Peking University Finds eMChA in 2M-WS2 Flakes

Researchers from Peking University and collaborating institutions across China have observed an unexpected phenomenon in atomically thin flakes of 2M-WS2: anomalous chiral transport, even though the material possesses a symmetry that should preclude such behavior. This electronic magnetochiral anisotropy, or eMChA, was detected via second-harmonic generation under a magnetic field. The team reports that eMChA becomes significant around a crossover temperature of 25 Kelvin, coinciding with a transition from Fermi liquid (FL) to strange metal (SM) behavior within the material. These observations, detailed in a recent publication, suggest a direct link between nonlinear electrical responses, the Nernst effect, and this metal transition, potentially offering new insights into unconventional superconductivity.

Electronic Magnetochiral Anisotropy in Centrosymmetric 2M-WS2 Flakes

A material previously thought to adhere to strict symmetry rules is exhibiting unexpected electrical behavior, challenging established understandings of electron flow. Researchers collaborating across ten institutions in China, including Peking University and Shanghai Jiao Tong University, have detected a phenomenon called electronic magnetochiral anisotropy, or eMChA, within flakes of 2M-WS2, a material known to be centrosymmetric. This observation is surprising because centrosymmetry typically precludes the kind of chiral transport now being observed. Theoretical analysis suggests that the contribution from the orbital magnetic moment at the Fermi surface increases during the Fermi liquid (FL) to strange metal (SM) transition. First-principles calculations point to a “thick-layer-sliding mechanism with minimal energy gain” as a potential source of this unusual quantum geometry within the 2M-WS2 structure. The interplay between eMChA, the Nernst response, and the FL-SM transition positions 2M-WS2 as a unique platform for investigating chiral transport and potentially informing the complexities of unconventional high-temperature superconductivity, a scientific issue that has remained unresolved for decades.

Fermi Liquid to Strange Metal Transition at ~25K

Researchers from Peking University and collaborating institutions across China, including Shanghai Jiao Tong University, report that eMChA becomes significant around the crossover temperature of approximately 25 Kelvin from the Fermi liquid (FL) to strange metal (SM) state. This observation is particularly noteworthy because the 2M-WS2 flakes exhibited this behavior despite being centrosymmetric, a property typically associated with a lack of the asymmetry needed for this type of electrical behavior. The researchers connected this phenomenon to a “direct correspondence between the nonlinear response, Nernst response, and FL-SM transition in 2M-WS2”, suggesting a unified origin for these seemingly disparate effects. Theoretical work points to the importance of nontrivial quantum geometry in driving both the eMChA and Nernst effects, with the contribution from orbital magnetic moments increasing as the material enters the strange metal phase.

The team reports observing electronic magnetochiral anisotropy, or eMChA, in flakes of this material, a phenomenon typically requiring broken symmetry, yet appearing in intrinsically centrosymmetric 2M-WS2. This observation, detected via second-harmonic generation under an out-of-plane magnetic field, challenges conventional understandings of chiral transport and may lead to further research in the field.