Ferromagnetic Quantum Critical Point in the Heavy-Fermion Metal YbNi4(P1−xAsx)2
Ferromagnetic Quantum Critical Point in the Heavy-Fermion Metal YbNi4(P1−xAsx)2
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DOI：
10.1126/science.1230583
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发表时间：
2013-02
期刊：
影响因子：
56.9
通讯作者：
A. Steppke;R. Küchler;S. Lausberg;E. Lengyel;L. Steinke;R. Borth;T. Lühmann;C. Krellner;M. Nickla
中科院分区：
文献类型：
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作者：
A. Steppke;R. Küchler;S. Lausberg;E. Lengyel;L. Steinke;R. Borth;T. Lühmann;C. Krellner;M. Nickla
量子临界点（QCP）发生在量子涨落（即使在绝对零度下也不会消失）导致逐渐（所谓的二阶）相变时。在铁磁体中已经观察到了QCP，但对于铁磁金属，证据并不那么明确，人们认为，随着温度的降低，另一种秩序-如超导性-将阻止QCP的形成。然而，Steppke等人（第933页）使用比热和磁化率测量，在准一维重费米子材料YbNi 4（P1−xAsx）2中发现了强有力的证据，在砷替代水平约为10%的情况下，QCP存在。这些结果对铁磁体的量子临界性理论提出了挑战。精确的低温测量揭示了铁磁金属中与量子临界性相关的发散。非常规的超导性和其他以前未知的物质相存在于量子临界点（QCP）附近：绝对零度下物质的连续相变。对巡回系统的深入理论和实验研究表明，金属铁磁体倾向于通过一级相变或通过形成中间超导或不均匀磁相来发展。在这里，通过精密的低温测量，我们表明，重费米子金属铁磁体YbNi 4（P0.92As0.08）2的格吕奈森比发散冷却到T = 0时，表明铁磁QCP。我们观察到这种在d电子金属中被禁止的不稳定性在重费米子系统中发生，这将对量子临界材料的研究产生很大的影响。
Arsenic Makes a Difference A quantum critical point (QCP) occurs when quantum fluctuations, which do not go away even at absolute zero, cause a gradual (so-called second order) phase change. QCPs have been observed in ferromagnets, but for ferromagnetic metals, the evidence is less clear-cut and it is thought that, as the temperature is lowered, another order—such as superconductivity—will prevent the formation of a QCP. However, Steppke et al. (p. 933), using specific heat and magnetic susceptibility measurements, found strong evidence for a QCP in a quasi–one-dimensional heavy fermion material, YbNi4(P1−xAsx)2, near an Arsenic substitution level of about 10%. The results present a challenge to theories about quantum criticality in ferromagnets. Precision low-temperature measurements reveal a divergence associated with quantum criticality in a ferromagnetic metal. Unconventional superconductivity and other previously unknown phases of matter exist in the vicinity of a quantum critical point (QCP): a continuous phase change of matter at absolute zero. Intensive theoretical and experimental investigations on itinerant systems have shown that metallic ferromagnets tend to develop via either a first-order phase transition or through the formation of intermediate superconducting or inhomogeneous magnetic phases. Here, through precision low-temperature measurements, we show that the Grüneisen ratio of the heavy fermion metallic ferromagnet YbNi4(P0.92As0.08)2 diverges upon cooling to T = 0, indicating a ferromagnetic QCP. Our observation that this kind of instability, which is forbidden in d-electron metals, occurs in a heavy fermion system will have a large impact on the studies of quantum critical materials.