Giant Conductivity Enhancement and Superparamagnetism in MnSe Ultrathin Films on SrTiO3 Substrate

Chun-Hao Huang^1*, Chandra Shekar Gantepogu², Peng-Jen Chen⁴, Ting-Hsuan Wu², Wei-Rein Liu³, Kung-Hsuan Lin¹, Chi-Liang Chen³, Ting-Kuo Lee⁵, Ming-Jye Wang⁶, Maw-Kuen Wu¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan
³Physics Division, National Center for Theoretical Sciences, Hsinchu, Taiwan
⁴National Synchrotron Radiation Research Center, Hsinchu, Taiwan
⁵Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
⁶Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan

* Presenter:Chun-Hao Huang, email:k147m258s369h@gmail.com

The observation of superconductivity in MnSe at 20 GPa motivates us to investigate whether superconductivity can be induced in MnSe at ambient condition. Strain induced structural change of ultrathin film could be one route to the emergence of superconductivity. In this report, we present the physical property of MnSe ultrathin films, which become tetragonal (stretched ab-plane and shortened c-axis) on (001) SrTiO3 substrate, prepared by pulsed laser deposition method. The physical properties of the tetragonal MnSe ultrathin films exhibit very different characteristics from those of the thick films and polycrystalline samples. The tetragonal MnSe films show superparamagnetism with giant conductivity enhancement. The optical absorption data indicates that the electron transition through the indirect bandgap to the conduction band is significantly enhanced in tetragonal MnSe. Furthermore, the X-ray Mn L-edge absorption results also reveal the increase of unoccupied states at the top of valance band. Theoretical study suggests that charge transfer from the substrate plays an important role on the giant conductivity enhancement and the emergence of superparamagnetism.

Keywords: MnSe, epitaxial, x-ray absorption spectroscopy, charge transfer