Paramagnon drag yields a high thermoelectric figure of merit in Li-doped MnTe*

MnTe is an antiferromagnetic semiconductor with a Neel temperature of 307 K. In the antiferromagnet phase, the magnon-electron interaction gives rise to a magnon-drag contribution to thermopower. Surprisingly this magnon-drag thermopower extends to the paramagnetic phase. Experimental results provide evidence for the effect of locally ordered thermal fluctuations of magnetization with finite lifetime (paramagnons). When the lifetime of the paramagnons is longer than the electron-paramagnon scattering time, the paramagnons can effectively push the electrons and contributes to thermoelectric power. By analyzing the measured thermopower, resistivity, Hall coefficient, specific heat and magnetization, a quantitative explanation is given for thermopower of both the AFM and PM regime based upon the hydrodynamic theory [1]. As a result, the ZT of the best sample exceeds 1 at 950 K.