セミナー情報

第55回 原研・兵県大合同コロキウム

日時: 平成21年3月10日(火) 13:00〜
Date and time: 10th Mar. (Tue.) 13:00〜
場所: SPring-8, 萌光館
Place: SPring-8, "HOUKOUKAN" seminar room
題目: 膨張アルカリ金属の「電荷秩序転移」
Title: "Charge-ordering transition" in an expanded alkali metal
講演者: 前橋 英明 氏 (東大物性研)
Speaker: Dr. Hideaki Maebashi (Institute for Solid State Physics, University of Tokyo)
Abstract:

A liquid alkali metal is a simple system composed of monovalent ions and valence electrons, but it is a useful system to study the important physics of the strong exchange-correlation effect due to the long-range Coulomb interaction, because the electron density is rather low. With further decreasing density by volume expansion, we can realize even more interesting situation in which the metal-non-metal transition occurs concomitantly with the liquid-gas phase transition: In the density-temperature phase diagram, the metal-non-metal transition curve above the liquid-gas critical point is transformed to phase separation of the liquid metallic state and the gaseous non-metallic one with decreasing temperature.

In this talk, we shall argue that the metal-non-metal transition thus related to the phase separation in an expanded alkali metal is a "charge-ordering transition" caused by anomalous electronic density fluctuations occurring at some finite wave vector Q; since |Q| is smaller than the diameter of the Fermi surface, this transition necessarily impedes the electronic conduction. We observe that this type of charge-ordering transition is a rather universal phenomenon originating from the negative compressibility characteristic of the low-density electron gas combined with the q=0 singularity in the Fourier transform of the long-range Coulomb interaction. This observation suggests that some phase separation may also be expected in the vicinity of the charge-ordering transition in other systems with the long-range Coulomb interaction, such as organic conductors.