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Direct Observation of Dynamics of Electrons Starting to Move Upon Application of Ultrahigh Pressure -Using high-brilliance infrared rays at SPring-8 (Press Release)

Release Date
10 Dec, 2009
  • BL43IR (Infrared Materials Science)
Kobe University, jointly with The University of Tokyo and Tohoku University, has clarified, using infrared rays, the transition process of ytterbium sulfide (YbS) from an insulator that cannot conduct electricity under atmospheric pressure to an electrically conductive metal, which occurred upon the application of an ultrahigh pressure of 20 GPa, by observing the dynamics of electrons transmitting electricity.

Kobe University

Kobe University, jointly with The University of Tokyo and Tohoku University, has clarified, using infrared rays, the transition process of ytterbium sulfide (YbS) from an insulator that cannot conduct electricity under atmospheric pressure to an electrically conductive metal, which occurred upon the application of an ultrahigh pressure of 20 GPa, by observing the dynamics of electrons transmitting electricity. With the equipment used to generate such a high pressure, only small samples of approximately 0.1 mm in size can be used, and samples must be sealed in a small space to apply the pressure, creating various technological difficulties in experiments using infrared rays. The experiments that led to the above breakthrough were performed using high-brilliance infrared rays produced at SPring-8. The results were published online in Physical Review Letters, an academic journal of the American Physical Society, on 2 December 2009.

Publication:
"Pressure tuning of an ionic insulator into a heavy electron metal: An infrared study of YbS"
M. Matsunami, H. Okamura, A. Ochiai, and T. Nanba
Physical Review Letters, Vol. 103, No. 24 (2009) 237202, published online 2 December 2009

<Figure>

Fig. 1 Schematic of generation of high pressure and infrared spectroscopy setup using diamond anvil cell (DAC)

Fig. 1 Schematic of generation of high pressure and infrared spectroscopy setup using diamond anvil cell (DAC)
An approximately 0.1-mm-sized sample and a pressure-transmitting liquid are sealed in a small space, which consists of a hole in a metal plate enclosed by the two end surfaces of a pair of diamonds. A high pressure of 20-30 GPa can be applied to a sample by applying forces to the diamonds on both sides of the hole. The emission spectra of a sample under high pressure can be measured from the incident and reflective light, as indicated by the red arrows, because diamonds are transparent to light over a wide range of wavelengths including infrared rays.

Fig. 2 Reflectivity of infrared rays by YbS under high pressure

Fig. 2 Reflectivity of infrared rays by YbS under high pressure
The reflectivity of 1 indicates that 100% of light is reflected. "eV" is the unit of energy. The reflectivity is low from atmospheric pressure to 7.8 GPa because YbS acts as an insulator. (The large peak at approximately 0.03 eV is attributable to the vibration of atoms and is frequently observed for other insulators.) However, the reflectivity sharply increases when pressure is increased to higher than 8.3 GPa, as indicated by the bold arrow. This is due to plasma reflection, which is caused after a number of free electrons generated upon the transition of YbS to a metal collectively vibrate. (Plasma reflection is also the origin of the luster of various common metals.)

For more information, please contact:
Associate Prof. Hidekazu OKAMURA (Kobe University)
E-mail: mail