Strong Correlations from Hund’s Coupling

Georges, Antoine; Medici, Luca de’; Mravlje, Jernej

doi:10.1146/annurev-conmatphys-020911-125045

Cited by 797 publications

(932 citation statements)

References 243 publications

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“…The robustness of the electronic structure is consistent with transport measurements: upon increasing temperature the resistivity smoothly decreases and the insulating behavior persists at least up to 300 K; no abnormal behavior is observed in the vicinity of T N ; see Fig 1 b). While not excluding other more sophisticated models (e.g., orbital-selective Mott physics [9,10,34]) that would be able to quantitatively account for the experimental results on this material, the basic picture described here provides a qualitatively consistent explanation for the experimental results from neutron scattering, transport and ARPES measurements. This picture in which Mott physics plays a key role for the insulating behavior in highly Cu-doped NaFe 1-x Cu x As is strongly supported by a recent STM study on insulating NaFe 0.7 Cu 0.3 As which reports striking similarities to lightly doped cuprates [24].…”

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confidence: 66%

NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction

Matt

et al. 2016

Phys. Rev. Lett.

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In the studies of iron-pnictides, a key question is whether their bad-metal state from which the superconductivity emerges lies in close proximity with a magnetically ordered insulating phase. Recently it was found that at low temperatures, the heavily Cu-doped NaFe1-xCuxAs (x > 0.3) iron-pnictide is an insulator with long-range antiferromagnetic order, similar to the parent compound of cuprates but distinct from all other iron-pnictides. Using angle-resolved photoemission spectroscopy, we determined the momentum-resolved electronic structure of NaFe1-xCuxAs (x = 0.44) and identified that its ground state is a narrow-gap insulator. Combining the experimental results with density functional theory (DFT) and DFT+U calculations, our analysis reveals that the on-site Coulombic (Hubbard) and Hund's coupling energies play crucial roles in formation of the band gap about the chemical potential. We propose that at finite temperatures charge carriers are thermally excited from the Cu-As-like valence band into the conduction band, which is of Fe 3d-like character. With increasing temperature, the number of electrons in the conduction band becomes larger and the hopping energy between Fe sites increases, and finally the long-range antiferromagnetic order is destroyed at T > TN. Our study provides a basis for investigating the evolution of the electronic structure of a Mott insulator transforming into a bad metallic phase, and eventually forming a superconducting state in iron-pnictides.

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confidence: 66%

NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction

Matt

et al. 2016

Phys. Rev. Lett.

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“…It is important to note that the Hund coupling J is crucial to reach the insulating phase, and increasing J lowers the critical value U c2 substantially. 61 In order to check if our computational parameters in the two-band case allow for the occurence of the sharp features in the Hubbard satellites, we first performed a test using U /D = 0, J/D = 0, in which case the two band problem decouples into two independent SIAMs. Indeed, using a value of U close enough to the transition we can still resolve the sharp features (not shown), meaning that the accuracy of the method is high enough also for the two band case.…”

Section: Two-band Hubbard Modelmentioning

confidence: 99%

Efficient DMFT impurity solver using real-time dynamics with matrix product states

et al. 2015

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We propose to calculate spectral functions of quantum impurity models using the Time Evolving Block Decimation (TEBD) for Matrix Product States. The resolution of the spectral function is improved by a so-called linear prediction approach. We apply the method as an impurity solver within the Dynamical Mean Field Theory (DMFT) for the single-and two-band Hubbard model on the Bethe lattice. For the single-band model we observe sharp features at the inner edges of the Hubbard bands. A finite size scaling shows that they remain present in the thermodynamic limit. We analyze the real time-dependence of the double occupation after adding a single electron and observe oscillations at the same energy as the sharp feature in the Hubbard band, indicating a long-lived coherent superposition of states that correspond to the Kondo peak and the side peaks. For a two-band Hubbard model we observe an even richer structure in the Hubbard bands, which cannot be related to a multiplet structure of the impurity, in addition to sharp excitations at the band edges of a type similar to the single-band case.

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“…The specific role of the Fe 3d levels for the electronic correlations in Fe-based superconductors reflects the Coulomb (Hubbard and Hund) interactions as well as the small crystal-electric-field splittings [25][26][27]. To better understand the observed mass enhancement, we study the electron correlation effects in a multiorbital Hubbard model for A122 using a U (1) slave-spin meanfield theory [28].…”

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confidence: 99%

Strain-Driven Approach to Quantum Criticality inAFe2As2withA

et al. 2016

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Superconductors close to quantum phase transitions often exhibit a simultaneous increase of electronic correlations and superconducting transition temperatures. Typical examples are given by the recently discovered iron-based superconductors. We investigated the band-specific quasiparticle masses of AFe2As2 single crystals with A = K, Rb, and Cs and determined their pressure dependence. The evolution of electronic correlations could be tracked as a function of volume and hole doping. The results indicate that with increasing alkali-metal ion radius a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to suppress the superconductivity.PACS numbers: 74.70. Xa,71.18.+y,74.40.Kb,71.27.+a Unconventional superconductivity (SC) often emerges in the proximity of continuous, zero-temperature phase transitions, so-called quantum critical points (QCPs). In particular, the onset of magnetic order is generally believed to drive SC by magnetic quantum criticality. Examples encompass the cuprates, organic metals, heavyfermion systems, and the recently discovered iron-based superconductors. A particularly illustrative example is given by BaFe 2 (As 1−x P x ) 2 . Here, the application of chemical pressure, by replacing As with isovalent, smaller P ions, suppresses antiferromagnetic (AF) order resulting in an extended superconducting dome with a maximum transition temperature T c ≈ 30 K at the critical concentration x c = 0.3 [1]. The QCP at x c shielded by SC was anticipated theoretically [2] and observed through strongly enhanced quasiparticle masses and deviations from Fermi-liquid (FL) behavior. In this Letter we show that the isostructural superconductor KFe 2 As 2 can likewise be pushed towards a QCP by substituting isovalent Rb and Cs for K. In these compounds, in contrast to the examples listed above and despite general consensus, the proximity to a QCP appears to suppress SC.The alkali metal series AFe 2 As 2 (A122) with A = K, Rb, and Cs represents one of the rare examples of stoichiometric iron-arsenide superconductors. According to LDA calculations their low T c values of less than 3.5 K cannot be explained by electron-phonon coupling. Angleresolved photoemission spectroscopy and thermal conductivity measurements suggest an unconventional pairing mechanism [3][4][5][6]. Recent specific-heat measurements reveal huge Sommerfeld coefficients γ which exceed those of BaFe 2 (As 1−x P x ) 2 in apparent contradiction to the low

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Strong Correlations from Hund’s Coupling

Cited by 797 publications

References 243 publications

NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction

NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction

Efficient DMFT impurity solver using real-time dynamics with matrix product states

Strain-Driven Approach to Quantum Criticality inAFe2As2withA

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