Giant anomalous Nernst effect and quantum-critical scaling in a ferromagnetic semimetal

• Published in: Nature physics Vol. 14; no. 11; pp. 1119 - 1124
• Main Authors: Sakai, Akito, Mizuta, Yo Pierre, Nugroho, Agustinus Agung, Sihombing, Rombang, Koretsune, Takashi, Suzuki, Michi-To, Takemori, Nayuta, Ishii, Rieko, Nishio-Hamane, Daisuke, Arita, Ryotaro, Goswami, Pallab, Nakatsuji, Satoru
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2018; Nature Publishing Group
• Subjects: 639/301/1005/1007; 639/766/119/2792/4128; 639/766/119/2795; 639/766/119/995; 639/766/119/997; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Conduction; Curvature; Ferromagnetism; Letter; Mathematical analysis; Mathematical and Computational Physics; Molecular; Nernst-Ettingshausen effect; Optical and Plasma Physics; Physics; Physics and Astronomy; Scaling; Temperature; Temperature dependence; Temperature gradients; Theoretical; Thermoelectricity
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-018-0225-6

In conducting ferromagnets, an anomalous Nernst effect—the generation of an electric voltage perpendicular to both the magnetization and an applied temperature gradient—can be driven by the nontrivial geometric structure, or Berry curvature, of the wavefunction of the electrons 1 , 2 . Here, we report the observation of a giant anomalous Nernst effect at room temperature in the full-Heusler ferromagnet Co 2 MnGa, an order of magnitude larger than the previous maximum value reported for a magnetic conductor 3 , 4 . Our numerical and analytical calculations indicate that the proximity to a quantum Lifshitz transition between type-I and type-II magnetic Weyl fermions 5 – 7 is responsible for the observed – T log( T ) behaviour, with T denoting the temperature, and the enhanced value of the transverse thermoelectric conductivity. The temperature dependence of the thermoelectric response in experiments and numerical calculations can be understood in terms of a quantum critical-scaling function predicted by the low-energy effective theory over more than a decade of temperatures. Moreover, the observation of an unsaturated positive longitudinal magnetoconductance, or chiral anomaly 8 – 10 , also provides evidence for the existence of Weyl fermions 11 , 12 in Co 2 MnGa. A magnetic field and temperature gradient produce a large electric potential in a ferromagnet, indicating the possible presence of Weyl points. The specific structure of Weyl points gives the electrons quantum-critical properties.