Congratulations to Professor Meng for winning the 2024 Top China Cited Paper Award (Physics)

Our team was one of the winners of the 2024 Top China Cited Paper Award (Physics) for "Momentum Space Quantum Monte Carlo on Twisted Bilayer Graphene", published in Chinese Physics Letters. This award for China-based authors is given to the top ten papers in the top 1% of the most cited articles published in IOP Publishing journals over the past three years (2021 – 2023). This data is from the citations recorded in Web of Science. This article (Chin. Phys. Lett. 38, 077305 (2021)) has developed a momentum space quantum Monte Carlo algorithm to deal with the long-range Coulomb interaction problem that emerges in two-dimensional quantum moire materials such as twisted graphene, which is one of the universal challenges in correlated electron systems. Three years ago, Zi Yang quoted the famous poetry of ancient Chinese poet Jiang Kui(姜夔) to explain how the “Coulomb force is endless, momentum Monte Carlo sends longing thoughts”(库伦作用无尽期,动量蒙卡寄相思) inspire them to pursue the research of long range interaction in quantum moire systems. The quantum many-body paradigm of the moire system is becoming a beautiful stream that carries them to the heartland of scientific creativity.

Dimensionality crossover to a 2D vestigial nematic state from a 3D antiferromagnet in a honeycomb van der Waals magnet

A collaboration between theoretical physicists Dr. Chengkang Zhou and Professor Zi Yang Meng from the Department of Physics at The University of Hong Kong (HKU), along with experimentalists Dr. Zeliang Sun, Professors Kai Sun and Liuyan Zhao from the Department of Physics at the University of Michigan, and Professor Rui He from the Department of Electrical and Computer Engineering at Texas Tech University, has led to a significant discovery in quantum physics. Their study was published in a recent issue of Nature Physics (Nat. Phys. (2024)). The research team was the first to experimentally observe a transition from a 3-dimensional (3D) long-range order state to a 2-dimensional (2D) flat pattern vestigial order state in NiPS3. The vestigial order can be seen as the retention during the process of symmetry breaking. This occurs when the primary magnetic long-range order state breaks down into a simpler form - in this case, a 2D vestigial order state (known as Z3 Potts-nematicity) - as the NiPS3 material is thinned. The collaboration between the large-scale Monte Carlo simulation and the experiments led to this discovery during the dimension crossover process. Continue reading.

有时,科研也可以像一圈麻将

最近也有这样几个充满希望的青年人,在我身边学习和工作了几年之后,也要开始各自人生的下一个阶段。机缘巧合,整理了几块定制的麻将,做为鼓励他们走上人生的下一个阶段的礼物。想要表达的,其实是希望我们大家都不要落入文化和历史基因的循环,不要被科举制度的死灰复燃所迷惑。要记得人的自证(希腊),人的觉醒(文艺复兴),人与人的存在关系(美好年代),把创造性的能量发挥到极点,这样的历程在我们身在的环境中还远没有完成,还需要我们一起完成。Continue reading

Bye, Mr. Zhang

Congratulations from Zi Yang:

August 6, 2024, is a significant day for Mr. Xu Zhang, as on this day he has successfully defended his Ph.D. thesis with the title “Electromagnetic response in two dimensional flat band systems”. He has greatly impressed the Examining Committee comprised of Profs. Xi Dai and Ning Wang from HKUST and Profs. Wang Yao and Dong-Keun Ki from HKU, in clearly presenting the major research outputs during his Phd years in HKU, as well as addressing the interesting questions spontaneously appeared during the defense. Congratulations to Dr. Xu Zhang! And hope him a successful next step and becomes the next rising star in theoretical condensed matter physics. Continue reading

