近日，中国人民大学的于伟强教授课题组与中国科学院物理研究所的Anders W. Sandvik等人合作并取得一项新进展。经过不懈努力，他们发现了SrCu₂(BO₃)₂中的近似去禁闭量子临界点。相关研究成果已于2023年5月25日在国际权威学术期刊《科学》上发表。

该研究团队利用高压¹¹B核磁共振测量技术在量子磁体SrCu₂(BO₃)₂上演示了在极低温度（临界转换温度T_c≈0.07K）条件下，磁场诱导压强超过1.8 GPa时plaquette-singlet态到反铁磁态的相变。随着压力增加，相变的一阶特征逐渐减弱，并且研究人员观察到在最高压力2.4 GPa下的量子临界尺度。在模型计算的支持下，他们认为这些观察结果可以通过近似DQCP诱导临界量子涨落和有序参数的新生O(3)对称性来解释。该研究的发现为DQCP的研究提供了具体的实验平台。

据了解，去禁闭量子临界点（DQCP）代表了量子物质研究中的一个范式转变，提供了一种超越朗道场景的有序-有序转换。然而，实现该点的实验一直以来一直非常具有挑战性。

附：英文原文

Title: Proximate deconfined quantum critical point in SrCu₂(BO₃)₂

Author: Yi Cui, Lu Liu, Huihang Lin, Kai-Hsin Wu, Wenshan Hong, Xuefei Liu, Cong Li, Ze Hu, Ning Xi, Shiliang Li, Rong Yu, Anders W. Sandvik, Weiqiang Yu

Issue&Volume: 2023-05-25

Abstract: The deconfined quantum critical point (DQCP) represents a paradigm shift in quantum matter studies, presenting a “beyond Landau” scenario for order–order transitions. Its experimental realization, however, has remained elusive. Using high-pressure ¹¹B nuclear magnetic resonance measurements on the quantum magnet SrCu ₂(BO ₃) ₂, we here demonstrate a magnetic-field induced plaquette-singlet to antiferromagnetic transition above 1.8 GPa at a notably low temperature, Tc0.07K. First-order signatures of the transition weaken with increasing pressure, and we observe quantum critical scaling at the highest pressure, 2.4 GPa. Supported by model calculations, we suggest that these observations can be explained by a proximate DQCP inducing critical quantum fluctuations and emergent O(3) symmetry of the order parameters. Our findings offer a concrete experimental platform for the investigation of the DQCP.

DOI: adc9487

Source: https://www.science.org/doi/10.1126/science.adc9487