Competition between Antiferromagnetism and Superconductivity in the Electron-Doped Cuprates Triggered by Oxygen Reduction

Abstract

We have performed a systematic angle-resolved photoemission study of as-grown and oxygenreduced Pr2−xCexCuO4 and Pr1−xLaCexCuO4 electron-doped cuprates. In contrast to the common belief, neither the band filling nor the band parameters are significantly affected by the oxygen reduction process. Instead, we show that the main electronic role of the reduction process is to remove an anisotropic leading edge gap around the Fermi surface. While the nodal leading edge gap is induced by long-range antiferomagnetic order, the origin of the antinodal one remains unclear.PACS numbers: 74.72. Jt, 74.25.Jb, 74.62.Dh, Even though most of the work has been focused on hole-doped cuprates, the understanding of their electrondoped counterparts is essential for obtaining a universal picture of high-Tc superconductivity. To achieve this goal, it is necessary to first solve the main mystery that holds since the discovery of the T'-structure electrondoped cuprates RE 2−x Ce x CuO 4 and RE 1−x LaCe x CuO 4 (RE = Pr, Nd, Sm, Eu): why is superconductivity in these compounds achieved only when a tiny amount of oxygen (∼ 1%) is removed from the as-grown (AG) samples following a post-annealing process (reduction) [1,2,3,4,5]? In fact, the AG samples, even with sufficient electron-doping by adding Ce, are antiferromagnetic (AF) insulators at low temperature. Far from being a simple materials issue, the understanding of the microscopic origin of the reduction process that triggers superconductivity may shed light on other related questions in high-Tc superconductivity.Long considered as the microscopic explanation of the reduction process, the removal of extraneous oxygen atoms located above Cu (apical oxygen) has been ruled out by recent Raman and crystal-field infrared transmission studies [6,7]. Indeed, these studies revealed two main defects appearing with the oxygen reduction, which have been tentatively assigned to out-of-plane and inplane oxygen vacancies, the latter being the only one observed at optimal doping. In parallel, a (RE,Ce) 2 O 3 impurity phase epitaxial to the CuO 2 planes appears in reduced superconducting samples but disappears in reoxygenated nonsuperconducting samples [8,9,10,11]. Based on this phenomenon, it has been proposed recently that the Cu excess released during the formation of the (RE,Ce) 2 O 3 impurity phase fills Cu vacancies and makes the remaining structure more stoichiometric [11]. Which of these structural defects has the most significant impact on the electronic properties is still under intense debate * Electronic address: richarpi@bc.edu and calls for a better characterization of the electronic band structure before and after the reduction process. In contrast to the widespread belief that the reduction process in the electron-doped cuprates can be considered as an independent degree of freedom for carrier doping, a recent systematic study of the Hall coefficient in Pr 2−x Ce x CuO 4 thin films with various oxygen contents showed that the carrier mobility rather than their concentration is modifie...

Doping evolution and polar surface reconstruction of the infinite-layer cuprateSr1−xLaxCuO2

“…5 describes, this unusual Fermi surface is due to strong (π, π) antiferromagnetism, which gaps the quasiparticles near (π/2, π/2). Recent studies of the Re 2−x Ce x CuO 4 family have shown a clear link between oxygen content and the gapping of portions of the Fermi surface by antiferromagnetism [22][23][24] . Chemical and structural similarities between the two families strongly suggests that the energy pseudogap near (π/2, π/2) observed for Sr 0.90 La 0.10 CuO 2 may also be due to incomplete oxygen reduction.…”

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

“…Effects of annealing are still not fully understood on the microscopic level: a small amount of oxygen atoms at the apical oxygen site1112, which stabilize the AFM ordering, and/or those at the regular site (in the CuO 2 plane or the LnO (Ln: rare earth) layer)13 are possibly removed by reduction annealing, while the discovery of secondary phase of Ln 2 O 3 created by annealing14 raised the possibility that annealing mends Cu defects existing in the as-grown sample by forming the Ln 2 O 3 phase1516. Previous ARPES studies have revealed that reduction annealing decreases the intensity of the AFM-folded bands and increase the spectral intensity at Fermi level ( E F )1718, but the AFM pseudogap has been seen in all the e-HTSCs from the underdoped to overdoped regions studied so far19. Therefore, the AFM pseudogap has been regarded as a hallmark of the e-HTSCs and the relationship between antiferromagnetism and superconductivity has been considered as a more essential ingredient of the e-HTSCs than the hole-doped ones.…”

Terahertz magnetotransport measurements in underdopedPr2−xCexCuO4and comparison with angle-resolved phot

“…From the published ARPES data, reasonable values of the size and shape of the FS as well as the edge and corner Fermi velocities and scattering rates for excitation energies near the FS (below the observed kink in the energy dispersion) 17 are summarized in Table I for 10% and 12% doping levels. It should be noted that only one study reports the corner Fermi velocity where v c ∼ 0.4v e .…”