Thermal and electrical transport across a magnetic quantum critical point
Thermal and electrical transport across a magnetic quantum critical point
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DOI：
10.1038/nature11072
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发表时间：
2012-04
期刊：
影响因子：
64.8
通讯作者：
H. Pfau;S. Hartmann;U. Stockert;P. Sun;S. Lausberg;M. Brando;S. Friedemann;C. Krellner;C. Geibel-C.-G
中科院分区：
文献类型：
--
作者：
H. Pfau;S. Hartmann;U. Stockert;P. Sun;S. Lausberg;M. Brando;S. Friedemann;C. Krellner;C. Geibel-C.-G
当竞争相之间的连续跃迁在零温度下发生时，就会出现量子临界点（QCP）。磁性qcp的集体激发产生的金属性质与朗道费米-液体描述的预期大相径庭，这是金属中电子相关的标准理论。该理论的核心是准粒子的概念，即具有非相互作用电子量子数的电子激发。在这里，我们报告了在重费米子化合物YbRh2Si2中通过场感应磁QCP的热传输和电传输的测量（参考文献，）。我们证明了在零温度极限下，热传导率与电传导率的比值符合Wiedemann-Franz定律，在达到QCP的临界场以上的磁场中。这也适用于低于临界场的磁场，其中弱反铁磁秩序和费米液相形成于0.07 K以下（零场）。然而，在临界场，低温电导率超过导热率约10%，暗示非费米液体基态。这种对Wiedemann-Franz定律的明显违反为非常规类型的量子粒子提供了证据，在这种量子粒子中，朗道准粒子的基本概念不再成立。这些结果暗示朗道准粒子会分裂，而这种分裂的起源是与电子量子临界涨落相关的非弹性散射——这些见解可能与理解在各种相关材料中经常观察到的费米液体行为的其他偏差有关。
A quantum critical point (QCP) arises when a continuous transition between competing phases occurs at zero temperature. Collective excitations at magnetic QCPs give rise to metallic properties that strongly deviate from the expectations of Landau’s Fermi-liquid description, which is the standard theory of electron correlations in metals. Central to this theory is the notion of quasiparticles, electronic excitations that possess the quantum numbers of the non-interacting electrons. Here we report measurements of thermal and electrical transport across the field-induced magnetic QCP in the heavy-fermion compound YbRh2Si2(refs , ). We show that the ratio of the thermal to electrical conductivities at the zero-temperature limit obeys the Wiedemann–Franz law for magnetic fields above the critical field at which the QCP is attained. This is also expected for magnetic fields below the critical field, where weak antiferromagnetic order and a Fermi-liquid phase form below 0.07 K (at zero field). At the critical field, however, the low-temperature electrical conductivity exceeds the thermal conductivity by about 10 per cent, suggestive of a non-Fermi-liquid ground state. This apparent violation of the Wiedemann–Franz law provides evidence for an unconventional type of QCP at which the fundamental concept of Landau quasiparticles no longer holds,,. These results imply that Landau quasiparticles break up, and that the origin of this disintegration is inelastic scattering associated with electronic quantum critical fluctuations—these insights could be relevant to understanding other deviations from Fermi-liquid behaviour frequently observed in various classes of correlated materials.