High-TcSuperconductivity at the Interface between theCaCuO2and

D. Di Castro

¹

,

Claudia Cantoni

²

,

F. Ridolfi

³

et al.

Abstract

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low T c . We report the occurrence of high T c superconductivity in the bilayer CaCuO 2 /SrTiO 3 , where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO 2 /SrTiO 3 interface must be realized between the Ca plane of CaCuO 2 and the TiO 2 plane of SrTiO 3 . Only in this case extra oxygen ions can be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO 2 planes. A detailed hole doping spatial profile has been obtained by STEM/EELS at the O K-edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO 2 unit cells close to the interface with SrTiO 3 . The results obtained for the CaCuO 2 /SrTiO 3 interface can be extended to multilayered high T c cuprates, contributing to explain the dependence of T c on the number of CuO 2 planes in these systems. 2The interface between complex transition metal oxides is recently emerging as one of the most interesting systems in condensed matter physics [1]. Indeed, a range of fascinating interface electronic phenomena, as high mobility two-dimensional electron gas, quantum Hall effect, and superconductivity, have all been discovered in oxide hererostructures [2][3][4][5][6][7][8], but are absent in either of their constituents. One interesting example is the formation of a conducting quasi-two-dimensional electron gas at the interface between the insulating perovskites LaAlO 3 and SrTiO 3 [2]. Strikingly, this interface is also superconducting with transition temperature (T c ) about 10 -1 K [4,9].On the other hand, the layered structure of cuprate high T c superconductors (HTS) can be schematized as a sequence of natural interfaces between two blocks with different structure and functionality: an insulating block with "infinite layers" (IL) structure, i.e., containing a sequence of In this work, by using state-of-the-art aberration-corrected scanning transmission electron microscopy (STEM) coupled to electron energy loss spectroscopy (EELS), we investigate the CCO/STO interface present in the bilayer (CCO) n /(STO) m , with unprecedent spatial resolution [16].We find that this interface shows high T c superconductivity, with optimal T c about 40 K, a value smaller, but still comparable with those found in the [(CaCuO 2 ) n /(SrTiO 3 ) m ] N superlattices [6,10]. Wegive direct evidence that charge doping, and therefore superconductivity, are realized through the introduction of extra oxygen ions at the CCO/STO interface, giving rise to a CaO x atomic plane

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

“…The same trend using XMCD to probe Cu magnetism was recently seen for bulk YBCO as a function of doping60, which serves to support the idea that while we are doping via an interface into an ultra YBCO layer, much of the expected bulk physics remains intact. This results from the highly two-dimensional character of the cuprate high temperature superconductors, as was seen by the presence of superconductivity even in isolated CuO 2 layers6162.…”

Spin and charge excitations in artificial hole- and electron-doped infinite layer cuprate superconductors

“…In order to get h-doping of ILs, a different approach is necessary: it takes advantage of recent progresses in epitaxial growth, and is based on a proper engineering of heterostructures and superlattices (SLs) 32,[34][35][36][37] . These synthetic HTS, not constrained to thermodynamic limitations connected with bulk crystal growth, are particularly interesting in the search of increasing T c .…”

Tuning electronic reconstructions at the cuprate-manganite interface

“…In CCO/STO heterostructures the oxygen pressure during the growth process influences the amount of oxygen incorporated at the IFs [8,13,14,29]. In the CCO/STO system, SLs prepared under SOC are superconducting with a T C of up to 50 K [14].…”

“…However, an oxygen redistribution 75 process in the alkaline-earth metal IF planes is more likely 76 since this process was reported for the structurally similar 77 case of CCO/STO SLs [29]. Growth in strongly oxidizing 78 conditions (SOCs) further favors incorporation of oxygen ions 79 in the Ca plane of type-B IFs [8]. This additional oxygen 80 would be apical for Mn and Cu at both sides of the IF [see 81 Fig.…”

“…Particularly oxygen plays a key role in determining surface [2,3] and interface [4][5][6] electronic structure in transition-metal oxide heterostructures. The observation of high-T C superconductivity [7,8] at the IF of insulating cuprates, the magnetic coupling between cuprates and manganites [9], and oxygen redistribution at the IF between infinite-layer cuprates and strontium titanate [10] [11]. In CCO, layers of Cu in fourfold planar oxygen coordination are separated by bare Ca atoms.…”