Transport Properties of Metallic Ruthenates: ADFT+DMFTInvestigation

Abstract

We present a systematical theoretical study on the transport properties of an archetypal family of Hund's metals, Sr2RuO4, Sr3Ru2O7, SrRuO3 and CaRuO3, within the combination of first principles density functional theory and dynamical mean field theory. The agreement between theory and experiments for optical conductivity and resistivity is good, which indicates that electron-electron scattering dominates the transport of ruthenates. We demonstrate that in the single-site dynamical mean field approach the transport properties of Hund's metals fall into the scenario of "resilient quasiparticles". We explains why the single layered compound Sr2RuO4 has a relative weak correlation with respect to its siblings, which corroborates its good metallicity. PACS numbers: 71.27.+a, The anomalous transport properties in correlated metals have been of great interest for many decades, but the main focus was the electron-electron scattering due to Hubbard-like short range repulsion. Many features found in realistic materials are well captured by the dynamical mean field theory (DMFT) in simple Hubbard models [1,2], for example, the very low coherence scale T F L below which Fermi liquid (FL) theory holds [3], and the high temperature "bad metal" behavior that resistivity exceeds the Mott-Ioffe-Regel limit [4]. In the broad crossover regime between FL and "bad metal" the "resilient quasiparticles" which survive up to high temperature [5,6] dominate the transport. Very recently Hund's metals [7] have attracted a lot of attentions. These are materials in which the Hund's interaction rather than the Hubbard repulsion gives rise to the heavy quasiparticle mass in several transition metal compounds such as iron pnictides [8] and ruthenates [9,10]. The understanding of the scattering mechanism in Hund's metals and their consequences for the transport properties have not been explored much.In this paper we study the archetypal Hund's metals [9][10][11], the metallic members of Ruddlesden-Popper serials of ruthenates (A n+1 B n O 3n+1 ): Sr 2 RuO 4 (n = 1), Sr 3 Ru 2 O 7 (n = 2), SrRuO 3 and CaRuO 3 (n = ∞).Ruthenates have been extensively studied as prototypical strongly correlated systems, with large effective mass enhancements revealed by various experiments [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. They exhibit a very small coherence scale T F L , as well as a crossover into "bad metal" regime [25][26][27][28][29][30]. Surprisingly the single layered compounds Sr 2 RuO 4 is more metallic than the pseudocubic SrRuO 3 and CaRuO 3 at relative low temperature (≤ 400K). This is different from many other systems, for example, the Ruddlesden-Popper family of strontium vanadates, lanthanum nickelates, lanthanum cuprates, strontium iridates, where the single layered compounds are insulating and the pseudocubic ones are metallic.The method used in this paper is the combination of density functional theory and DMFT (DFT+DMFT) in the charge self-consistent and all electron formulation that avoids building the low energy Hubb...

Strongly Correlated Materials from a Numerical Renormalization Group Perspective: How the Fermi-Liquid State of Sr2RuO4 Emerges

“…With NRG as impurity solver, the entire DMFT calculation is performed on the real-frequency axis [35], and we can compute correlation functions at arbitrarily low energy scales and temperatures. Hence, we are able to go beyond previous Monte Carlo-based DFT+DMFT studies [24,26,27,33,[38][39][40][41] and enter deep into the Fermi-liquid regime, even down to T = 0 [42]. This enables us to explore the counter-intuitive observation that the more itinerant (xy) orbital has the smaller quasiparticle weight [21,24,27,38,41,44,45].…”

Quantum criticality associated with dimensional crossover in the iso-electronic series Ca2−x Sr x RuO4

“…The mass enhancement, related to the coefficient (s 1 ) of the linear term in the expansion * = + m m s 1 1 [43,44], increases with lowering of temperature (figure 2(c)). It can be seen that the xy orbital has a larger mass enhancement than the xz and yz orbitals [13,16], and concomitantly, the magnitude of the intercept of ImΣ(iω) at ω=0 for xy orbital is larger than that for the other two (figure 2(c)). The m * /m for d xy is 5.8 and for d xz , d yz 4.5, in excellent agreement with experiments and earlier theoretical studies.…”

“…The ground states and the finite temperature non-Fermi-liquid states are described within three-orbital DFT+DMFT framework with such values of U and J H . Large mass enhancement factors [16], substantial increment in the linear specific heat coefficient γ and absence of a Mott insulating phase are common to all these three materials. The difference between them, however, involves the nature of magnetic ground states and the Ru-O-Ru bond-angles.…”

“…The role of Van Hove singularity and J H have been extensively studied [19] in these compounds to rationalize their electronic and magnetic properties. Reasonable values of U and J have been gleaned [16,19,20] on these materials from experimental single and two-particle features. The ground states and the finite temperature non-Fermi-liquid states are described within three-orbital DFT+DMFT framework with such values of U and J H .…”

First-Principles Correlated Approach to the Normal State of Strontium Ruthenate

“…Very recent correlated first-principles calculations567 show that it is necessary to adequately include the complex interplay between one-electron band structure, local multi-band interactions and SOC to get a quantitative accord with dHvA data. Moreover, the IC-C crossover has been interpreted in terms of Hund’s metal physics8910, where sizable influence of Hund coupling ( J H ) drastically reduces the lattice-FL crossover scale. However, there is still no consensus on the details of the normal state (spin and charge) fluctuation spectra that can generate the specific pairing interaction needed to describe the SC pair symmetry constrained by multitude of data.…”