[Special seminar] Dr. Eun-Mi Choi
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 La2CuO4+δ using a simple vertically aligned nanocomposite approach
A long-term goal for superconductors is to increase the superconducting transition temperature, TC. In cuprates, TC 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 TC, 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 La2CuO4+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 La2CuO4+δ nanopillars by a LaCuO3 matrix in which the La2CuO4+δ is embedded. The LaCuO3 expands the La2CuO4+δ out-of-plane along the interfaces spaced every ~50 nm, the strained region spreading ~10 nm laterally from each interface. A TC of 50 K has only been achieved before at single atomic layer interfaces in complex heterostructures. Otherwise, in plain or doped La2CuO4+δ films, TC 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 La2CuO4+δ films studied previously. Our work represents a new, self-assembled approach to 3D-strain engineering of cuprates to enhance TC. Our proof-of-concept work represents an entirely new approach to increasing TC 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 La2CuO4+δ using a simple vertically aligned nanocomposite approach. Sci. Adv. 5, eaav5532 (2019).