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Register a new userElectronic Structure and Correlation Effects in PuCoIn5 as compared to PuCoGa5
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Since their discovery nearly a decade ago, plutonium-based superconductors have attracted considerable interest, which is now heightened by the latest discovery of superconductivity in PuCoIn5. In the framework of density functional theory (DFT) within the generalized gradient approximation (GGA) together with dynamical mean-field theory (DMFT), we present a comparative study of the electronic structure of PuCoIn5 with the related material, PuCoGa5. Overall, a similar GGA-based electronic structure, including the density of states, energy dispersion, and Fermi surface topology, was found for both compounds. The GGA Pu 5f band was narrower in PuCoIn5 than in PuCoGa5, resulting in an effective reduction of Kondo screening in the former system, as also shown by DMFT calculations. This phenomenon is due to the expanded lattice for PuCoIn5.
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In this work we present a comparative investigation of the electronic structures of NbO$_2$ and VO$_2$ obtained within the combination of density functional theory and cluster-dynamical mean field theory calculations. We investigate the role of dynamic electronic correlations on the electronic structure of the metallic and insulating phases of NbO$_2$ and VO$_2$, with focus on the mechanism responsible for the gap opening in the insulating phases. For the rutile metallic phases of both oxides, we obtain that electronic correlations lead to strong renormalization of the $t_{2g}$ subbands, as well as the emergence of incoherent Hubbard subbands, signaling that electronic correlations are also important in the metallic phase of NbO$_2$. Interestingly, we find that nonlocal dynamic correlations do play a role in the gap formation of the (bct) insulating phase of NbO$_2$, by a similar physical mechanism as that recently proposed by us in the case of the (M$_1$) dimerized phase of VO$_2$ (textit{Phys. Rev. Lett. 117, 056402 (2016)}). Although the effect of nonlocal dynamic correlations in the gap opening of bct phase is less important than in the (M$_1$ and M$_2$) monoclinic phases of VO$_2$, their presence indicates that the former is not a purely Peierls-type insulator, as it was recently proposed.
We show, by means of ab-initio calculations, that electron-electron correlations play an important role in potassium-doped picene ($K_x$-picene), recently characterized as a superconductor with $T_c = 18K$. The inclusion of exchange interactions by means of hybrid functionals reproduces the correct gap for the undoped compound and predicts an antiferromagnetic state for $x=3$, where superconductivity has been observed. The latter finding is compatible with a sizable value of the correlation strength, in agreement with simple estimates. Our results highlight the similarity between potassium-doped picene and alkali-doped fulleride superconductors.
The BaNi$_2$As$_2$ compound is investigated using both the angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and combined computational scheme of local density approximation together with dynamical mean-field theory (LDA+DMFT). For more realistic comparison of LDA+DMFT spectral functions with ARPES data we take into account several experimental features: the photoemission cross-section, the experimental energy and angular resolutions and the photo-hole lifetime effects. In contrast to isostructural iron arsenides the BaNi$_2$As$_2$ within LDA+DMFT appears to be weakly correlated (effective mass enhancement about $1.2$). This dramatic reduction of the correlation strength comes from the increase of 3d-orbital filling, when going from Fe to Ni, together with rather large bare Ni-3d LDA bandwidth. Nevertheless, even weakened electron correlations cause remarkable reconstruction of the bare BaNi$_2$As$_2$ LDA band structure and corresponding LDA+DMFT calculations provide better agreement with ARPES than just renormalized LDA results.
FeSe is classed as a Hunds metal, with a multiplicity of $d$ bands near the Fermi level. Correlations in Hunds metals mostly originate from the exchange parameter emph{J}, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with $d_{xy}$ the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hunds systems. By applying a recently developed high-fidelity emph{ab initio} theory, we show explicitly the connections between correlations in $d_{xy}$ and the superconducting critical temperature $T_{c}$. Starting from the emph{ab initio} results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls $T_{c}$. We show small excursions in $J$ can cause colossal changes in $T_{c}$. Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO$_{3}$ substrate (M-FeSe/STO). The twin conditions of proximity of the $d_{xy}$ state to the Fermi energy, and the strength of $J$ emerge as the primary criteria for incoherent spectral response and enhanced single- and two-particle scattering that in turn controls $T_{c}$. Using constrained RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance $J$. We explain why M-FeSe/STO has a high $T_{c}$, whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls $T_{c}$ in bulk, layers, and interfaces of Hunds metals by hole pocket and electron screening cloud engineering.
We study the optical properties of the layered rhodium oxide K0.49RhO2, which is isostructural to the thermoelectric material NaxCoO2. The optical conductivity shows broad interband transition peaks as well as a low-energy Drude-like upturn, reminiscent of the optical spectra of NaxCoO2. We find that the peaks clearly shift to higher energies with respect to those of NaxCoO2, indicating a larger crystal-field splitting between eg and t2g bands in K0.49RhO2. The Drude weights suggest that the effective mass of K0.49RhO2 is almost two times smaller than that of NaxCoO2. These differences in electronic structures and correlation effects between NaxCoO2 and K0.49RhO2 are discussed in terms of the difference between Co 3d and Rh 4d orbitals.
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