This study focuses on one of the most intriguing electrical phenomena in modern physics: the topological Hall effect (THE). In the ordinary Hall Effect, a magnetic field simply pushes the flowing electrons sideways; however, the deflection is caused by a hidden internal force. This effect occurs when electrons encounter a complex swirling magnetic texture—often a tiny, vortex-like structure known as a skyrmion. Essentially, these exotic magnetic swirls act as a “fictitious magnetic field” that dictates the electron path, an effect rooted in a quantum concept called the Berry curvature. Therefore, detecting the THE is a crucial signpost for the existence of these nontrivial, potentially useful magnetic configurations.

We successfully observed a clear signature of the THE within the magnetic state of PrSb₂. This finding is highly significant because this compound is qualitatively distinct from previously reported THE-hosting materials. The magnetism of PrSb₂ involves orbital angular momentum, unlike the simpler “spin-only” systems studies in the past.

What makes the discovery of PrSb₂ even more remarkable is its crucial connection to another fundamental state of matter: the charge-density wave (CDW). A CDW is a static periodic distortion of the crystal lattice and electron density of the material. At ambient pressure, PrSb₂ is an antiferromagnet below 5 K, but exhibits a CDW transition at a much higher temperature of 100 K. The real breakthrough came from a pressure study. As the external pressure was systematically increased, the CDW transition was suppressed. At a critical pressure of approximately 1.0 GPa, where the CDW was almost eliminated, the topological Hall effect vanished dramatically. This strong correlation is at the core of the discovery. It suggests that the CDW state is a crucial prerequisite for the formation of exotic swirling magnetic textures (such as skyrmions) that cause the THE.

Despite this breakthrough, the specific magnetic and crystal structures that host the THE are currently unclear, highlighting the need for further detailed structural studies to fully determine them. Nevertheless, this research opens a promising new avenue in the search for new materials with nontrivial magnetic structures.

(Written by S. Araki on behalf of all the authors)

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