Design and Differentiation of Quantum States at Subnanometer Scale in La2CuO4-Sr2CuO4-δ Superlattices

Nicolas Bonmassar; Georg Christiani; Ute Salzberger; Yi Wang; Gennady Logvenov; Y Eren Suyolcu; Peter A van Aken

doi:10.1021/acsnano.3c01422

Design and Differentiation of Quantum States at Subnanometer Scale in La₂CuO₄-Sr₂CuO_4-δ Superlattices

ACS Nano. 2023 Jun 27;17(12):11521-11526. doi: 10.1021/acsnano.3c01422. Epub 2023 Jun 1.

Authors

Nicolas Bonmassar¹, Georg Christiani¹, Ute Salzberger¹, Yi Wang², Gennady Logvenov¹, Y Eren Suyolcu^{1

3}, Peter A van Aken¹

Affiliations

¹ Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany.
² Center for Microscopy and Analysis, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China.
³ Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States.

Abstract

We present a study on the properties of superlattices made of ultrathin Sr₂CuO_4-δ layers sandwiched between La₂CuO₄ layers beyond the antiferromagnetic insulating nature of the individual layers of choice. Using molecular beam epitaxy, we synthesized these superlattices and observed superconductivity and metallicity at the interfaces. We probed the hole distribution to determine the discernible quantum states and found that the high-quality epitaxy, combined with mapping the electronic fine structure by electron energy-loss spectroscopy, allowed for the differentiation of insulating, metallic, and superconducting layers at the atomic-column scale. Our results demonstrate the possibility of exploring specific electronic properties at the subnanometer scale and highlight the potential of utilizing metastable Sr₂CuO_4-δ slabs.

Keywords: O-K edge prepeak; electron energy-loss spectroscopy; metal−insulator transition; molecular beam epitaxy; oxygen vacancies; scanning transmission electron microscopy; superconductivity.