Competition between phonon superconductivity and Kondo screening in mixed valence and heavy fermion compounds
Competition between phonon superconductivity and Kondo screening in mixed valence and heavy fermion compounds
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DOI：
10.1103/physrevb.71.214521
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发表时间：
2005-06
影响因子：
3.7
通讯作者：
V. Barzykin;L. Gor’kov
中科院分区：
文献类型：
--
作者：
V. Barzykin;L. Gor’kov
利用周期Anderson模型的唯象方法，研究了重费米子超导体和混合价超导体中近藤效应和S波超导电性的竞争。与已知的超导体中单杂质近藤效应的结果类似，我们发现在重费米子超导体中，在较窄的模型参数和电子浓度范围内，存在超导转变温度重入区的主要可能性。在混合价超导体中，${T}_{c}$的抑制作用要弱得多。我们的理论在低温费米液体区具有最大的正确性，没有重入行为。为了检验它的适用性，我们对${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Ru}}_{3}{\mathrm{Si}}_{2}$中的${T}_{c}$的$x$依赖关系进行了拟合，得到了与实验数据很好的一致性，尽管在这种情况下没有发现再入。根据理论分析，对其他实验数据进行了讨论。特别是，我们比较了一些已知同系物的超导转变温度，即含有和不含有$f$元素的模拟周期晶格化合物。对于少数同系物，超导电性只存在于重费米子材料中，从而证实了后者超导机制的独特性。我们认为，对于其他一些化合物，如果超导电性主要起源于一些轻费米面，但在另一个费米面上产生了相当大的超导带隙，那么在两个同系物中，{T}{c}$的值可能保持相同的数量级，对此杂化或其他重费米子效应更为显著。通过传递，我们引用了旧的结果，表明在转变时比热的跳跃反映了费米表面上载流子的重量，而与导致超导的机制无关。
We consider competition of the Kondo effect and $s$-wave superconductivity in heavy fermion and mixed valence superconductors, using the phenomenological approach for the periodic Anderson model. Similar to the well known results for the single-impurity Kondo effect in superconductors, we have found the principal possibility of a reentrant regime of the superconducting transition temperature, ${T}_{c}$, in heavy fermion superconductors in a narrow range of model parameters and concentration of $f$ electrons. Suppression of ${T}_{c}$ in mixed valence superconductors is much weaker. Our theory has the most validity in the low-temperature Fermi liquid regime, without reentrant behavior of ${T}_{c}$. To check its applicability, we performed the fit for the $x$ dependence of ${T}_{c}$ in ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Ru}}_{3}{\mathrm{Si}}_{2}$ and obtained an excellent agreement with the experimental data, although no reentrance was found in this case. Other experimental data are discussed in the light of our theoretical analysis. In particular, we compare temperatures of the superconducting transition for some known homologs, i.e., the analog periodic lattice compounds with and without $f$ elements. For a few pairs of homologs, superconductivity exists only in the heavy fermion materials, thus confirming the uniqueness of superconductivity mechanisms for the latter. We suggest that for some other compounds, the value of ${T}_{c}$ may remain of the same order in the two homologs, if superconductivity originates mainly on some light Fermi surface, but induces a sizable superconducting gap on another Fermi surface, for which hybridization or other heavy fermion effects are more significant. By passing, we cite the old results that show that the jump in the specific heat at the transition reflects the heaviness of carriers on this Fermi surface independently of mechanisms responsible for superconductivity.