It was recalled that an elastic softening at low temperatures had been observed in Si by using ultrasonic measurements. By assuming that an intrinsic defect of vacancy caused this softening, which was suggested by experiment, the effects of a monovacancy upon the elastic properties were theoretically studied. The primary concern here was to survey the existence of a low-energy excitation, which would be commonly expected for such an abnormal behavior. Although the static ground-state of monovacancy was stiff owing to the strong Jahn-Teller distortion, it was found that a low-energy excitation really existed in the motion of the neighboring Si atoms surrounding the vacancy.

On the Elastic Softening due to a Vacancy in Si. J.Ishisada, K.Shirai, H.Dekura, H.Katayama-Yoshida: Journal of Physics - Conference Series, 2007, 92[1], 012063 (4pp)