A repeating 120-degree pattern in voltage response to a rotating magnetic field, long considered a sign of materials with potential for quantum computing or spintronics, can also arise in classical materials, according to new calculations from Kobe University researchers. The findings refine the diagnostic and enable more purposeful design. Kobe University quantum solid state physicist FUSEYA Yuki explains that this research addresses a problem where that isn’t necessarily the case. First author YAMADA Akiyoshi states this research is “a breakthrough that has uncovered a blind spot in both theory and experiment,” providing physicists with sharper tools for material identification and more purposeful design.
Planar Hall Effect Distinguishes Classical and Exotic Materials
Researchers send a current through a flat sample and observe the resulting voltage when exposed to an in-plane magnetic field, analyzing how the voltage pattern changes as the field rotates. In solid-state physics, laws underpinned by symmetry hold true. The team found that a 120-degree rotational symmetry in the voltage pattern, previously linked to unusual quantum behavior, can actually be predicted by extending existing classical theory from 70 years ago. This refines the diagnostic and enables more purposeful design. The researchers found that alignment dictates the threefold component, with applicability across a broad range of materials. Yamada adds, “This study demonstrates that by deciphering the hidden regularities of the electron flow, information regarding microscopic crystal symmetry and electronic structure can be extracted from macroscopic electrical measurements.”
Higher-Order Classical Theory Explains Threefold Symmetry
The search for materials exhibiting exotic quantum properties has long relied on the planar Hall effect as a rapid diagnostic tool, but recent work from Kobe University challenges the assumptions underpinning this technique. The team tackled a situation where the 120-degree pattern wasn’t a reliable indicator of special properties. Researchers found that alignment dictates the threefold component, with applicability across a wide class of materials. “I was drawn to the intriguing nature of this exception, so I wanted to tackle the problem,” Fuseya said, detailing how a higher-order analysis of a 70-year-old classical theory revealed the possibility of threefold symmetry even in non-triangular crystals. “The point is alignment: The crystal-probe orientation dictates the threefold component, with applicability across a wide class of materials,” the researchers write.
In solid-state physics, beautiful laws underpinned by symmetry hold true. For example, in a crystal with the symmetry of a square, that same symmetry is usually reflected in its physical response. However, the problem we tackled this time is a bit different,” says Kobe University quantum solid state physicist FUSEYA Yuki.
Crystal Alignment Dictates Voltage Patterns in Materials
Kobe University physicists are refining how materials scientists interpret a common diagnostic tool used to identify materials with unique quantum properties. Researchers analyze the voltage pattern as the magnetic field rotates to infer material properties. However, the Kobe University group’s calculations reveal that existing models hadn’t accounted for higher-order effects within established classical theory. For example, in a crystal with the symmetry of a square, that same symmetry is usually reflected in its physical response,” explains FUSEYA Yuki, but the team found that alignment dictates the threefold component, a known principle. Their analysis, published in Physical Review B, shows that the 120-degree pattern isn’t necessarily a sign of unusual quantum properties. “What is particularly striking is that the response reflects mirror symmetry rather than much rarer rotational symmetry,” adds YAMADA Akiyoshi, the study’s first author. This means a wider range of materials, when fabricated with a specific crystal orientation, can exhibit this pattern, opening possibilities for more versatile magnetic sensors and devices.
That is, even if the crystal doesn’t have triangular symmetry, its electrical response to a magnetic field may exhibit the same symmetry as a triangle,” explains Fuseya.
Fuseya
