Angle-Resolved Photoemission Spectroscopy of the Antiferromagnetic SuperconductorNd1.87Ce0.13C

Abstract

We performed high-resolution angle-resolved photoemission spectroscopy on Nd1.87Ce0.13CuO4, which is located at the boundary of the antiferromagnetic (AF) and the superconducting phase. We observed that the quasiparticle (QP) effective mass around (π, 0) is strongly enhanced due to the opening of the AF gap. The QP mass and the AF gap are found to be anisotropic, with the largest value near the intersecting point of the Fermi surface and the AF zone boundary. In addition, we observed that the QP peak disappears around the Néel temperature (TN ) while the AF pseudogap is gradually filled up at much higher temperatures, possibly due to the short-range AF correlation.Since the discovery of cuprate high-temperature superconductors (HTSCs), intensive experimental and theoretical studies have been performed to elucidate the origin and mechanism of the anomalously high superconducting (SC) transition temperature. It is now widely accepted that electrons or holes doped into the parent Mott insulator interact antiferromagnetically with each other on the quasi-two dimensional CuO 2 plane. Although it has been suggested that the antiferromagnetic (AF) interaction plays an essential role for pairing of electrons (holes) in the SC state, it is still unclear how the antiferromagnetism interplays with the superconductivity at the microscopic level. This problem is a central issue not only in HTSCs but also in other exotic superconductors such as heavy-fermion and organic-salt superconductors. In the phase diagram of electron-doped cuprates, the AF and SC phases are adjacent to each other or somewhat overlap at the boundary, in contrast to the hole-doped case where the two phases are well separated [1]. The proximity or overlapping between the AF and SC phases in the electron-doped cuprates yields a good opportunity for studying the interplay between the AF interaction and the superconductivity [2,3,4,5]. In fact, a recent elastic neutron-scattering experiment reported a competitive nature between the AF long-range order and the superconductivity [2]. On the other hand, an inelastic neutron scattering experiment observed coexistence of the gapped commensurate spin fluctuation and the superconductivity [3]. In contrast to these intensive studies on the "qresolved" spin dynamics by neutron scattering, a limited number of photoemission studies on the "k-resolved" electronic structure have been reported for electron-doped cuprates [6,7]. The k-dependence of the AF correlation effect on the electronic structure is essential to understand the interplay between the antiferromagnetism and the superconductivity.In this Letter, we report high-resolution angle-resolved photoemission spectroscopy (ARPES) on electron-doped cuprate Nd 1.87 Ce 0.13 CuO 4 (NCCO, x = 0.13) located at the phase boundary between the AF and SC phases. We found the mass-renormalized quasiparticle (QP) state near (π, 0), which gradually evolves into the high-energy gap [6] around the hot spot. The observed continuous evolution of the electronic structure near the Fe...

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

“…Therefore, the nodal 'kink' observed here for high-energy excitations is neither due to any possible extrinsic effect nor due to matrix element effects, but due to an intrinsic effect, being a characteristic of bulk Nd 1.85 Ce 0.15 CuO 4 . The presence (absence) of the nodal (antinodal) 'kink' in QD observed by the present high-hν ARPES is much different from the results of low-hν ARPES so far reported for NCCO [5,6].…”

“…No clear 'kink' is observed in our high-hν ARPES for Nd 1.85 Ce 0.15 CuO 4 along the antinodal direction as shown in figures 2(a) and (b), although an antinodal 'kink' was suggested by the low-hν ARPES for NCCO [5]. 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. Such an enhancement of the quasiparticle effective mass near E F is gradually suppressed due to their movement away from the 'hot spot' toward (π , 0) [6]. Neither the antiferromagnetic 'pseudo-gap' behavior nor the near-E F quasiparticle mass enhancement are clearly seen along the antinodal direction by our high-hν ARPES in figures 2(a) and (b), which implies that both effects are weak in the bulk.…”

“…For quasi-two-dimensional electron systems such as HTSCs, it has long been thought that the electronic structures of the top (or surface) conducting layer are equivalent to those of the bulk layers, which are responsible for the superconductivity. High-hν core-level PES studies [21]- [26], however, recently suggested that the electronic structures of the bulk CuO 2 layers, in particular for optimally doped Nd 1.85 Ce 0.15 CuO 4 , are noticeably different from those of the surface CuO 2 layer, which are mainly detected by low-hν ARPES [6,8,22]. High-hν ARPES [23,24] is therefore essential for directly revealing the bulk QD.…”

Hall Resistivity Correlations in Disordered Electron-Doped $$\hbox {Nd}_{2-x}\hbox {Ce}_x\hbox {CuO}_{4+\delta }$$ Nd 2 - x

“…An important topic of discussion of the features in electron-doped compounds is a competition of d-wave SC and AF order and the presence or absence of spin-or charge-density wave phases in underdoped region [10,11]. Exactly in this range in n-doped cuprates a Fermi surface change from electron-like pockets to a coexisting of a small hole-like and electron-like pockets is observed [3,12,13]. All of these facts motivate us to investigate the dependencies of the electrical ρ xx (B) and Hall ρ xy (B) resistivity in external magnetic field in electron-doped Nd 2−x Ce x CuO 4+δ with nonstochiometric disorder (δ) in order to analyze the conditions for the appearance of the Hall and dissipative resistivity correlations in the presence of evolution from AF -(underdoped region) to SC -order (optimally doped region).…”