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Xiaofeng Qian

2D multiferroics with coupled primary ferroic orders, i.e.ferroelectric, ferromagnetic, ferroelastic, and ferrotoroidicity, possess rich physics and applications, e.g. nanoscale transducers, actuators, photovoltaics, and nonvolatile memories. However, ideal low-dimensional multiferroics are limited by stringent symmetry, thermodynamics, kinetics, and strong coupling criteria required for cross-control of polarization, magnetization, and strain for practical applications. Recent studies from Dr. Qian’s group and other groups demonstrated the possibility of achieving ferroicity/multiferroicity in 2D materials within an ultimate thickness of one to a few nanometers. This opens up exciting yet largely-underexploited quantum processes that may strongly couple multiple physical degrees of freedom with ferroic orders (Figure 1). We hypothesize that the combined first-principles theory and atomistic simulation approach will enable microscopic understanding of coupled quantum processes in 2D multiferroics, and generalize rational principles to discover and design novel multiferroics for multifunctional device applications.

Research Plan:
The REU students will work with Dr. Qian and his graduate students to understand the fundamentals of coupled quantum processes in emergent 2D multiferroic materials involving ferroic orders, spin, charge, orbital, and valley degrees of freedom, understand their influence on optical, electronic, and transport properties, and explore their transformative potentials for energy and device applications. The students will learn first-principles techniques and apply the tools to investigate electronic structure properties including band structure, quantum transport, quasiparticle and exciton excitations, etc. (week 1-4). They will be also guided to study the ferroic orders and compute elastic strain, magnetization, and spontaneous electric polarization through Berry phase approach week 5-7). The students will then work with Dr. Qian and the graduate students to analyze the intrinsic coupling between the calculated electronic structures and ferroic orders (week 8-10).  Among the 10-week REU program, the students will be using trained in using linux workstations and supercomputing clusters and programming Python and Bash scripts to generate input files, post-process the data, analyze the results, and control simulation jobs on supercomputing clusters. The obtained new knowledge will be used to generalize discovery strategies and design principles for novel 2D multiferroics and cultivate novel energy applications and device concepts such as 2D ferroelectric excitonic photovoltaics and ferroelectric memory with ultra-low energy consumption.