Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2 (original) (raw)
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Fermiology of cuprates from first principles: From small pockets to the Luttinger Fermi surface
Physical Review B, 2008
Fermiology, the shape and size of the Fermi surface, underpins the low-temperature physical properties of a metal. Recent investigations of the Fermi surface of high-T c superconductors, however, show a most unusual behavior: upon addition of carriers, "Fermi" pockets appear around nodal (hole doping) and antinodal (electron doping) regions of the Brillouin zone in the "pseudogap" state. With progressive doping, δ, these evolve into well-defined Fermi surfaces around optimal doping (δ opt ), with no pseudogap. Correspondingly, various physical responses, including d-wave superconductivity, evolve from highly anomalous, up to δ opt , to more conventional beyond. Describing this evolution holds the key to understanding high-temperature superconductivity. Here, we present ab initio quantum chemical results for cuprates, providing a quantitative description of the evolution of the Fermi surface with δ. Our results constitute an ab initio justification for several, hitherto proposed semiphenomenological theories, offering an unified basis for understanding of various, unusual physical responses of doped cuprates.
Heavy Electrons at Metallic Fermi Surfaces, a Superlattice Property
Physical Review Letters, 1996
The near-E F electronic structure and Fermi surface of Cu͞Co superlattices are investigated by a tightbinding model and the Green function matching method. The more striking feature is the development of extremely dispersionless bands. Variation of the Cu and Co slab thicknesses changes the superlattice bands' energy. For periodic values of the Co thickness, Cu͞Co superlattices exhibit a one-particle flat band at the Fermi level. As a consequence, a significant region of the superlattice Fermi surface has three-dimensional character. [S0031-9007(96)00490-5]
Theory of superconductivity in hole-doped monolayer MoS2
Physical Review B
We theoretically investigate the Cooper-pair symmetry to be realized in hole-doped monolayer MoS2 by solving linearized BCS gap equations on the three-orbital attractive Hubbard-like model in the presence of the atomic spin-orbit coupling. In hole-doped monolayer MoS2, both spin-orbit coupling and the multi-orbital effects are more prominent than those of electron-doped system. Near the valence band edge, the Fermi surfaces are composed of three different types of hole pockets, namely, one mainly consisting of the almost spin-degenerate |d z 2 orbital near Γ point, and the others of the spin-split upper and lower bands near K and K ′ points arising from the |d x 2 −y 2 and |dxy orbitals. The number of relevant Fermi pockets increases with increase of the doping. At very low doping, the upper split bands of |d x 2 −y 2 and |dxy are concerned, yielding extremely low Tc due to small density of states of the split bands. For further doping, the conventional spin-singlet state (SS) appears in the Γ pocket, which has a mixture of the spin-triplet (orbital-singlet) (ST-OS) and spinsinglet (orbital-triplet) (SS-OT) states in the K and K ′ pockets. The ratio of the mixture depends on the relative strength of the interactions, and the sign of the exchange interactions. Moderately strong ferromagnetic exchange interactions even lead to the pairing state with the dominant ST-OS state over the conventional SS one. With these observations, we expect that the fascinating pairing with relatively high Tc emerges at high doping that involves all the three Fermi pockets.
Fermi surface nesting in several transition metal dichalcogenides
New Journal of Physics, 2008
By means of high-resolution angle resolved photoelectron spectroscopy (ARPES) we have studied the fermiology of 2H transition metal dichalcogenide polytypes TaSe 2 , NbSe 2 , and Cu 0.2 NbS 2 . The tightbinding model of the electronic structure, extracted from ARPES spectra for all three compounds, was used to calculate the Lindhard function (bare spin susceptibility), which reflects the propensity to charge density wave (CDW) instabilities observed in TaSe 2 and NbSe 2 . We show that though the Fermi surfaces of all three compounds possess an incommensurate nesting vector in the close vicinity of the CDW wave vector, the nesting and ordering wave vectors do not exactly coincide, and there is no direct relationship between the magnitude of the susceptibility at the nesting vector and the CDW transition temperature. The nesting vector persists across the incommensurate CDW transition in TaSe 2 as a function of temperature despite the observable variations of the Fermi surface geometry in this temperature range. In Cu 0.2 NbS 2 the nesting vector is present despite different doping level, which lets us expect a possible enhancement of the CDW instability with Cu-intercalation in the Cu x NbS 2 family of materials. PACS numbers: 71.45.Lr 79.60.-i 71.18.+y 74.25.Jb
Dynamical breakup of the Fermi surface in a doped mott insulator
Physical review letters, 2005
The evolution from an anomalous metallic phase to a Mott insulator within the two-dimensional Hubbard model is investigated by means of the Cellular Dynamical Mean-Field Theory. We show that the density-driven Mott metal-insulator transition is approached in a non-uniform way in different regions of the momentum space. This gives rise to a breakup of the Fermi surface and to the formation of hot and cold regions, whose position depends on the hole or electron like nature of the carriers in the system. PACS numbers: 71.10.Fd, 71.27.+a, 74.20.Mn, The mechanism of high-temperature superconductivity remains mysterious after nearly two decades of research. Among many theoretical proposals, a line of thought stresses the importance of the proximity to a Mott insulating state and of understanding the anomalous metallic state originating from doping this Mott insulator, a state which is not described by Fermi-liquid theory . Along this path two very different approaches have been implemented: variational wavefunction studies [2] and slave boson approaches . These methods allow to connect the Mott insulator to an anomalous normal state, interpreting the phenomenon of high temperature superconductivity as a direct consequence of the proximity to the Mott Metal-Insulator Transition (MIT). Their early successes include the prediction of the d-wave symmetry of the order parameter, the existence of a pseudogap close to half-filling and the dome-like shape of the critical temperature.
Nature Physics
The strange-metal state is a crucial problem in condensed matter physics highlighted by its ubiquity in almost all major correlated systems 1-7. Its understanding could provide important insight into high-Tc superconductivity 2 and quantum criticality 8. However, with the Fermi liquid theory failing in strange metals, understanding the highly unconventional behaviors has been a long-standing challenge. Fundamental aspects of strange metals remain elusive, including the nature of their charge carriers 1. Here, we report the observation of a giant Nernst response in the strange-metal state in a two-dimensional superconductor 2M-WS2. A giant Nernst coefficient comparable to the vortex Nernst signal in superconducting
Local Density of States induced near Impurities in Mott Insulators
arXiv: Strongly Correlated Electrons, 2018
The local density of states near dopants or impurities has recently been probed by scanning tunneling microscopy in both the parent and very lightly doped compounds of the high-$T_c$ cuprate superconductors. Our calculations based on a slave-rotor description account for all the following key features of the observed local density of states: i) positions and amplitudes of the in-gap spectral weights of a single impurity; ii) the spectral weight transfer from the upper Hubbard band to the lower Hubbard band; iii) the difference between the cases of single and multiple impurities. For multiple impurities, our study explains the complete suppression of spectral weight observed at precisely the Fermi energy and links this property to zeros of the underlying bulk Green's function of the Mott insulating phase.
Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor
Scientific Reports, 2015
In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature T c ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other ironbased compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe 0.92 Co 0.08 AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.