Ho Nyung Lee

Quantum Materials Synthesis | Advanced Characterization

Projects and Teams

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Precision Synthesis of Quantum and Energy Materials

Development of novel hybrid quantum materials and heterostructure by PLD and MBE for spintronics and quantum information science​

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Emerging Quantum Phenomena and Physics of Symmetry, Correlation, Topology

Exploiting, controlling, and understanding symmetry, strong electron correlation and topology to search for novel correlated and topological quantum materials.

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Interface Physics and Hybrid Materials

Creating, understanding, and controlling Interfaces for novel electronic, magnetic, and ionic functionalities

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Energy Materials - Functional Defects, Electrochemical and Ionic Oxides, and Oxygen Sponges

Oxide based energy materials research includes kinetic and thermodynamic understanding of oxygen vacancy formation and strain control of oxygen vacancy formation in complex oxides

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Strain Engineering for Novel Phenomena and Improved Performance

Strain engineering is a unique strategy for epitaxial thin films  to improve the physical properties or electrochemical activities. This approach is being applied for various class of complex oxide thin films and heterostructures

Precision Synthesis of Quantum and Energy Materials

A grand challenge for materials science is to design materials with tailored functionality. The controlled synthesis of a wide variety of oxide crystals via epitaxial growth is a powerful way to design thin films and heterostructures with atomic level precision, allowing us to produce materials with remarkable physical properties and functionalities. Spurred by recent advances in the synthesis of such artificial materials at the atomic scale, the physics of oxide heterostructures containing atomically smooth layers of such correlated electron materials with abrupt interfaces is a rapidly growing area. Thus, we have established a growth technique to control complex oxides at the level of unit cell thickness by pulsed laser epitaxy. The atomic-scale growth control enables to assemble the building blocks to a functional system in a programmable manner, yielding many intriguing physical properties that cannot be found in bulk counterparts. Functional complex-oxides display a wide spectrum of physical properties, including dielectricity, ferroelectricity, piezoelectricity, ferromagnetism, (semi)conducting behavior, and superconductivity. This class of functional materials, especially in forms of thin films and heterostructures, is strategically and industrially important and offers a wide range of opportunities for electronic, magnetic, piezoelectric, and thermoelectric applications, such as sensors, actuators, quantum computing, information storage, and energy storage and utilization. Specifically, our objectives are (1) to create functionalities in complex oxides by epitaxial stabilization, (2) to control order parameters, such as spin, electron, charge, and lattice, in interfacial materials to achieve novel functionalities, and (3) to understand topology and related quantum phenomena for advancing quantum materials for quantum information science. This is conducted by two epitaxial growth techniques: pulsed laser epitaxy of complex oxides and molecular beam epitaxy of chalcogenites and other metal-based topological materials.  

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Emerging Quantum Phenomena and Physics of Symmetry, Correlation, and Topology

 

We study to understand the role of symmetry, strong electron correlation and topology on exotic physical phenomena to search for innovative quantum materials. The current focus is on controlling and utilizing symmetry, correlation, and topology to find many exotic quantum phenomena, such as skyrmions and quantum anomalous Hall effect. Correlated topological materials are also of interest based on recent investment on spin- and laser-ARPES as well as MBE.  

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Physics of Oxide Interfaces and Hybrid Materials

Complex oxides are known to possess the full spectrum of fascinating properties, including magnetism, colossal magneto-resistance, superconductivity, ferroelectricity, pyroelectricity, piezoelectricity, multiferroicity, ionic conductivity, and more. This breadth of remarkable properties is the consequence of strong coupling between charge, spin, orbital, and lattice symmetry. Advanced epitaxial growth techniques have enabled the synthesis of nearly perfect thin films, superlattices, etc. by the atomic- control of surfaces and interfaces led to the successful growth of epitaxial superlattices containing thousands of individual layers (up to one micron) with extraordinary crystalline quality. This capability now allows us to synthesize entirely artificial layered materials that do not exist in nature and to explore unprecedented physical properties. Based on the atomic-scale synthesis capability, my current research focuses principally on understanding, controlling, and ultimately designing epitaxial complex oxide thin films and heterostructures to obtain novel functionalities.  Exploring and discovering new functionally cross-coupled complex oxides and their heterostructures through understanding and controlling the structure, composition, electronic structure, and chemistry of heterointerfaces are the core of my research interests. 

 

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Energy Materials – Functional Defects, Ionic Oxides, and Oxygen Sponges

Fast, reversible redox reactions in solids at low temperatures without thermomechanical degradation are a promising strategy for enhancing the overall performance and lifetime of many energy materials and devices. However, the robust nature of the cation’s oxidation state and the high thermodynamic barrier have hindered the realization of fast catalysis and bulk diffusion at low temperatures. Thus, we focus on understanding and developing novel oxide based energy materials for high performance electrochemical energy generation and storage devices as well as low-temperature cathode materials. Strain coupling has been one of the main approaches to understand and control the energetics of oxygen vacancy formation and migration. While diverse aspects of perovskite oxides for use in, e.g., energy generation and storage, has not been much exposed, our recent accomplishments listed below provide examples of great potential of oxide materials to accelerate innovations in energy science and technology. 
 
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Strain Engineering of Oxide Thin Films 

Epitaxial strain, induced in thin films due to lattice mismatch between the material and the substrate, results in enhanced properties and device performance for many materials. Examples include a higher operation speed and lower power consumption in strain-engineered semiconductor-based devices and a large enhancement of ferroelectric and dielectric responses in certain complex oxide perovskites as well as superconducting transition temperatures. Therefore, epitaxial strain is recognized as a useful tool to influence materials properties and it induces not only structural modifications, but also exchange kinetics and thermodynamic stabilities of oxygen, making it as a useful tool to vary the performance of functional and energy materials. While it was originally known for its ability to structural control, but recent studies unveiled that such structural instability is also associated with the change in kinetic and thermodynamic responses to strain as well. Thus, our research focuses on understanding the complex, coupled effects of strain on various classes of materials to better understand the potential of strain engineering beyond its mechanical control of matter.
 
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