Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA.
Nature. 2012 Sep 20;489(7416):379-84. doi: 10.1038/nature11406.
The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.
最著名的例子是玻色-爱因斯坦凝聚和超流性，它们已经在各种不同的系统中得到了实验验证。当玻色子相互作用时，无序会破坏凝聚，导致“玻色玻璃”。由于缺乏任何对称破缺和谱中不存在有限能隙，这种相在实验中非常难以捉摸。在这里，我们报告了在掺杂量子磁体（溴掺杂二氯四硫脲镍，DTN）中观察到的磁场诱导磁准粒子玻色玻璃。磁场中 DTN 的物理性质相当于正则系综中玻色子晶格气体的物理性质；溴掺杂会引入玻色子的跳跃和相互作用强度的无序，导致它们局域化为玻色玻璃，直至零场，此时它成为不可压缩的莫特玻璃。玻色玻璃（对应无能隙自旋液体）到玻色-爱因斯坦凝聚（对应磁有序相）的转变由控制临界温度随外加场标度的普遍指数标记，与理论预测非常吻合。我们的研究代表了对正则系综中无序玻色子的普遍特征的定量实验描述。