Spectral evidence for Dirac spinons in a kagome lattice antiferromagnet

A collaboration between theoretical physicists Dr. Chengkang ZHOU and Professor Zi Yang MENG from the Department of Physics at The University of Hong Kong (HKU), along with experimentalists Mr. Zhenyuan ZENG and Professor Shiliang LI at the Institute of Physics (IOP), Chinese Academy of Sciences (CAS), and Professor Kenji NAKAJIMA from J-PARC Center, Japan, has led to a discovery in the realm of quantum physics. Their study, published in a recent issue of Nature Physics ( Nat. Phys. 20, 1097–1102 (2024)), sheds light on the long-anticipated emergence of quasiparticles, akin to the famous Dirac particles obeying the relativistic Dirac equation. These quasiparticles, known as Dirac spinons, were theorised to exist within a novel quantum state called a quantum spin liquid state. This work captures the conic spin excitations arising from Dirac spinons, resulting in low-energy spin excitations with sharp energy-momentum characteristics. Their results provide strong evidence for the emergence of a Dirac quantum spin liquid state in YCu3-Br. Continue reading

亚得里亚海边的回忆

科学事业的传承,创造性精神的传承,在我们的文化基因中是如此地难能可贵,过去的十年,二十年,三十年,似乎在我们的历史上成为了偶然,而如今的我们却必然地向着科举之下的干谒、八股和满街的勋宗们靠近,离玻尔兹曼、乔伊斯、茨维格和人类群星闪耀着的的里雅斯特的美好年代,离亚得里亚海边柔和的晚风和灯光越来越远。Continue reading

New paradigm of quantum phase transitions discovered from entanglement measurements

How does matter acquire mass? It's a question of fundamental importance to physicists. Traditionally, we've understood that all matter in the universe gains mass through a process called spontaneous symmetry breaking. Yet, recent discoveries in both condensed matter and high-energy physics have unveiled a new mechanism of mass generation without any symmetry breaking, known as "symmetric mass generation" (SMG). In our current work, we set out to investigate whether SMG corresponds to a true continuous phase transition with universal behaviors. Using newly developed numerical probes of quantum entanglement, we delved into the heart of this phenomenon on interacting electrons on honeycomb lattice, which might find its relevance in quantum moire materials. What we discovered is that, the SMG transition is indeed a continuous phase transition, but it defies all traditional paradigms. This finding opens up exciting avenues for understanding the fundamentally new mechanism of the mass generation. This work is published on Phys. Rev. Lett. 132.156503 (2024).

旧锦新样 | 寂静春天里的动力学

在这样混乱嘈杂的春天里,哪里能找到寂静,哪里能找到新的生机酝酿时静默却不可阻挡的力量,是考验从业人员实力、修为和气魄的大问题。春天当然是动态的,但是动态要有一个静的表面,新发现孕育的时候如林间的野花幼苗,阳光雨露之下静却决绝。一开始就熙熙攘攘热热闹闹,混淆了心智,耗尽了力气,怎么可能看到成熟和收获呢? 就是在这样的考虑之下,笔者和朋友们决定在凝聚态物理学量子多体计算的领地中,在这个春天里培育一株幼苗,小心地浇灌它,期望它成长为凝聚态物理学量子多体计算领地中的大树。这株幼苗,就是量子多体系统的动力学性质计算。 Continue reading

旧锦新样 | 百年孤独和一级相变


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 [Commun Phys 7, 207 (2024)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

Unearth the myth in long-range interacting systems

Recent research demystifies the effects of long-range interactions on physical systems. Our quantum Monte Carlo simulations and field theoretical analysis on (2+1)-dimensional O(3) quantum critical points and two-dimensional Néel states with long-range interactions have uncovered the critical exponents of quantum critical points influenced by long-range interactions exhibit three distinct renormalization group fixed points [Phys. Rev. B 109, L081114 (2024) Editor's suggestion]. At finite temperature, our unbiased investigation demonstrated the spontaneous breaking of SU(2) symmetry in Heisenberg model with 1/r^α-form long-range interactions beyond the Mermin-Wagner theorem. Critical exponents have been determined for different ranges of α, revealing new critical behaviors [npj Quantum Mater. 8, 59 (2023)]. These works encourage further theoretical and experimental studies of quantum materials with long-range interactions, expanding our understanding beyond locality.