Charge ordering (CO), characterized by a periodic modulation of electron density and lattice distortion, has been a fundamental topic in condensed matter physics, serving as a potential platform for inducing novel functional properties. The charge-ordered phase is known to occur in a doped system with high d-electron occupancy, rather than low occupancy. Here, we report the realization of the charge-ordered phase in electron-doped (100) SrTiO3 epitaxial thin films that have the lowest d-electron occupancy i.e., d1-d0. Theoretical calculation predicts the presence of a metastable CO state in the bulk state of electron-doped SrTiO3. Atomic scale analysis reveals that (100) surface distortion favors electron-lattice coupling for the charge-ordered state, and triggering the stabilization of the CO phase from a correlated metal state. This stabilization extends up to six unit cells from the top surface to the interior. Our approach offers an insight into the means of stabilizing a new phase of matter, extending CO phase to the lowest electron occupancy and encompassing a wide range of 3d transition metal oxides.
This work was supported by the National Research Foundation of Korea through the Basic Science Research Program (NRF\u22122022R1A2C2004868) and KISTI Supercomputing Center (KSC\u22122019-CRE-0113). This research is funded by the Gordon and Betty Moore Foundation\u2019s EPiQS Initiative, grant GBMF9065 to C.B.E., Vannevar Bush Faculty Fellowship (N00014\u221220-1\u22122844 (C.B.E.)). Transport measurement at the University of Wisconsin\u2013Madison was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), under award number DE-FG02-06ER46327. The authors acknowledge partial support of this research by NSF through the University of Wisconsin Materials Research Science and Engineering Center (DMR\u22122309000). K.E. would like to acknowledge the support by National Research Foundation of Korea through the Basic Research Program (NRF-2022R1C1C2010693). S.O. would like to acknowledge the support by National Research Foundation of Korea through the Basic Research Program (NRF-2021R1I1A1A01058779). I.S. and Y.S.L. would like to acknowledge the support by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2021R1A6A1A10044154). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The STEM work by J.S. and S.H.O. was supported mainly by the Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-MA1702-01 and partly by the National Research Foundation of Korea (NRF) funded by the Korea government (MSIT) (No. NRF-2020R1A2C2101735), Creative Materials Discovery Program (NRF-2019M3D1A1078296), the KENTECH Research Grant (KRG2022-01-019). J.J. and S.Y.C. acknowledge the support by Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Education (2020R1A6C101A202) and National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2023-00258227). H. L. acknowledges the support by National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2021R1A4A1032085).
