This image shows a spin-polarized chromium tip being scanned over a pristine superconducting area with a magnetic order known as C2, in which electron pairs are shown as coupled red spheres. The spin current through the tip induces the C4 magnetic order (yellow and blue tiles) with suppressed superconductivity because the spin fluctuations can no longer mediate electron pairing, shown as decoupled red spheres. Image: KAIST.Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have discovered a way to flip an iron-based superconductor between superconducting and non-superconducting states using a type of electron microscopy. Their approach, which is reported in a paper in Physical Review Letters, involves applying spin-polarized and non-polarized currents to locally change the magnetic order in the sample.
Led by Jhinhwan Lee in the Department of Physics, the researchers identified a basic physical principle that could be used to control superconductivity and to implement novel magnetic memory at the atomic level. This study is the first to demonstrate this type of control, as well as the first direct atomic-scale demonstration of the correlation between magnetism and superconductivity.
The researchers used a spin-polarized scanning tunneling microscope (SPSTM), which works by passing an atomically-sharp metal tip over the surface of a sample, to control and observe the magnetic and electronic properties. They also introduced new ways to perform SPSTM by using an antiferromagnetic chromium tip. An antiferromagnet is a material in which the magnetic fields of its component atoms are ordered in an alternating up-down pattern. This ensures the material has no overall magnetic field, which is essential for preventing the SPSTM tip from destroying the local superconductivity of the sample.
To study the connection between a specific magnetic order known as C4 and the suppression of superconductivity, the team performed high-resolution SPSTM scans of the C4 state with chromium tips and compared them with simulations. Their results led them to suggest that the low-energy spin fluctuations in the C4 state cannot mediate pairing between electrons in the typical band structure of the iron-based superconductor. This is critical because this paring of electrons, defying their natural urge to repel each other, leads to superconductivity.
"Our findings may be extended to future studies where magnetism and superconductivity are manipulated using spin-polarized and unpolarized currents, leading to novel antiferromagnetic memory devices and transistors controlling superconductivity," said Lee
"When designing the experiment, we attempted to implement some decisive features. For instance, we included a spin control function using an antiferromagnetic probe, wide range variable temperature functions that were thought to be impossible in high-magnetic field structures, and multiple sample storage functions at low temperatures for systematic spin control experiments, rather than using simpler scanning probe microscopes with well-known principles or commercial microscopes. As a result, we were able to conduct systematic experiments on controlling magnetism and superconductivity, which competing groups would take years to replicate.
"There were some minor difficulties in the basic science research environment such as the lack of a shared helium liquefier on campus and insufficient university-scale appreciation for large scale physics that inevitably takes time. We will do our best to lead the advancement of cutting-edge science through research projects expanding on this achievement in physical knowledge to practical devices and various technological innovations in measurements."
This story is adapted from material from KAIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.