Profiling the Interface Electron Gas ofLaAlO3/SrTiO3Heterostructures with Hard X-Ray Photoelectron Spectroscopy

Abstract

The conducting interface of LaAlO3/SrTiO3 heterostructures has been studied by hard X-ray photoelectron spectroscopy. From the Ti 2p signal and its angle-dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of LaAlO3 overlayers. Our results point to an electronic reconstruction in the LaAlO3 overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the BerezinskiiKosterlitz-Thouless type.

Nonvolatile Resistive Switching inPt/LaAlO3/SrTiO3Heterostructures

“…In contrast, a two-dimensional nature of the interface transport can be achieved in high-pressure-grown samples, with the electrons being confined a few nanometers near the interface. These transport results are consistent with previous reports on properly oxidized LAO/STO heterostructures [24][25][26]. It is noteworthy that we do not perform any postdeposition annealing in our sample synthesis; thus, as suggested in a recent study [27], oxygen vacancies exist in even the highpressure-grown samples and their contribution to the transport of LAO/STO heterostructures cannot be ignored.…”

“…This mechanism, along with the polar distortion and dipole screening in the LAO overlayers [16], can qualitatively explain the transport properties. In addition, factors like oxygen vacancies [17][18][19] and cation mixing [20][21][22] may influence the characteristics of the electron gas [23][24][25][26][27].…”

Electronic Reconstruction at the Interface Between Band Insulating Oxides: The LaAlO3/SrTiO3 System

“…Core-level photoemission spectroscopy did not detect a sizeable varying electric field with thickness [50]. Signatures of (nominal) Ti 3+ cations were found in insulating (2 uc) as well as conducting (thickness > 4 uc) LAO/STO samples [51]. Finally, the overall fraction of mobile electrons and of electrons in Ti 3+ states was found much lower than the value expected (0.5 e/u.c.)…”

“…Moreover, core-level hard x-ray photoemission (HXPES) experiments have given evidence of the presence of a satellite Ti2p shoulder [51], as shown in Fig. 11a, which is commonly attributed to the emission from Ti ions in a 3+ oxidation state.…”

Reconstructions at complex oxide interfaces

“…These results are different from the results of crystalline LaAlO 3 -SrTiO 3 , for which a clear angle dependence of the Ti 3+ signal has been reported. [84] Additionally, the effect of P O2 on the concentration of Ti 3+ was investigated in Y-ZrO 2 -SrTiO 3 . Only small differences in the Ti 3+ signal were observed between heterostructures grown at 1×10 −6 mbar < P O2 < 1×10 −3 mbar (Fig.…”