The temperature dependence of anomalous Lorenz number: Mn₃Sn, conventional ferromagnets: Ni, Ni_0.97Cu_0.03, Fe.

(Phys. Rev. Lett. 119, 056601(2017))

Background

The ordinary Hall effect, the transverse electric field generated by a longitudinal charge current in presence of a magnetic field, is caused by the Lorentz force exerted by magnetic field on charge carriers. In ferromagnetic solids, there is an additional component to this response (known as extraordinary or anomalous), thought to arise as a result of a sizeable magnetization. And thus Anomalous Hall effect is not usually seen in antiferromagnets in zero field. According to recent theoretical calculations, the Anomalous Hall effect(AHE) can be observed in some special noncollinear antiferromagnetic materials, such as Mn₃Ir. Recently, Nakasutji et al. and Nayak et al. revealed a large AHE in Mn₃Sn and Mn₃Ge which are noncollinear antiferromagnets at room temperature.

What we discover?

Therefore, we presented a study of electric, thermoelectric and thermal response in noncollinear antiferrmagnet Mn₃Sn, such as Anomalous Hall Effect(AHE), Anomalous Nernst effect(ANE) and Anomalous Righi-Leduc effect(ARLE). Our study found that the thermal and electrical Hall conductivities respect the Wiedemann-Franz law, implying that the transverse currents induced by Berry curvature are carried by Fermi surface quasi-particles. And in contrast to conventional ferromagnets Ni, Ni_0.97Cu_0.03 and Fe, the anomalous Lorenz number remains close to the Sommerfeld number over the whole temperature range of study, excluding any contribution by inelastic scattering and pointing to Berry curvature as the unique source of AHE. And we also found that the anomalous off-diagonal thermo-electric and Hall conductivities are strongly temperature dependent and their ratio is close to k_B/e.

Why is this important?

The observation of the Wiedemann-Franz Law has an important implication for our understanding of origin of the anomalous Hall effect.The result confirms that, as Haldane suggested in a 2004 PRL paper, the Hall current generated by Berry curvature is carried by Fermi surface quasi-particles and not by the whole Fermi sea. The ratio ofanomalous off-diagonal thermo-electric and Hall conductivitiesshould motivate theorists to elaborate on first-principle calculations of band structure and Berry curvature in this family as well as others.

Why did they need WHMFC?

In a magnetic field induces all off-diagonal term of transport tensors including AHE, ANE and ARLE which are the main methods used in this research.

Who did the research?

Xiaokang Li¹, Liangcai Xu¹, Linchao Ding¹, Jinhua Wang¹, Mingsong Shen¹, Xiufang Lu¹, Zengwei Zhu¹, and Kamran Behnia^1,2

¹Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China

²Laboratoire de Physique Et d’Etude des Matériaux (UPMC-CNRS), ESPCI Paris, PSL Research University, 75005 Paris, France

Funding:

This study was supported by the 1000 Youth Talents Plan,the National Science Foundation of China (Grant No. 11574097),the National Key Research and Development Program of China(Grant No.2016YFA0401704) and China High-end foreign expert programme.

P. S.

Zengwei Zhu returned to the Center in 2014, he is now in charge of the Electrical Transport Experimental Station (also High Pressure Station) in Wuhan National High Magnetic Field Center. And his researches mainly focus electric and thermal transport on semimetals, superconductors and strongly correlated electron systems etc. In the last three years, his team has three high-level papers published in the top-notch journals: Physical Review Letters (2) and Nature Communications (1). One among them published in the May 2015,titled“Quantum oscillations, Thermoelectric Coefficients and the Fermi Surface of Semi-metallic WTe2”is an ESI highly cited paper.