Abstract
The iso-electronic series, Ca2−xSrxRuO4, is studied within the GGA (and spin-orbit coupled GGA) plus DMFT formalism using the hybridization expansion of continuous time Quantum Monte Carlo (CT-QMC) impurity solver. GGA+DMFT, along with CT-QMC impurity solver we used, provides insights into the retarded electronic correlations at finite temperatures. We use GGA+U and energy considerations at T = 0 for complementary understanding of the ground state structural and electronic properties. While the dynamical correlations make Sr2RuO4 a Hund’s metal, they drive Ca2RuO4 to a Mott insulating ground state. We study the single-particle and two-particle responses at three different points (x = 2.0, 0.5, 0.0) to understand the anomalous cross-over from Hund’s metal (x = 2.0 ) to a Mott insulator (x = 0) and observe that a structural distortion is likely to be responsible. Further, dynamical correlations reveal that the band-width (W) of the Hund’s metal is larger than its effective local Hubbard U, and a finite Hund’s coupling JH helps it remain in a bad metallic and nearly spin-frozen state over a large temperature range. Ca2RuO4, though, is driven to the proximity of a Mott transition by the narrowing of band width (U/W > 1.5). We show that there is a critical end point of second-order structural transition at x = 0.5, where spin fluctuations become critical and follow the scaling of local quantum criticality. We argue that this critical end point of quasi-3D nature is associated with an effective dimensional cross-over from the quasi-2D structures of x = 2.0 and x = 0.0 end-members. Finally we draw an electronic and magnetic phase diagram in T-x plane with these novel inputs, with a fan like region starting from the quantum critical end point at x = 0.5.
Highlights
Introduction ce pte cri ptPartially filled d- and f-electron systems are usually correlated electronic materials and the proximity of a Mott transition makes some of these materials rather interesting [1; 2].Mott metal-insulator (MIT) transition, heavy fermion behaviour, unconventional highTc superconductivity, colossal magnetoresistance are some of the dramatic phenomena arising, solely or partly, due to strong local correlations
This, in turn, gives us the Wannier orbitals around the Fermi level which serve as inputs to the DMFT selfconsistency calculation
We discuss below the results we obtained from DFT+DMFT calculations on Sr2 RuO4 without and with SO coupling
Summary
Mott metal-insulator (MIT) transition, heavy fermion behaviour, unconventional highTc superconductivity, colossal magnetoresistance are some of the dramatic phenomena arising, solely or partly, due to strong local correlations. They can fall in either of the effective single or multi-orbital (MO) framework depending on the active orbitals at the Fermi level. The Hund’s coupling leads to an exponential suppression of the coherence scale of a MO metal and leads to a large spin-frozen non Fermi-liquid phase. Hund’s coupling has profound and distinct effects on spin, orbital and charge degrees of freedom
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