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Register a new userPhonon softening and anomalous mode near the $x_{c}=0.5$ quantum critical point in Ca$_{2-x}$Sr$_{x}$RuO$_4$
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Inelastic neutron scattering is used to measure the temperature dependent phonon dispersion in Ca$_{2-x}$Sr$_{x}$RuO$_{4}$ ($x=0.4$, 0.6). The in-plane $Sigma_{4}$ octahedral tilt mode softens significantly at the zone boundary of the high temperature tetragonal (HTT) textit{I4}$_{mathit{1}}$textit{/acd} structure as the temperature approaches the transition to a low temperature orthorhombic (LTO) textit{Pbca} phase. This behavior is similar to that in La$_2$CuO$_4$, but a new inelastic feature that is not found in the cuprate is present. An anomalous phonon mode is observed at energy transfers greater than the $Sigma_{4}$ albeit with similar dispersion. This anomalous phonon mode never softens below $sim 5$ meV, even for temperatures below the HTT-LTO transition. This mode is attributed to the presence of intrinsic structural disorder within the textit{I4}$_{mathit{1}}$textit{/acd} tetragonal structure of the doped ruthenate.
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The realistic description of correlated electron systems has taken an important step forward a few years ago as the combination of density functional methods and the dynamical mean-field theory was conceived. This framework allows access to both high and low energy physics and is capable of the description of the specific physics of strongly correlated materials, like the Mott metal-insulator transition. A very important step in the procedure is the interface between the band structure method and the dynamical mean-field theory and its impurity solver. We present a general interface between a projector augmented wave based density functional code and many-body methods based on Wannier functions obtained from a projection on local orbitals. The implementation is very flexible and allows for various applications. Quantities like the momentum resolved spectral function are accessible. We present applications to SrVO$_3$ and the metal-insulator transition in Ca$_{2-x}$Sr$_{x}$RuO$_4$.
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