Nature of oxygen dopant-induced states in high-temperatureBi2Sr2CaCu2O8+

Abstract

We have performed an angular-resolved photoemission study of underdoped, optimally doped and overdoped Bi2Sr2CaCu2O8+x samples using a wide photon energy range (15 -100 eV). We report a small and broad non-dispersive A1g peak in the energy distribution curves whose intensity scales with doping. We attribute it to a local impurity state similar to the one observed recently by scanning tunneling spectroscopy and identified as the oxygen dopants. Detailed analysis of the resonance profile and comparison with the single-layered Bi2Sr2CuO6+x suggest a mixing of this local state with Cu via the apical oxygens.PACS numbers: 74.72. Hs, 74.25.Jb, In contrast to pure systems, the carrier density of the CuO 2 planes in the cuprates can only be modified by creating nonstoichiometric defects in the parent compounds. For example, Bi 2 Sr 2 CaCu 2 O 8+x (Bi2212) is hole-doped mainly by the introduction of an extraneous amount of oxygens, which is estimated to be around x=0.16 per formula unit for the T c = 95 K optimally doped samples [1]. Such dopants have long been suspected to induce local electronic disorder [2]. However, it is only recently that scanning tunneling spectroscopy (STS) measurements established their in-plane positions in the structure by correlating the STS spectra to the local electronic disorder as a function of doping [3]. In particular, the differential conductance at the oxygen dopant (O δ ) site is characterized by a broad peak around -0.96 eV. This peak is observed in ∼ 8Å diameter regions and their number is found to be proportional to doping [3]. Surprisingly, larger superconducting gap magnitudes accompanied with the absence of coherent peaks are observed in these regions, suggesting that the O δ are correlated to the CuO 2 planes electronic properties. Due to the importance of this issue, it is necessary to confirm the existence of that coupling and to investigate further the local impact of the O δ . Owing to its complementarity with STS, APRES is certainly an appropriate tool to investigate this issue. More importantly, the atomic selectivity of the resonant ARPES measurement provides unique and valuable insight concerning the wavefunction of the states of interest. When the incident photon energy is tunned to near an absorption edge of a specific element, a resonance (strong enhancement of photoelectron emission) usually occurs for certain valence spectral features that involve this element. This "element-resolved" capability may shed light on the nature of wavefunctions at the O δ * Electronic address: richarpi@bc.edu site and its influence to local superconducting properties.In this letter, we present an ARPES study of Bi2212 which reveals a small, broad and non-dispersing peak corresponding to a localized state analogous to the one reported recently by STS at -0.96 eV [3]. We show that the spectral weight of the corresponding ARPES peak increases with doping, thus reinforcing its relation to the presence of O δ . In order to characterize further this feature, we report measurements obtained ...

Orbital characters determined from Fermi surface intensity patterns using angle-resolved photoemission spectroscopy

“…As with other probes, symmetry plays an important role in the photoemission process. It has been used often in the past to identify the nature of the electronic states of various systems [1][2][3][4][5][6][7].…”

Phase transitions to dipolar clusters and charge density waves in high T c superconductors

“…[9] The found resonance profile of the corresponding nondispersive peak indicates an unexpected mixing with Cu states. The A 1g symmetry of the peak suggests that the oxygen dopant-induced states are mixed with Cu through the O dopant -O apex 2 p z -Cu 3 d 3z 2 −r 2 channel.…”

“…The A 1g symmetry of the peak suggests that the oxygen dopant-induced states are mixed with Cu through the O dopant -O apex 2 p z -Cu 3 d 3z 2 −r 2 channel. [9] Experiments indicate that the doped cuprates have a mixture of characters. To see this, we start with an undoped parent compound such as La 2 CuO 4 .…”

“…The inhomogeneity of cuprate superconductors coupled with dopant atoms is well documented besides LCO also in other materials and in different experiments using scanning tunneling spectroscopy [4,5,6,7,8], photoemission spectra (ARPES) [9] -suggesting that the oxygen dopant-induced states are mixed with Cu atoms -and measurements of dielectric constant [10] etc.…”

The VUV/IR/THz free electron laser program at Jefferson Lab

“…Such techniques will bring new dimensions to spectroscopy and imaging, as well as allowing studies of out of equilibrium dynamics. A unique application of the JLab VUV source is photoemission studies at higher energy and momentum resolution of highly correlated systems such as high T c materials [10]. Emitted electron energy and momentum analysis can be done conventionally by dispersion, but can also be done using time of flight techniques, which offer resolution advantages.…”