Research

Overview

Atomic-resolution cryogenic electron microscopy of low temperature trimers in a 2D material

Quantum materials host a myriad of fascinating structural, electronic and magnetic ground states as well as complex behaviors ranging from the nanoscale coexistence of competing phases to a huge sensitivity to external stimuli. Our laboratory utilizes in situ electron microscopy to visualize and manipulate these materials at the atomic scale.

Techniques

The instrument at the heart of our research is the scanning transmission electron microscope (STEM) which provides vivid atomic-resolution images of crystalline materials. To access and manipulate the rich phases of quantum materials, both ultra-stable cryogenic sample holders and in situ control knobs are essential.

High-resolution cryogenic STEM imaging near 90 K has recently been demonstrated, enabling unprecedented microscopic insights such as the direct visualization of the picometer scale distortions that accompany charge and orbital order. More exotic low temperature phenomena remain to be explored.

In our lab, we strive to couple cryogenic STEM imaging (down to liquid helium temperatures) with in situ and ex situ electrical excitation. This combination will allow us to not only correlate atomic-scale insights with the macroscopic electronic properties of quantum materials but also to induce novel phenomena in these materials.

Map of atomic displacements in a charge-ordered material

Picometer-scale atomic displacements in the charge order phase of manganites

Topics

The materials we study range from bulk complex oxides to atomically engineered heterointerfaces to quasi-2D and quasi-1D compounds. These systems constitute rich playground for studying phenomena such as charge and orbital order, superconductivity, phase separation, ferroelectricity and quantum criticality.

We are also interested in understanding phase transitions by directly visualizing order and disorder. For example, through real space observations of topological defects in charge-ordered stripes, we revealed how phase fluctuations alter long range ordering.

Building on this, our lab is developing a platform to image non-equilibrium transitions and metastable states driven by electrical current and/or light pulses.

Metastable charge density wave domains in a 2D material

Latest Posts

Variable temperature cryogenic STEM shown by Noah from Cornell

Noah Schnitzer (Cornell) et al demonstrate the use of a cryogenic MEMS-based system that achieves intermediate cryogenic temperature. This allows for the first time atomic-resolution STEM imaging and picometer precision mapping as a function of temperature, a key capability for understanding the evolution of order. Even more impressive, the results here show that we can track order in the exact same field of view across temperature, registered unit cell to unit cell. This allows tracking of topological defects in charge order and how they lead to melting of order. Read the pre-print here.

Our lab demonstrates a novel liquid helium TEM capability

Our team has been working on a novel design that enables liquid helium cooling inside transmission electron microscopes. This long-sought capability is key to accessing quantum phenomena but had proven difficult to achieve. Using a novel design, we demonstrate ultra-cold TEM performance (23 K), impressive millikelvin temperature stability, and low vibrations that enable atomic resolution TEM imaging. For more details check out our manuscript .

Suk Hyun Sung Joins the Lab

Suk Hyun Sung joins the lab at the Rowland Institute at Harvard. He brings immense experience in 2D materials, electron microscopy, and in situ experiments. Welcome Suk Hyun!