Low-dimensional quantum magnets promote strong correlations between magnetic moments that lead to fascinating quantum phenomena. A particularly interesting system is the antiferromagnetic spin-1/2 Heisenberg chain because it is exactly solvable by the Bethe-Ansatz method. It is approximately realized in the magnetic insulator copper pyrazine dinitrate, providing a unique opportunity for a quantitative comparison between theory and experiment. We investigate its thermodynamic properties with a particular focus on the field-induced quantum phase transition. Thermal expansion, magnetostriction, specific heat, magnetization, and magnetocaloric measurements are found to be in excellent agreement with exact Bethe-Ansatz predictions. Close to the critical field, thermodynamics obeys the expected quantum critical scaling behavior, and in particular, the magnetocaloric effect and the Grüneisen parameters diverge in a characteristic manner. Beyond its importance for quantum magnetism, our study establishes a paradigm of a quantum phase transition, which illustrates fundamental principles of quantum critical thermodynamics.

中文翻译：

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自旋1/2 Heisenberg链系统中的量子临界性吡嗪二硝酸铜。

低维量子磁体会促进磁矩之间的强相关性，从而导致引人入胜的量子现象。一个特别有趣的系统是反铁磁自旋1/2 Heisenberg链，因为它可以通过Bethe-Ansatz方法完全求解。在磁性绝缘子中，吡嗪酸亚硝酸铜近似实现，为理论和实验之间的定量比较提供了独特的机会。我们研究其热力学性质，特别关注场致量子相变。发现热膨胀，磁致伸缩，比热，磁化和磁热测量与精确的Bethe-Ansatz预测非常吻合。靠近临界场，热力学遵守预期的量子临界缩放行为，特别是，磁热效应和Grüneisen参数以特征性方式发散。除了对量子磁性的重要性外，我们的研究还建立了量子相变的范式，阐明了量子临界热力学的基本原理。