A team of researchers at Argonne National Laboratory has developed a groundbreaking technique that allows them to explore quantum behaviour in materials at a tiny scale, just a few nanometers from the surface
This new method creates new avenues for advancing technologies such as superconductors, spintronics and quantum computing.
Cracking open a complex interface
Studying the interface between two materials where they meet and interact has always been a challenge for scientists. These interfaces often hold the key to understanding exotic properties, such as magnetism and superconductivity. However, they are typically buried deep within a sample and only a few nanometers thick, making them nearly impossible to probe using traditional methods.
To combat this long-standing struggle, the research team used a new technique known as surface-sensitive terahertz spectroscopy (SSTS).
SSTS involves directing ultrafast laser pulses through an oxide crystal that’s topped with a thin magnetic film. When the laser hits the interface between the two materials, it generates terahertz vibrations, a form of electromagnetic radiation operating at frequencies approximately 1,000 times higher than those of current 5G wireless networks.
Listening to terahertz vibrations
The researchers focused on capturing these terahertz vibrations because they hold a lot of information about the material’s quantum characteristics. Specifically, they were able to detect what’s known as the TO1 phonon, a type of vibrational mode that is especially sensitive to the material environment near the interface.
What they discovered was that the behaviour of this phonon changed significantly within just 5 nanometers of the interface, compared to how it behaves deeper in the bulk of the material. This suggests that the surface region behaves differently, just like water waves move differently in the shallow versus deep parts of a lake.
This subtle shift in phonon behaviour provides a new way to study and understand complex quantum effects that might otherwise be hidden in traditional experiments.
The future of quantum technologies
One of the most critical aspects of this breakthrough is the sensitivity and versatility of this new technique. Because SSTS can focus precisely on the interface, it allows scientists to study a wide variety of materials and quantum phenomena, not just magnetism but potentially also superconductivity and other elusive states of matter.
Terahertz radiation, in particular, is an exciting tool for this type of research. Not only can it reveal hidden properties in materials, but it may also be capable of triggering entirely new states of matter when it interacts with quantum systems in specific ways.
The future applications of this research
This study was carried out by a collaborative team from Argonne National Laboratory and the University of Washington. The materials were analysed using both terahertz emission spectroscopy and advanced electron microscopy, utilising national facilities supported by the U.S. Department of Energy (DOE).
While the research is still in its early stages, the insights gained from this work could help pave the way for the design of next-generation quantum devices. By providing scientists with a more detailed view of what’s happening at material interfaces, the technique could inform the development of faster, more efficient, and more powerful technologies across various fields.
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