Nonvolatile isomorphous valence transitions in SmTe films

• The rapidly developing field of optoelectronic devices requires a mechanism that can produce huge contrasts in electrical and optical properties. Yuji Sutou and Shogo Hatayama of Tohoku University in Japan demonstrated that there is a mixed Sm valence state in a non-equilibrium state in SmTe films under ambient conditions.

  
  

  The compressive stress induced during sputter deposition contributes to the stabilization of these mixed valence states in the deposited film. Furthermore, annealing can adjust the balance of Sm3+ and Sm2+ fractions. After the valence transition (VT), we observe significant differences in ρ (over 105) and Eg (about 1.45 eV) of the as-deposited (low ρ) and 440°C annealed (high ρ) films, although the crystal structure is almost no change. Furthermore, mixed valence states can be manipulated within nanoscale devices by applying Joule heating induced by electrical pulses.

  
  

  These findings propose a paradigm for ESC via VT, capable of achieving a wide range of material properties, such as amorphous-to-crystalline transitions, without changing atomic species or drastic atomic rearrangements.

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• Shogo Hatayama*, Shunsuke Mori, Yuta Saito, Paul J. Fons, Yi Shuang, and Yuji Sutou*, Nonvolatile Isomorphic Valence Transition in SmTe Films. ACS Nano 2024

  
  

  DOI: 10.1021/acsnano.3c07960

  
  

  https://doi.org/10.1021/acsnano.3c07960