Sr3Ru2O7：量子临界金属中相形成的热力学
Sr3Ru2O7: Thermodynamics of Phase Formation in a Quantum Critical Metal
摘要：
物质在零温附近连续相变的行为，或称“量子临界点”（QCP），是凝聚态物理研究的中心课题。在费米子系统中，基本的问题仍然没有答案：量子临界区的性质是不清楚的，因为准粒子的概念明显崩溃，强相互作用金属的现有理论的基石。甚至更少的是已知的实验形成有序相从这样的量子临界“汤”。在这里，我们报告的比热跨模型系统Sr3Ru2O7的相图的研究，其特征在于一个异常的相，其传输特性是一致的，与那些的电子的电子相变。我们表明，这一阶段，它存在于低温下在一个狭窄的范围内的磁场，直接从量子临界态的形式，并包含更多的熵比平均场计算预测。我们的结果表明，这种额外的熵是由于剩余自由度的高熵态以上的T_c。相关联的量子临界点，这是“隐藏”的相，分离两个费米液体，其中没有一个具有可识别的自发破缺对称性，但可能不同的拓扑结构的费米表面。
英文摘要：
The behaviour of matter near zero temperature continuous phase transitions, or 'quantum critical points' (QCPs) is a central topic of study in condensed matter physics. In fermionic systems, fundamental questions remain unanswered: the nature of the quantum critical regime is unclear because of the apparent breakdown of the concept of the quasiparticle, a cornerstone of existing theories of strongly interacting metals. Even less is known experimentally about the formation of ordered phases from such a quantum critical 'soup'. Here, we report a study of the specific heat across the phase diagram of the model system Sr3Ru2O7, which features an anomalous phase whose transport properties are consistent with those of an electronic nematic. We show that this phase, which exists at low temperatures in a narrow range of magnetic fields, forms directly from a quantum critical state, and contains more entropy than mean-field calculations predict. Our results suggest that this extra entropy is due to remnant degrees of freedom from the highly entropic state above T_c. The associated quantum critical point, which is 'concealed' by the nematic phase, separates two Fermi liquids, neither of which has an identifiable spontaneously broken symmetry, but which likely differ in the topology of their Fermi surfaces.
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