游戏文字。文字背后的物理现象是在阻挫三角晶格横场 Ising model 量子临界点上，作用量三阶项消失，QCP 展现 emergent continuous symmetry；而在阻挫六角晶格横场 Ising mode 的量子临界点上，作用量三阶项不消失，QCP 为一级相变。这个故事背后的研究论文是 [Phys. Rev. B 96, 115160 (2017)]。类似的故事，笔者和合作者最近研究三角晶格量子环路模型相图的工作中，亦有所体现 [arXiv:2205.04472 和 情愿不自由，便是自由了 | 量子多体中的呐喊与彷徨之十二]。不想如今这样的现象又在分数陈绝缘体相变问题中改头换面地出现。可见马尔克斯百年孤独的经典开头诚不我欺，“多年之后面对 ……” 这样的事情，在个人的生命历程中总是反复地出现，一如身处的环境总在重复其文化历史基因中的错误一样。值得记取的教训，除了马贡多小镇无法摆脱的悲剧宿命和多体系统作用量三阶项会导致一级相变，恐怕还是“学好蒙特卡洛，不会被忽悠”。 Continue reading
Author: Zi Yang Meng
JOIN US NOW: Post-doctoral Fellow
Post-doctoral Fellow in Computational and Theoretical Condensed Matter Physics in the Department of Physics
JOIN US NOW: Research Assistant Professor
Research Assistant Professor in Quantum simulation, 2D quantum materials, quantum many-body entanglement in the Department of Physics
Advanced computing system ‘Blackbody’ for solving the challenging physics problems
To pursue advances in astronomy, quantum physics, and interdisciplinary science, our research teams worked together to deploy a new supercomputing system, named ‘Blackbody’ supercomputer -- the name stems from their respective research topics of ‘Black hole’ and ‘Quantum many-body‘ physics. The system has been set up in fall 2022 and is currently in full operation. Thank you for the hard work and Congratulations for all the participants! Continue reading
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from Quantum Materials to the Origin of Black Holes
In the time of quantum technology and big data, scientists start to integrate Artificial Intelligence (AI) and computational approaches into the fundament research about our mother Nature and Universe. This series of two lectures will help us to unfold such interesting discovery processes. Dr Zi Yang MENG, Associate Professor at HKU Department of Physics, will explain the important role played by AI and computation in the modern quantum material research in the first lecture. Find more
无愁河上的浪荡汉子们
这个题目乍一看有点儿戏谑，甚至有些许少儿不宜的味道，其实《无愁河的浪荡汉子》是木刻家、画家、作家黄永玉在80多岁时开始写作的以自己为原型的人生自传，目前已经出到第三部。第一部《朱雀城》从传主张序子两岁开始，写他的太婆、爷爷、父亲母亲、姑姑和表叔们——其中一位表叔就是写出《边城》、《长河》和《中国古代服饰研究》的沈从文——一个大家族，和他们生活的朱雀古城(以湘西凤凰为原型)，古城的四季时光、风俗民情与繁华时的荣耀。 Continue reading
关于纠缠的十四行诗
十四行诗，英文叫Sonnet，老一辈翻译家还曾根据音译翻成商籁体，很好听。其实是欧洲的格律诗，最初是小诗、小歌谣，也不一定十四行，随着历史的演进十四行诗句的格式逐渐被定型下来，而且押韵结构也有了严格的限制。在文艺复兴时的意大利，有了彼特拉克体（Petrarchan Sonnet），音韵优美，以歌颂爱情为主。一般分为两部分，前一部分由两段四行诗组成，韵脚为a-b-b-a，a-b-b-a；后一部分由两段三行诗组成，韵脚为c-d-e，c-d-e。 Continue reading
转角石墨烯的三昧
三昧是佛教里的话，是说修行的人能够止息杂念，心神平静，进入禅定，一窥事物的真谛。我们这些俗人，又生活在俗世，每天都在吃喝拉撒中辗转，应付尚且不足，禅定更不可及，离三昧境盖益远矣。大先生有篇著名的文章，叫《世故三昧》，很短，很有趣，把在人世间难得三昧的窘境和苦境写得通透，感兴趣的读者可以找来看看，一定强过阅读下面带着公式和图表的物理八股。 Continue reading
我爱纠缠如秋裤
科学研究当然也是揭示规律性的活动，从事这个行业的，也颇有一些愿意思考的人。有趣的是，在笔者熟悉的量子多体系统的研究中，竟也存在一个和秋裤颇为相像的事物，揭示出量子多体系统中无处不在的量子纠缠这样深刻的道理，让科研从业者中愿意思考的人安心，忘却身边的种种不顺遂，进入“此中有真意”的境界而更加起劲地探索其中的奥妙。他们发现通过秋裤的视角可以揭示量子多体系统从朗道—金兹堡对称性自发破缺，到量子相变，再到拓扑序长程纠缠和范畴对称性等等奇异的现象，秋裤之功善莫大焉。 Continue reading
Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene
Twisted bilayer graphene (TBG) consists of two stacked layers of graphene rotated relative to one another. With a twist angle of about 1.10° the so-called “magic” angle, many unconventional electronic behaviors emerge, including superconductivity and correlated insulators, a type of insulating phase that arises from interactions between electrons. Elucidating the mechanism responsible for these electronic states in magic-angle TBG is a problem at the frontier of quantum materials research. To help solve this problem, we employ an unbiased quantum many-body numerical method (quantum Monte Carlo simulations) to investigate the possible insulating phases of TBG. Continue reading "Correlation-Induced Insulating Topological Phases at Charge Neutrality in Twisted Bilayer Graphene"