The distortion of MnSe₆ octahedron enhanced the conductivity and quenched the magnetic anomaly in epitaxial MnSe film.
Chun-Hao Huang1,2*, Chandu1,4, Ting-Hsuan Wu1, Wei-Hsiang Huang2, Hung-Wei Kuo2, Kung-Hsuan Lin1, Chi-Liang Chen2, Ming-Jye Wang3, Maw-Kuen Wu1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
2Absorption Group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
3Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
4Department of Physics, National Taiwan University, Taipei, Taiwan
* Presenter:Chun-Hao Huang,
The observation of superconductivity in MnSe at high pressure motivates us to investigate whether superconductivity is induced in MnSe at ambient condition. In this report, we have grown a series of MnSe films with different thickness by pulsed laser deposition (PLD) on SrTiO3 (STO) substrate, and study the physics properties in MnSe. Although no superconductivity is observed in this system, both the transport and magnetic properties in film type apparently exhibit different behavior with polycrystalline type. Especially, the resistivity of MnSe film is also apparently gradually conductive accompany with the decrease of thickness at room temperature. Moreover, the typical anti-ferromagnetic anomaly in MnSe is absent in 30 nm film. The lattice structure of MnSe films is determined by four-circle diffractometer and indicating the appearance of distortion of MnSe6 octahedron in 30 nm film. The electric property which is varied by epitaxial strain are further investigated by optical transmission spectra (OPS), and indicating both the indirect gap and direct gap of 30 nm MnSe are smaller than that in 740 nm MnSe. Additionally, the Mn valence and unoccupied states in both film and polycrystalline type MnSe were determined by x-ray absorption spectroscopy (XAS). The results indicate the valence of polycrystalline type is close to 2+, but that in film type is close to Mn foil. Furthermore, the unoccupied states in film type is systematically raised as the decrease of thickness, and these are apparently larger than bulk type. Therefore, the key of the promotion of conductivity and the quenched magnetic anomaly in MnSe film is that the STO provides the tensile lattice strain to distort the MnSe6 octahedral structure.

Keywords: MnSe, four-circle diffractometer, susceptibility and resistivity, optical transmission spectra , x-ray absorption spectroscopy