Physicists go to extremes to capture quantum materials - Harvard Gazette

"Cryogenic transmission electron microscopy - TEM - has long played a vital role in many branches of science, from biology to physics, because the very low temperatures allow close examination of samples of everything from inorganic crystals to complex biomolecules at the atomic scale. Typically, the cryogen, or cooling agent, is liquid nitrogen, which boils at 321 below zero Fahrenheit (or 77 Kelvin) - impressive, but not cold enough to see those strange quantum wriggles."

"That's why scientists have strived over the last decade to go colder by using liquid helium, which boils at 421 below zero Fahrenheit, or 4 Kelvin, and is very close to "absolute zero." But this comes with serious technical problems that affect the mechanical stability of the microscope. Harvard researchers envisioned a new way to use liquid helium for a more stable approach to this high-level microscopy, a breakthrough explained in a paper published last month in PNAS."

"The research is among the first high-impact papers (another was robot flies) since Rowland moved to Harvard's science campus a year ago. The original concept of cryogenic cooling during microscopy to preserve the structure of biological molecules - which led to the 2017 Nobel Prize for chemistry - was to use it to study cells, proteins, and other soft matter."

Researchers at the Rowland Institute and the University of Michigan developed a liquid-helium cooling strategy that achieves much lower temperatures for cryogenic transmission electron microscopy. Cryogenic TEM traditionally uses liquid nitrogen (~77 K), which preserves biological and inorganic samples but cannot reveal quantum effects. Liquid helium (~4 K) approaches absolute zero and can expose quantum behavior but introduces mechanical stability problems for microscopes. The team built a more stable helium-cooled TEM system through engineering innovations and collaborative design, enabling ultra-cold microscopy at sub-atomic resolution. The work was reported in PNAS and represents an advance toward imaging quantum materials with unprecedented clarity.

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