Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
Science. 2011 Jan 21;331(6015):316-9. doi: 10.1126/science.1197531.
Fermi liquid theory, the standard theory of metals, has been challenged by a number of observations of anomalous metallic behavior found in the vicinity of a quantum phase transition. The breakdown of the Fermi liquid is accomplished by fine-tuning the material to a quantum critical point by using a control parameter such as the magnetic field, pressure, or chemical composition. Our high-precision magnetization measurements of the ultrapure f-electron-based superconductor β-YbAlB(4) demonstrate a scaling of its free energy that is indicative of zero-field quantum criticality without tuning in a metal. The breakdown of Fermi liquid behavior takes place in a mixed-valence state, which is in sharp contrast with other known examples of quantum critical f-electron systems that are magnetic Kondo lattice systems with integral valence.
费米液体理论是金属的标准理论，但在量子相变附近观察到的一些异常金属行为对其提出了挑战。通过使用磁场、压力或化学成分等控制参数将材料微调到量子临界点，可以实现费米液体的破坏。我们对基于超纯 f 电子的超导β-YbAlB(4)的高精度磁化测量表明，其自由能的标度表明在没有调谐的情况下存在零场量子临界点。费米液体行为的破坏发生在混合价态中，这与其他已知的量子临界 f 电子系统形成鲜明对比，后者是具有整数价的磁性 Kondo 晶格系统。
