Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehen...Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehensive characterization of the electronic state reconstruction in the nematic phase is thus crucial.However,most experiments focus only on the reconstruction of band dispersions.Another important characteristic of electronic state,the spectral weight,has not been studied in details so far.Here,we studied the spectral weight transfer in the nematic phase of FeSe0.9S0.1 using angle-resolved photoemission spectroscopy and in-situ detwinning technique.There are two elliptical electron pockets overlapping with each other orthogonally at the Brillouin zone corner.We found that,upon cooling,one electron pocket loses spectral weight and fades away,while the other electron pocket gains spectral weight and becomes pronounced.Our results show that the symmetry breaking of the electronic state is manifested by not only the anisotropic band dispersion but also the band-selective modulation of the spectral weight.Our observation completes our understanding of the nematic electronic state,and put strong constraints on the theoretical models.It further provides crucial clues to understand the gap anisotropy and orbital-selective pairing in iron-selenide superconductors.展开更多
Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been ...Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11888101,91421107,and 11574004)the National Key Research and Development Program of China(Grant Nos.2016YFA0301003 and 2018YFA0305602).
文摘Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehensive characterization of the electronic state reconstruction in the nematic phase is thus crucial.However,most experiments focus only on the reconstruction of band dispersions.Another important characteristic of electronic state,the spectral weight,has not been studied in details so far.Here,we studied the spectral weight transfer in the nematic phase of FeSe0.9S0.1 using angle-resolved photoemission spectroscopy and in-situ detwinning technique.There are two elliptical electron pockets overlapping with each other orthogonally at the Brillouin zone corner.We found that,upon cooling,one electron pocket loses spectral weight and fades away,while the other electron pocket gains spectral weight and becomes pronounced.Our results show that the symmetry breaking of the electronic state is manifested by not only the anisotropic band dispersion but also the band-selective modulation of the spectral weight.Our observation completes our understanding of the nematic electronic state,and put strong constraints on the theoretical models.It further provides crucial clues to understand the gap anisotropy and orbital-selective pairing in iron-selenide superconductors.
基金the National Natural Science Foundation of China(Grant Nos.11504312,11775102,and 11805088)the National Basic Research Program of China(Grant No.2015CB921103)+2 种基金China Postdoctoral Science Foundation(Grant No.2018M641477)Guangdong Provincial Department of Science and Technology,China(Grant No.2018A0303100013)the Fundamental Research Funds for the Central Universities,China(Lanzhou University,Grant No.lzujbky-2018-19).
文摘Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.