Electronic structure of electron-dopedSm1.86Ce0.14CuO4: Strong pseudogap effects, nodeless gap, and signatures of short-range order

Abstract

Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm1.86Ce0.14CuO4 shows a much stronger pseudo-gap or "hot-spot" effect than that observed in other optimally doped n-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that d-wave superconductivity in this compound would be of a novel "nodeless" gap variety. The gross features of the Fermi surface topology and low energy electronic structure are found to be well described by reconstruction of bands by a √ 2× √ 2 order. Comparison of the ARPES and optical data from the same sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap effects. However, the high energy electronic structure is found to be inconsistent with such a scenario. We show that a number of these model inconsistencies can be resolved by considering a short range ordering or inhomogeneous state.PACS numbers: 74.25. Jb, In spite of their many interesting physical properties 1,2,3,4 , electron-doped HTSCs have been much less studied as compared to the hole-doped HTSCs. It was not until a few years ago that high resolution ARPES was applied and there are still only a handful of published papers on the subject. In their high resolution ARPES studies, Armitage et al. found that for the highest T c samples of Nd 1.85 Ce 0.15 CuO 4 (NCCO) the near E F spectral weight was strongly suppressed at the momentum space positions where the underlying Fermi surface (FS) contour crosses the AF Brillouin zone boundary (AFZB) suggesting the existence of a (π,π) scattering channel 5 . It was also found that for (x=0.04) underdoped samples an electron FS pocket exists around (π,0) point and that at higher dopings spectral weight increases near (π/2,π/2) which eventually completes the large hole-like FS pocket around the (π,π) point 6 . A possible way to view the results for the highest-T c samples -at least qualitatively -is as a manifestation of a band reconstruction from a √ 2 × √ 2 static (or slowly fluctuating) spin density wave (SDW) or similar symmetry order 7 . Such a picture explains hot spots on the FS contour as due not to the opening of a 'pseudo-gap' per se but instead due to a band folding and then splitting across the AFZB giving FS pockets around (π/2, π/2) and (π, 0). Such a simple two band interpretation enables one to understand issues such as the sign change in the Hall coefficient 8 and optical conductivity 9 spectra. However, systematic studies to test the model are lacking and there may be doubts that such a simple picture could describe the data at the level of small details.Motivated by these issues, we have performed an extensive high resolution ARPES study on another compound in the small family of electron-doped HTSCs Sm 1.85 Ce 0.15 CuO 4 (SCCO) as well as optical reflection measurements. A quantitative analysis yields a number of important observat...

Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by protect annealing

“…Angle-resolved photoemission spectroscopy (ARPES) studies have shown that the pseudogap opens around the hot spots, namely, crossing points of the Fermi surface (FS) with the AFM Brillouin zone boundary in superconducting samples456. A neutron scattering study7 has revealed that the AFM correlation length is of order ∼10 lattice spacing in the superconducting phase, and the pseudogap in the ARPES spectra of the superconducting phase has been reproduced by assuming a similar AFM correlation length89.…”

Annealing condition dependence of the superconducting property and the pseudo-gap in the protect-annealed electron-doped cuprates

“…The EDC of PLCCO#1 for the nodal point, however, shows that the leading edge is shifted from the Fermi energy. This may be induced by the strong AFM as the Fermi momentum along nodal is very close to the AFM Brillouin-zone boundary [10]. One more thing about which we need to discuss is the line-shape of the EDCs at the nodal point.…”

Bulk electronic structures and strong electron–phonon interactions in an electron-doped high-temperature superconductor

“…It has recently been suggested that the antinodal 'kink' behavior is related to the antiferromagnetic 'pseudo-gap' at the 'hot spots' for NCCO [6]. Stronger antiferromagnetic 'pseudo-gap' and 'hot spot' effects are reported in the other electron-doped HTSC, Sm 1.86 Ce 0.14 CuO 4 [9]. It is found that the quasiparticle effective mass near the Fermi level (E F ) is most strongly enhanced in the close vicinity of the 'hot spot' due to the opening of the antiferromagnetic 'pseudo-gap' for those electron-doped HTSCs.…”

“…For the hole-doped HTSCs, the 'kink' behavior along the nodal [(0, 0)-(π, π )] direction is interpreted as indicating strong coupling with longitudinal optical phonons, because it is observed even for La 2−x Sr x CuO 4 where the magnetic mode does not exist [2]- [4]. For the electron-doped HTSCs, on the other hand, no 'kink' behavior is observed along the nodal direction while the finite 'kink' or the antiferromagnetic 'pseudo-gap' behavior is seen along the antinodal [(π , 0)-(π, π)] and off-nodal directions by low-hν ARPES [5]- [9]. For both the hole-and electron-doped HTSCs, it is considered that the 'kink' behavior along the antinodal and off-nodal directions is depicted by the magnetic excitation mode because the electrons near (π, 0) are easily coupled to the magnetic mode with a Q vector of (π, π ) [7,10,11].…”