New Research


2012/10/01

Disclosed difference between gold and silver other than color

Probing atomic orbital character in solids by polarization-dependent hard x-ray photoemission

Professor Akira Sekiyama, Associate Professor Takayuki Kiss, Assistant Professor Hidenori Fujiwara

  More than 100 years ago, Einstein revealed the principle of photoelectric effects based on the concept of photon (energy quanta), for which he was awarded the Nobel Prize in Physics. In Sekiyama Laboratory in Division of Materials Physics, the electronic structures of materials are investigated by photoemission spectroscopy that utilizes the photoelectric effects, and a cutting-edge methodology of photoemission is developed. Here we show an example of our activity, a new finding for unexpected difference between conventional gold and silver probed by the cutting-edge hard x-ray photoemission spectroscopy.

  Such properties of metals as electric resistivity and magnetism depend predominantly on a character of conduction electrons, which move round inside the metals. There are several atomic orbitals in solids with a different character in a degree of itinerancy or localization, which is a key to understand their electronic properties. However, an experimental technique to simultaneously probe the characters of multiple orbitals with different itinerancy has so far been lacking.

  In Sekiyama Laboratory, a new photoemission technique to reveal the orbital characters of conduction electrons in solids by switching the polarization, which is often used for three-dimensional visualization, of the hard x-ray emitted by the synchrotron radiation has successfully been developed. By applying this technique, it has been found that a rather localized orbitals contribute prominently to the conduction electrons in gold while the conduction electrons in silver are free-electron-like, which is rather contrary to the common expectation for the conduction-electron character in gold and silver. On the other hand, our finding might be related to well-known facts that gold is more stable than silver and that the electric resistivity is lower for silver than for gold. This method will be powerful to reveal the conduction-electron character in many functional materials.

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