Researchers at Nanjing University have identified a new quantum state of matter in a thin carbon material that electrons neither fully two-dimensional nor three-dimensional. The discovery, termed the transdimensional anomalous Hall effect, emerged unexpectedly during experiments in magnetic fields. Lei Wang and his team confirmed the phenomenon after a year of analysis.
Lei Wang at Nanjing University in China and his colleagues were examining a thin material of carbon atoms arranged in rhombuses, aiming to observe efficient electron currents. When immersed in a magnetic field, the electrons displayed unusual behavior, exhibiting a Hall effect under two mutually perpendicular magnetic fields. This allowed looping motions both horizontally and vertically in material just 2 to 5 nanometres thick, which should not support such three-dimensional-like motion in both directions simultaneously. The team named this the transdimensional anomalous Hall effect (TDAHE), a previously unobserved phenomenon not predicted by theory. Wang stated, “TDAHE came about as a complete surprise, a phenomenon never seen in any other material before, nor does any theory predict that.” After initial measurements, they spent about a year verifying the data through follow-up experiments and additional samples, ruling out errors. The state does not blend 2D and 3D traits but represents a distinct regime, according to Wang. Andrea Young at the University of California, Santa Barbara, described the electrons' states as lacking symmetry in three ways, likening it to a “quarter-metal” where symmetries limit electron capabilities. Wang's group plans further studies in other materials using advanced tools like diamond-based magnetic sensors. The findings appear in Nature.
