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

Abstract

We use angle-resolved photoemission spectroscopy to study the doping evolution of infinite-layer Sr1−xLaxCuO2 thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of the superconducting cuprate parent compounds. As carriers are added to the system, a continuous evolution from charge-transfer insulator to superconductor is observed, with the initial lower Hubbard band pinned well below the Fermi level and the development of a coherent low-energy band with electron doping. This two-component spectral function emphasizes the important role that strong local correlations play even at relatively high doping levels. Electron diffraction probes reveal a p(2 × 2) surface reconstruction of the material at low doping levels. Using a number of simple assumptions, we develop a model of this reconstruction based on the polar nature of the infinite-layer structure. Finally, we provide evidence for a thickness-controlled transition in ultrathin films of SrCuO2 grown on nonpolar SrTiO3, highlighting the diverse structural changes that can occur in polar complex oxide thin films.

Electron Doping of the Parent CuprateLa2CuO4without Cation Substitution

“…1b, we show the Fermi surface of as-grown T -La 2 CuO 4 synthesized in 1 × 10 −7 torr of distilled O 3 , which shows clear weight at E F and a well-defined Fermi surface, unexpected for a nominally undoped Mott insulator. In contrast, ARPES measurements on single crystals of undoped T -Nd 2 CuO 4 [27] as well as thin films of SrCuO 2 [28] show the expected insulating behavior qualitatively consistent with their T -phase counterparts, with no appreciable spectral weight near E F and well-defined lower Hubbard bands.…”

Ground states of bilayered and extended t-J-U models

“…For a realistic electron-hole doping asymmetric band, a nodeless dSC appears on the electron doped side at higher doping densities, and therefore it can be more accessible by experimental probes. This nodeless dSC may have been observed long ago in the magnetic penetration depth in some electron doped monolayered cuprates [40][41][42][43], and recently in the ARPES for an electron doped infinitely-layered cuprate Sr 1−x La x CuO 2 (SLCO) [37,79]. More recently, a nodeless dSC may also have been observed in a hole doped monolayered La-214 cuprate in the highly UD regime [34].…”

“…The SC in these hole doped cuprates are usually found to be stronger, than the SC in these electron doped cuprates [28,40]. Moreover, the stronger the SC in such a hole doped cuprate, the larger the curvature in its Fermi surface [32][33][34][35][36][37][38][39]. There are experiments indicating a coexistence of AFM and SC in some of these hole doped cuprates in the UD regime [51][52][53] doped cuprates in the UD regime [54][55][56].…”

“…When a t-J -U model is extended by hoppings derived from the angle-resolved photoemis-E-mail address: kkvoo@mail.oit.edu.tw. sion spectroscopy (ARPES) [32][33][34][35][36][37][38][39], some contrasting features in the hole and electron doped cuprates can be accounted. For example, the nodeless d-wave superconductivity (dSC) in the magnetic penetration depth in some electron doped cuprates [16,[40][41][42][43][44].…”

Surface atomic structure of epitaxialLaNiO3thin films studied byin situLEED-I(V)

“…In this work, we utilize LEED-I (V ) to perform structural refinements of the surface atomic structure of epitaxial thin films of LaNiO 3 grown by MBE. By benchmarking our results against measurements obtained by COherent Bragg Rod Analysis (COBRA) of synchrotronbased surface x-ray diffraction data 12 , we demonstrate the strong sensitivity of LEED-I (V ) to structural distortions and its potential as a flexible, in situ tool to accurately determine the surface atomic structure of epitaxial thin films of complex materials, especially in situations where a polar discontinuity could dramatically alter the surface electronic structure 13,14 .…”