Electronic Structure Correspondence of Singlet-Triplet Scale Separation in Strained Sr2RuO4
Electronic Structure Correspondence of Singlet-Triplet Scale Separation in Strained Sr2RuO4
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DOI：
10.3390/app11020508
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发表时间：
2020-11
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影响因子：
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通讯作者：
Swagata Acharya;D. Pashov;Elena Chachkarova;M. Schilfgaarde;C. Weber
中科院分区：
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作者：
Swagata Acharya;D. Pashov;Elena Chachkarova;M. Schilfgaarde;C. Weber
在大约1 K的温度下，Sr 2 RuO 4经历从正常费米液体到超导相的转变。尽管前者相对简单且易于理解，但超导态经过25年的研究仍然没有被理解。最近，已经发现，临界温度可以通过施加单轴应变而提高，直到临界应变，在该临界应变之后，临界温度福尔斯下降。在这项工作中，我们采取了“不稳定”的方法，并寻求分歧的敏感性。这提供了一种无偏的方式来区分竞争基态的倾向。我们表明，在无应变的化合物，单重态和三重态的正常费米液相的不稳定性是紧密间隔。在单轴应变下，所有对费米学有贡献的轨道上的电子变得更相干，而Ru-dxy特征的电子变得更重，Ru-dxz，yz特征的电子变得更轻。在此过程中，Im χ（q，ω）在q =（0.3，0.3，0）2π/a和q =（0.5，0.25，0）2π/a附近迅速增加，而在所有其他公度矢量处，特别是在q = 0处，Im χ（q，ω）被抑制，这对自旋三重态超导性至关重要。我们观察到应变下的磁各向异性平稳下降，这是伴随着单重态不稳定性的增加。因此，三重态超导不稳定性仍然是系统的滞后不稳定性，而单重态不稳定性在应变下增强，导致这些竞争不稳定性之间的大能量尺度分离。然而，由于这种情况甚至在没有自旋轨道耦合的情况下也会发生，因此我们认为主要是准反铁磁矢量周围的自旋涨落胶的增强驱动了库珀配对，而不是磁各向异性。在大应变下，自旋密度波的不稳定性超过超导的不稳定性。分析依赖于一个高保真度，从头计算描述的单粒子的属性和两个粒子的亲合性，基于准粒子自洽GW近似增强动力学平均场理论。这种方法被描述和它的高保真度通过比较所观察到的一个和两个粒子的属性确认。
At a temperature of roughly 1 K, Sr2RuO4 undergoes a transition from a normal Fermi liquid to a superconducting phase. Even while the former is relatively simple and well understood, the superconducting state has not even been understood after 25 years of study. More recently, it has been found that critical temperatures can be enhanced by the application of uniaxial strain, up to a critical strain, after which it falls off. In this work, we take an “instability” approach and seek divergences in susceptibilities. This provides an unbiased way to distinguish tendencies to competing ground states. We show that in the unstrained compound, the singlet and triplet instabilities of the normal Fermi liquid phase are closely spaced. Under uniaxial strain, electrons residing on all orbitals contributing to the Fermiology become more coherent, while the electrons of the Ru-dxy character become heavier, and the electrons of the Ru-dxz,yz characters become lighter. In the process, Im χ(q,ω) increases rapidly around q = (0.3,0.3,0)2π/a and q = (0.5,0.25,0)2π/a, while it gets suppressed at all other commensurate vectors, in particular at q = 0, which is essential for spin-triplet superconductivity. We observe that the magnetic anisotropy under strain drops smoothly, which is concomitant with the increment in singlet instability. Thus, the triplet superconducting instability remains the lagging instability of the system, and the singlet instability enhances under strain, leading to a large energy-scale separation between these competing instabilities. However, since this happens even without spin-orbit coupling, we believe it is primarily the enhancement in the spin fluctuation glue around quasi-anti-ferromagnetic vectors that drives the Cooper pairing instead of the magnetic anisotropy. At large strain, an instability to a spin density wave overtakes the superconducting one. The analysis relies on a high-fidelity, ab initio description of the one-particle properties and two-particle susceptibilities, based on the quasiparticle self-consistent GW approximation augmented by dynamical mean field theory. This approach is described and its high fidelity confirmed by comparing to observed one- and two-particle properties.