© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 3357 www.advmat.de www.MaterialsViews.com wileyonlinelibrary.com COMMUNICATION Vu Thanh Tra, Jhih-Wei Chen, Po-Cheng Huang, Bo-Chao Huang, Ye Cao, Chao-Hui Yeh, Heng-Jui Liu, Eugene A. Eliseev, Anna N. Morozovska, Jiunn-Yuan Lin,* Yi-Chun Chen, Ming-Wen Chu, Po-Wen Chiu, Ya-Ping Chiu, Long-Qing Chen, Chung-Lin Wu,* and Ying-Hao Chu Ferroelectric Control of the Conduction at the LaAlO 3 / SrTiO 3 Heterointerface V. T. Tra, Prof. J.-Y. Lin Institute of Physics National Chiao Tung University Hsinchu, 30010, Taiwan, ROC E-mail: ago@nctu.edu.tw J.-W. Chen, Prof. Y.-C. Chen, Prof. C.-L. Wu Department of Physics National Cheng Kung University Tainan, 70101, Taiwan, ROC E-mail: clwuphys@mail.ncku.edu.tw P.-C. Huang, B.-C. Huang, Prof. Y.-P. Chiu Department of Physics National Sun Yat-Sen University Kaohsiung, 80424, Taiwan, ROC Y. Cao, Prof. L. Q. Chen Department of Materials Science and Engineering Pennsylvania State University University Park, PA 16802, USA DOI: 10.1002/adma.201300757 Complex oxide heterointerfaces have emerged as one of the most exciting subjects in condensed matter, owing to their unique physical properties and new possibilities for next-gen- eration electronic devices. [1,2] In the push for practical applica- tions, it is desirable to have the ability to modulate the interface functionalities by an external stimulus. In this Communica- tion, we propose a generic approach in which a functional layer is inserted into the heterostructure to acquire non-vola- tile control of the intriguing properties at oxide interfaces. The LaAlO 3 /SrTiO 3 (LAO/STO) interface serves as a model system in which a highly mobile quasi-two-dimensional elec- tron gas (2DEG) forms between two band insulators, [3,4] exhib- iting 2D superconductivity [5] and unusual magnetotransport properties. [6] Although a modulation of the carrier density and mobility of the LAO/STO interface has been achieved using the electric field effect, [7–9] it is essential to extend the control concepts to gain non-volatile and reversible capabilities for practical applications. Recently, non-volatile modification of the local conduction at the LAO/STO interface has been dem- onstrated by scanning probe techniques. [10–12] Several possible mechanisms have been proposed to explain this interesting behavior based on the electrostatic effects attributed to either induced ferroelectricity or surface charge. [13,14] In the study reported here, we added a ferroelectric Pb(Zr 0.2 Ti 0.8 )O 3 (PZT) layer near the LAO/STO interface. The ferroelectric polariza- tion of the PZT layer serves as a control parameter to modulate the 2DEG conducting behavior. The as-grown polarization ( P up state) leads to charge depletion and consequently low conduc- tion. Switching the polarization direction ( P down state) results in charge accumulation and enhances the conduction at the LAO/STO interface. The origin of this modulation is attributed to a change in the electronic structure due to the ferroelectric polarization states, evidenced by X-ray photoelectron spectros- copy (XPS) and cross-sectional scanning tunneling microscopy/ spectroscopy (XSTM/S). Control of the conduction at this oxide interface suggests that the concept can be generalized for other oxide systems to design functional interfaces. In order to understand the influence of ferroelectricity on the LAO/STO interface experimentally, we first carried out electrical transport measurements on the heterostructure ( Figure 1a), in which the PZT layer with the spontaneous polar- ization P PZT functions as a polarized dielectric slab to modu- late the conduction of the LAO/STO heterointerface. Figure 1b shows the sheet resistance versus temperature ( R– T curves) of the PZT/LAO/STO samples with various PZT layer thick- nesses (0–40 nm), while the LAO thickness was fixed (6 u.c., where u.c. stands for unit cell). The R– T curves for these sam- ples show that the sheet resistance at room temperature is low (ca. 23 k Ω/sq) and decreases with temperature, showing metallic behavior. For the samples with PZT on top, the ferro- electric effect sets in and the sheet resistance starts increasing with PZT thickness, showing the strong impact of the intrinsic C.-H. Yeh, Prof. P.-W. Chiu Department of Electrical Engineering National Tsing Hua University Hsinchu, 30013,Taiwan, ROC E. A. Eliseev, Prof. A. N. Morozovska Institute of Problems of Material Sciences and Institute of Physics National Academy of Science of Ukraine Kiev, Ukraine Prof. M.-W. Chu Center for Condensed Matter Sciences National Taiwan University Taipei, 10617, Taiwan, ROC Dr. H.-J. Liu, Prof. Y. H. Chu Department of Materials Science and Engineering National Chiao Tung University Hsinchu, 30010, Taiwan, ROC Adv. Mater. 2013, 25, 3357–3364