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The electronic structures of M-doped SnTe (M = Mg, Mn, Cd, and Hg) are investigated by using first-principles calculations including spin-orbit coupling. It is found that Sn vacancy plays an important role in the band engineering of SnTe, showing a different property from its related compound PbTe. The enlarged band gap and reduced energy separation between two valence bands are in good agreement with experimental measurements. Both of the two band modifications lead to the increase of Seebeck coefficients, which is explicitly confirmed by the followed Boltzmann transport calculations. The calculated Seebeck coefficients for Mn-doped SnTe agree well with the experimental data in a broad range of carrier concentration. Owing to the improved Seebeck coefficients, Mn- and Cd-doped SnTe exhibit promising thermoelectric properties with ZT = 1.32 and 1.65 at around 800 K, respectively.

We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca3Ru2O7. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.