Flexible Nano-mechanical Approaches to Unravelling the Intertwined Orders in Paradigm Oxide Superconductors

Description

The periodic potential set by lattice of materials is the foundation to solid state physics, which not only gives rise to electronic band structure (Bloch’s theorem) but also serves as the starting point to many other subtle energy landscapes, such as energies associated with crystal field splitting, exchange interactions and Jahn-Teller effects, etc., that altogether determine the rich physics of the materials. In transition metal oxides, the sensitive coupling of lattice variations to other degrees of freedom, such as charge, orbital, bond and spin, has enabled a direct manipulation of a variety of competing phases, condensed from often strongly correlated electrons, by lattice strain. This has resulted in the conceptual development of ‘strain engineering’ in complex oxide hetero structures. This project bears interdisciplinary nature as it builds on the following extraordinary scientific and technical advances in recent years: (a) the remarkable nano mechanical response of the hard materials at nanoscale: the 'super elasticity' and 'ultra strength' that otherwise are beyond reach in the bulk counterparts; (b) a burst of significant research discoveries upon the application of a uniaxial strain field enabled by a piezoelectric-stack apparatus, offering previously inaccessibly ways to tuning quantum phase transitions and/or revealing the hidden phases, particularly pertaining to unconventional superconductivity. In this project, we aim to design and develop comprehensive novel (electro-)mechanical setups, which offer the unprecedented capability of employing an extreme strain field at both cryogenic and room temperatures, for manipulation of low-dimensional oxide superconductor membranes. This apparatus/technique takes great advantages of the unique mechanical properties of the oxide superconductors at nanoscales: we leverage the unusual ‘softness’ and flexibility in nano membranes of these otherwise ‘hard’ and brittle materials in their bulk forms. Through this approach, we will for the first time be able to apply unprecedented multi-axes continuous pressure down to the microscopic level; therefore, engineering the ground states and quantum phases of the oxide superconductors at unit-cell scale. Particularly in some model systems, we will uncover novel competing/intertwined orders and carefully examine the relationship of these ordered phases or their fluctuations to unconventional superconductivity that remains long-standing conundrum in many paradigm materials systems. This project offers an important and unparalleled new avenue to addressing key enigmas in superconductivity research.