MIT physicists have built a new microscope that can see quantum motion inside superconductors using terahertz light.
The advance lets scientists observe electronic behavior that remained hidden for decades.
Terahertz radiation sits between microwaves and infrared on the electromagnetic spectrum. Its frequency matches how atoms and electrons naturally vibrate inside materials.
Yet its long wavelength has made it nearly useless for studying microscopic samples.
Now, researchers at MIT have found a way to overcome that limitation. Their terahertz microscope compresses long terahertz waves into a microscopic spot.
The result is a tool that can directly resolve quantum-scale motion in solid materials.
Breaking diffraction barrier
Terahertz light oscillates at trillions of cycles per second. That frequency makes it ideal for probing quantum vibrations. But terahertz waves stretch hundreds of microns long.
Physics limits how tightly light can be focused. As a result, conventional terahertz beams wash over tiny samples.
“Our main motivation is this problem that, you might have a 10-micron sample, but your terahertz light has a 100-micron wavelength,” says Alexander von Hoegen.
“You would be missing all these quantum phases that have characteristic fingerprints in the terahertz regime.”
To bypass this limit, the team used spintronic emitters. These devices consist of stacked ultrathin metal layers.
When struck by a laser, electrons inside the layers generate sharp pulses of terahertz radiation.
The researchers placed samples extremely close to the emitter.
This trapped the terahertz field before it spread out. In this near-field regime, the light bypasses the diffraction limit and probes nanoscale features.
The team integrated the spintronic emitter into a full microscope design.
They paired it with a Bragg mirror that filters unwanted wavelengths.
The mirror shields samples from the laser that triggers terahertz emission.
This setup allowed the researchers to study delicate materials without damaging them.
The microscope can now scan microscopic regions while preserving terahertz sensitivity.
As a test case, the team examined an atomically thin sample of bismuth strontium calcium copper oxide, or BSCCO.
The material becomes superconducting at relatively high temperatures.
The researchers cooled the sample near absolute zero. They then scanned it with terahertz pulses while recording how the field changed after passing through.
“We see the terahertz field gets dramatically distorted, with little oscillations following the main pulse,” von Hoegen says.
“That tells us that something in the sample is emitting terahertz light.”
Seeing superconducting motion
Further analysis revealed the source of the signal. The microscope captured collective oscillations of superconducting electrons.
These electrons form a frictionless superfluid inside the material.
“This new microscope now allows us to see a new mode of superconducting electrons that nobody has ever seen before,” says Nuh Gedik.
Physicists have long predicted such motion. Until now, no instrument could directly visualize it at terahertz frequencies.
Beyond superconductivity, the microscope could impact wireless technology.
Terahertz frequencies promise faster data transmission than today’s microwave systems.
“There’s a huge push to take Wi-Fi or telecommunications to the next level, to terahertz frequencies,” von Hoegen says.
“If you have a terahertz microscope, you could study how terahertz light interacts with microscopically small devices.”
The team now plans to apply the microscope to other two-dimensional materials.
Many fundamental excitations occur in the terahertz range.
For the first time, scientists can zoom in and watch them unfold.
The study is published in the journal Nature.