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arXiv 1601.03403cond-mat.str-el
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二维金属中的量子临界涨落:反铁磁体和铜氧化物中的奇异金属和超导性

Quantum-Critical Fluctuations in 2D Metals: Strange Metals and Superconductivity in Antiferromagnets and in Cuprates

Chandra M. Varma

摘要:

量子临界区、铜氧化物、准二维铁基超导体和重费米子化合物的反常输运和热力学性质具有相同的温度依赖性。尽管它们有巨大的微观差异,但只有当一个共同的统计力学模型描述它们的相变时,才能发生这种情况。反铁磁(AFM)IC模型为后两个,就像环电流模型的铜酸盐,映射到耗散XY模型。这个模型在2+ 1D中的解揭示了临界涨落是由拓扑激发、涡旋和各种瞬子决定的,而不是由Landau-Ginzburg-Wilson类型的重整化自旋波理论决定的,后者由Moriya、Hertz和其他人改编为量子临界性。吸收部分的波动是一个可分离的功能的动量${\bf q}$,测量的顺序矢量,和频率$ω$和温度$T$的规模为$\tanh(ω/2T)$在临界状态。在准二维重费米子和铁基化合物的反铁磁量子临界点附近,通过中子散射直接测量的涨落与这种形式是一致的。这样的涨落,加上把它们耦合到费米子的顶点,导致了边缘费米液体,对所有动量都有自能的虚部$\propto max(ω, T)$,电阻率$\propto T$,对比热的贡献$T \ln T$,以及这些不同化合物共有的其他奇异费米液体性质,以及d波超导性。这在铜酸盐中通过分析从最近的高分辨率角分辨光电子能谱测量中直接提取的配对和正常自能得到了明确的验证。

英文摘要:

The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in 2+1 D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum ${\bf q}$, measured from the ordering vector, and of the frequency $ω$ and the temperature $T$ which scale as $\tanh(ω/2T)$ at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy $\propto max(ω, T)$ for all momenta, a resistivity $\propto T$, a $T \ln T$ contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements.

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