`A completely new type of Bloch-Wilson nonmetal-to-metal transition'
F.Yonezawa, H.Ohtani and T.Yamaguchi
Physica B 296289 (2001).
The purpose of this work is to review our previous work about
the mechanism for the nonmetal-to-metal (NM-to-M) transition
on volume expansion in supercritical Se.
In the attempt of solving this problem,
we discover a completely new type of Bloch-Wilson NM-to-M
transition, which we name as ``Type II.''
On volume expansion, the traditional type of Bloch-Wilson transition,
which we denote as Type I,
takes place from metal to nonmetal (M-to-NM) in materials
previously studied such as liquid Hg.
This M-to-NM transition is brought about by the band open-up
because of the band narrowing accompanying the increase of volume.
In liquid Se, Se chains are fragmented into small chains
of size 10 when volume is expanded.
The antibonding band associated with the weakened bonding
between chain ends moves down and eventually the band overlap occurs,
giving rise to NM-to-M transition.
The lowering of the antibonding band is caused by the decrease
of the energy splitting between the bonding and antibonding level
according to the increase of bond length.
We also point out that the electronic properties of
the group I{\negthinspace}V elements on the periodic table
are explained in terms of the ``Type II'' scheme.
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2001/07/25