近日，中国科学技术大学的潘建伟&陈宇翱及其研究团队取得一项新进展。经过不懈努力，他们观察到三维费米子哈伯德模型中的反铁磁相变。相关研究成果已于2024年7月10日在国际权威学术期刊《自然》上发表。

该研究团队观察到一个由锂-6原子组成的三维费米子哈伯德系统中的反铁磁相变，该系统在一个均匀的光学晶格中有大约80万个位点。当相互作用强度、温度和掺杂浓度被微调到接近各自的临界值时，研究人员观察到自旋结构因子急剧增加。这些观察结果可以用幂律发散来很好地描述，从海森堡普适性类来看，其临界指数为1.396。在半填充和最佳相互作用强度下，测得的自旋结构因子达到123(8)，表明了反铁磁相的建立。这项研究结果为探索FHM的低温相图提供了机会。

据悉，费米子哈伯德模型(FHM)描述了由强电子-电子关联性引起的广泛的物理现象，包括非常规超导的推测机制。然而，解析其低温物理问题在理论上或数值上都具有挑战性。光学晶格中的超冷费米子提供了一个干净且控制良好的平台，为模拟FHM提供了一条途径。在半填充状态下掺杂FHM模拟器的反铁磁基态有望产生各种奇异相，包括条纹序、赝隙和d波超流体，为高温超导性提供有价值的见解。虽然在短距离和长距离上已经观察到反铁磁相关，但反铁磁相尚未实现，因为它需要在大型均匀量子模拟器中足够低的温度。

附：英文原文

Title: Antiferromagnetic phase transition in a 3D fermionic Hubbard model

Author: Shao, Hou-Ji, Wang, Yu-Xuan, Zhu, De-Zhi, Zhu, Yan-Song, Sun, Hao-Nan, Chen, Si-Yuan, Zhang, Chi, Fan, Zhi-Jie, Deng, Youjin, Yao, Xing-Can, Chen, Yu-Ao, Pan, Jian-Wei

Issue&Volume: 2024-07-10

Abstract: The fermionic Hubbard model (FHM) describes a wide range of physical phenomena resulting from strong electron–electron correlations, including conjectured mechanisms for unconventional superconductivity. Resolving its low-temperature physics is, however, challenging theoretically or numerically. Ultracold fermions in optical lattices provide a clean and well-controlled platform offering a path to simulate the FHM. Doping the antiferromagnetic ground state of a FHM simulator at half-filling is expected to yield various exotic phases, including stripe order, pseudogap, and d-wave superfluid, offering valuable insights into high-temperature superconductivity. Although the observation of antiferromagnetic correlations over short and extended distances has been obtained, the antiferromagnetic phase has yet to be realized as it requires sufficiently low temperatures in a large and uniform quantum simulator. Here we report the observation of the antiferromagnetic phase transition in a three-dimensional fermionic Hubbard system comprising lithium-6 atoms in a uniform optical lattice with approximately 800,000 sites. When the interaction strength, temperature and doping concentration are finely tuned to approach their respective critical values, a sharp increase in the spin structure factor is observed. These observations can be well described by a power-law divergence, with a critical exponent of 1.396 from the Heisenberg universality class. At half-filling and with optimal interaction strength, the measured spin structure factor reaches 123(8), signifying the establishment of an antiferromagnetic phase. Our results provide opportunities for exploring the low-temperature phase diagram of the FHM.

DOI: 10.1038/s41586-024-07689-2

Source: https://www.nature.com/articles/s41586-024-07689-2