Hu Ze, Ma Zhen, Liao Yuan-Da, Li Han, Ma Chunsheng, Cui Yi, Shangguan Yanyan, Huang Zhentao, Qi Yang, Li Wei, Meng Zi Yang, Wen Jinsheng, Yu Weiqiang
Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing, 100872, China.
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing, 210093, China.
Nat Commun. 2020 Nov 6;11(1):5631. doi: 10.1038/s41467-020-19380-x.
The Berezinskii-Kosterlitz-Thouless (BKT) mechanism, building upon proliferation of topological defects in 2D systems, is the first example of phase transition beyond the Landau-Ginzburg paradigm of symmetry breaking. Such a topological phase transition has long been sought yet undiscovered directly in magnetic materials. Here, we pin down two transitions that bound a BKT phase in an ideal 2D frustrated magnet TmMgGaO, via nuclear magnetic resonance under in-plane magnetic fields, which do not disturb the low-energy electronic states and allow BKT fluctuations to be detected sensitively. Moreover, by applying out-of-plane fields, we find a critical scaling behavior of the magnetic susceptibility expected for the BKT transition. The experimental findings can be explained by quantum Monte Carlo simulations applied on an accurate triangular-lattice Ising model of the compound which hosts a BKT phase. These results provide a concrete example for the BKT phase and offer an ideal platform for future investigations on the BKT physics in magnetic materials.
Berezinskii-Kosterlitz-Thouless（BKT）机制基于二维系统中拓扑缺陷的增殖，是超越朗道-金兹堡对称破缺范式的相变的首个例子。这种拓扑相变长期以来一直被寻找，但尚未在磁性材料中直接发现。在此，我们通过在面内磁场下的核磁共振，确定了理想二维受挫磁体TmMgGaO中界定BKT相的两个转变，该磁场不会干扰低能电子态，并能灵敏地检测到BKT涨落。此外，通过施加面外磁场，我们发现了BKT转变预期的磁化率临界标度行为。实验结果可以通过应用于具有BKT相的化合物的精确三角晶格伊辛模型的量子蒙特卡罗模拟来解释。这些结果为BKT相提供了一个具体例子，并为未来对磁性材料中BKT物理的研究提供了一个理想平台。
