1,691 research outputs found
Superlattice formation lifting degeneracy protected by non-symmorphic symmetry through a metal-insulator transition in RuAs
The single crystal of RuAs obtained by Bi-flux method shows obvious
successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The
X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of
the original unit cell below T_MI2, accompanied by a change of the crystal
system from the orthorhombic structure to the monoclinic one. Simple
dimerization of the Ru ions is nor seen in the ground state. The multiple As
sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate
the formation of the superlattice in the ground state, which is clarified to be
nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by
the metal-insulator transition is accompanied by strong critical fluctuations
of some degrees of freedom. Using the structural parameters in the insulating
state, the first principle calculation reproduces successfully the reasonable
size of nuclear quadrupole frequencies for the multiple As sites, ensuring the
high validity of the structural parameters. The calculation also gives a
remarkable suppression in the density of states (DOS) near the Fermi level,
although the gap opening is insufficient. A coupled modulation of the
calculated Ru d electron numbers and the crystal structure proposes a formation
of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows
that a lifting of degeneracy protected by the non-symmorphic symmetry through
the superlattice formation is a key ingredient for the metal-insulator
transition in RuAs.Comment: 10 pages, 10 figure
Effects of prolonged weak anodal direct current on electrocorticogram in awake rabbit.
The effects of prolonged weak anodal direct current (DC) on the electrocorticogram (ECoG) were investigated in awake rabbits. When the current (20-40 microA) was applied to the motor region of the cerebral cortex, seizure activity in the ECoG appeared from the frontal cortex. Repeated application of the DC decreased the threshold current for producing the seizure activity. Diazepam significantly elevated the threshold of the seizure activity. In contrast to the marked changes in the ECoG, no behavioral changes were observed during or after the application of weak anodal DC. The changes in the ECoG are discussed in relation to the intensity and duration of the DC.</p
進行波型半導体分布結合ガイド光変調器に関する研究
University of Tokyo (東京大学
芳香族窒素配位基を有する三脚型四座配位子を含む二核銅錯体による酸素分子の結合と活性化の研究
取得学位:博士(理学),学位授与番号:博甲第457号,学位授与年月日:平成14年3月22日,学位授与年:200
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