Special seminar on 2019.08.14(wed) 11:00 AM

Location : 7th floor of Samsung Library

Speaker : Dr. Eun-Mi Choi

3D-strain induced superconductivity in La₂CuO_4+δ using a simple vertically aligned nanocomposite approach

  A long-term goal for superconductors is to increase the superconducting transition temperature, T_C. In cuprates, T_C depends strongly on the out-of-plane Cu-apical oxygen distance, and the in-plane Cu-O distance. High out-of-plane and the in-plane parameters are both individually linked to higher T_C, but to date they have not been achieved together.

Herein, I introduce a simple and unique self-assembled approach to 3D-strain engineering. In simply-grown, self-assembled, vertically aligned thin film nanocomposite (VAN) thin films of La₂CuO_4+δ+LaCuO₃ grown on SrTiO₃, by strongly increasing the out-of-plane distances without reducing in-plane distances, we achieve superconductivity up to 50 K. Our VAN approach leads to strong vertical strain of ~50 nm La₂CuO_4+δ nanopillars by a LaCuO₃ matrix in which the La₂CuO_4+δ is embedded. The LaCuO₃ expands the La₂CuO_4+δ out-of-plane along the interfaces spaced every ~50 nm, the strained region spreading ~10 nm laterally from each interface. A T_C of 50 K has only been achieved before at single atomic layer interfaces in complex heterostructures.­­­­­­ Otherwise, in plain or doped La₂CuO_4+δ films, T_C is 35 K or below. In addition, no additional process to supply excess oxygen, e.g. by ozone annealing, was required as is the case for La₂CuO_4+δ films studied previously. Our work represents a new, self-assembled approach to 3D-strain engineering of cuprates to enhance T_C. Our proof-of-concept work represents an entirely new approach to increasing T_C in cuprates or other superconductors.¹

In addition, I introduce our promising result of weak magnetic signatures of superconductivity up to 120 K from DC magnetic susceptibility measurements, which can be turned on and off by changing oxygen content.

1. Choi, E.-M. et al. 3D strain-induced superconductivity in La2CuO_4+δ using a simple vertically aligned nanocomposite approach. Sci. Adv. 5, eaav5532 (2019).