Interference of quantum critical excitations and soft diffusive modes in a disordered antiferromagnetic metal
Interference of quantum critical excitations and soft diffusive modes in a disordered antiferromagnetic metal
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DOI：
10.1103/physrevb.93.045128
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发表时间：
2015-07
影响因子：
3.7
通讯作者：
Philipp S. Weiss;B. Narozhny;J. Schmalian;P. Wolfle
中科院分区：
文献类型：
--
作者：
Philipp S. Weiss;B. Narozhny;J. Schmalian;P. Wolfle
研究了二维金属在反铁磁（AFM）量子临界点附近的自旋密度涨落和弱无序相互作用对电导率的温度相关量子修正。AFM自旋密度波动在有序向量$\mathbf{Q}$周围携带着很大的动量，并且在自旋-费米子耦合的最低阶，只在费米表面的热点之间散射电子，这些热点由$\mathbf{Q}$连接。早先，我们发现AFM自旋密度波动和无序金属的软扩散模式之间的量子干涉被抑制，这是大动量散射的结果。抑制这种干扰导致相应的相互作用修正对电导率的非奇异温度依赖。然而，在高阶自旋-费米子耦合下，整个费米表面上的电子可以通过两次自旋密度波动而连续散射，并且总的动量转移很小。这种高阶过程可以用带有小动量的复合模态来描述。结果表明，在低温条件下，复合模和扩散模之间的干涉产生了奇异的相互作用修正，最终超过了非奇异的一阶修正。我们从自旋-费米子模型推导了一个有效的低能理论，该理论隐含了上述高阶过程，并证明了弱自旋-费米子耦合的小动量传递是由复合传播子介导的。采用传统的图解方法对杂质散射，我们发现修正$\delta \sigma \sim +\ln^2 T$温度高于指数小的交叉尺度。
We study the temperature-dependent quantum correction to conductivity due to the interplay of spin density fluctuations and weak disorder for a two-dimensional metal near an antiferromagnetic (AFM) quantum critical point. AFM spin density fluctuations carry large momenta around the ordering vector $\mathbf{Q}$ and, at lowest order of the spin-fermion coupling, only scatter electrons between "hot spots" of the Fermi surface which are connected by $\mathbf{Q}$. Earlier, it was seen that the quantum interference between AFM spin density fluctuations and soft diffusive modes of the disordered metal is suppressed, a consequence of the large-momentum scattering. The suppression of this interference results in a non-singular temperature dependence of the corresponding interaction correction to conductivity. However, at higher order of the spin-fermion coupling, electrons on the entire Fermi surface can be scattered successively by two spin density fluctuations and, in total, suffer a small momentum transfer. This higher-order process can be described by composite modes which carry small momenta. We show that the interference between formally subleading composite modes and diffusive modes generates singular interaction corrections which ultimately dominate over the non-singular first-order correction at low temperatures. We derive an effective low-energy theory from the spin-fermion model which includes the above-mentioned higher-order process implicitly and show that for weak spin-fermion coupling the small-momentum transfer is mediated by a composite propagator. Employing the conventional diagrammatic approach to impurity scattering, we find the correction $\delta \sigma \sim +\ln^2 T$ for temperatures above an exponentially small crossover scale.