投稿者 : taku 投稿日時： 2010-09-13 12:19:54 (8835 ヒット)
An electron is a magnet. However, the magnetic moment of the electron can take only the two states, up and down, which is in contrast to the real-life magnet which can have any direction. This degree of freedom, up and down states, is called "spin". When the two spins interact with each other antiferromagnetically, surprisingly they couple, and disappear (formation of singlet). In strongly frustrated lattice as kagome lattice, this coupling cannot be formed trivially; up spin cannot select which down spin to couple... Consequently, the singlet state starts to move around the lattice; the resonating-valence-bond state. When a weak breaking of the complete frustration is introduced, the singlet solidifies, resulting in the valence-bond-solid state. Of course, the spins hide themselves by forming singlet pairs, so they are not easy to be seen experimentally. We, a team from ISSP, Tokyo Tech. and Tokyo Univ. of Science, uses neutron scattering to "see" the hidden state by exciting the singlet ground state into triplet excited state. In this experiment, we confirm the pinwheel VBS state in the model kagome antiferromagnet Rb2Cu3SnF12. This result is published in Nature Physics on 2010/09/12. Detail in Japanese can be found elsewhere.
投稿者 : taku 投稿日時： 2010-01-25 23:44:35 (6678 ヒット)
X-ray scattering cross section of an atom is given by the number of its elections. Therefore, it is not easy to see light elements, which are indeed practically very important since they can move in a certain class of solids which makes them useful for the fuel cell or oxygen transport ceramic membrane. Neutrons scattering cross section does not depend on the number of elections, and indeed neutrons can be reasonably scattered by light elements. Therefore, we can investigate the position and dynamics of light elements in solids. Using this unique feature, a group comprising researchers from Tokyo Tech. and Kyushu Univ. has succeeded in visualizing the oxygen conduction path in the praseodymium nickel oxide (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+d. This material conducts both the ions and holes at the same time, and is hoped to be applicable to the solid oxide fuel cell and oxygen transport ceramic membrane. This work has been carried out using the IMR's HERMES neutron diffractometer, installed at the JRR-3 research reactor, through the ISSP-NSL user program, and will be published in J. Am. Phys. Soc., a leading journal in the field of chemistry and materials science. For details, please visit press release at Tokyo Tech.