Accelerating quantum materials development with advances in transmission electron microscopy

TL;DR: In this paper , the authors describe how progress in the field of electron microscopy (EM), including in-situ and in-operando-EM, can accelerate advances in quantum materials.

Abstract: Quantum materials are driving a technology revolution in sensing, communication, and computing, while simultaneously testing many core theories of the past century. Materials such as topological insulators, complex oxides, superconductors, quantum dots, color center-hosting semiconductors, and other types of strongly correlated materials can exhibit exotic properties such as edge conductivity, multiferroicity, magnetoresistance, superconductivity, single photon emission, and optical-spin locking. These emergent properties arise and depend strongly on the material’s detailed atomic-scale structure, including atomic defects, dopants, and lattice stacking. In this review, after the introduction of different classes of quantum materials and quantum excitations, we describe how progress in the field of electron microscopy (EM), including in-situ and in-operando-EM, can accelerate advances in quantum materials. Our review describes EM methods including: i) principles and operation modes of EM; ii) EM spectroscopies, such as electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and electron energy gain spectroscopy (EEGS); iii) four-dimensional scanning transmission electron microscopy (4D-STEM); iv) dynamic and ultrafast EM (UEM); v) complimentary ultrafast spectroscopies (UED, XFEL); and vi) atomic electron tomography (AET). We discuss how these methods inform structure-function relations in quantum materials down to the picometer scale and femtosecond time resolution, and how they enable precision positioning of atomic defects and high-resolution manipulation of quantum materials. Among numerous notable results, our review highlights how EM has enabled identification of the 3D structure of quantum defects; measuring reversible and metastable dynamics of quantum excitations; mapping exciton states and single photon emission; measuring nanoscale thermal transport and coupled excitation dynamics; and measuring the internal electric field and charge density distribution of quantum heterointerfacesall at the quantum materials’ intrinsic atomic and near atomic-length scale. We conclude by describing open challenges for the future, combining ultralow temperature (below 10K) with atomic spatial resolution and meV energy resolution. With atomic manipulation and ultrafast characterization enabled by EM, quantum materials will be poised to integrate into many of the sustainable and energy-efficient technologies needed for the 21st century.