Masaaki Shimozawa

We have performed careful measurements of nonlinear transverse conductivity (NLTC) at zero field in the intermetallic compound HoAgGe with two distinct magnetic toroidal (MT) structures. Below 7 K (MT1 phase), the NLTC signal becomes observable and significantly increases with decreasing temperature, whereas between 7 and 11.6 K (MT2 phase), it remains nearly zero. However, this result is incompatible with the previous research, which assigned the former and latter MT phases as antiferro- and ferro-MT structures, respectively. This discrepancy stems from an inappropriate assignment of MT structures in prior studies. Our analysis, based on multipole theory, redefines the MT1 and MT2 phases as ferri- and antiferro-MT structures, respectively, providing a coherent framework to explain the observed NLTC in HoAgGe. These findings not only establish NLTC as a robust diagnostic tool for identifying MT metals but also highlight its potential for exploring phenomena driven by the antiferroic interactions of MT dipoles.

The manipulation of the valley degree of freedom can boost the technological development of novel functional devices based on valleytronics. The current mainstream platform for valleytronics is to produce a monolayer with inversion asymmetry, in which the strain-band engineering through the substrates can serve to improve the performance of valley-based devices. However, pinpointing the effective role of strain is inevitable for the precise design of the desired valley structure. Here, we demonstrate the charge transport under continuously controllable external strain for bulk bismuth crystals with three equivalent electron valleys and one hole valley. The strain response of resistance, namely elastoresistance, exhibits evolutions in both antisymmetric and symmetric channels with decreasing temperature. The elastoresistance behaviors mainly reflect the significant changes in valley density depending on the symmetry of induced strain, evidenced by our strain-dependent quantum oscillation measurements and first-principles band calculations under strain. These facts suggest the successful tuning and evaluation of the valley populations through strain-dependent charge valley transport. Published by the American Physical Society 2024