Project/Area Number  03640334 
Research Category 
GrantinAid for Scientific Research (C).

Research Field 
物性一般（含極低温･固体物性に対する理論）

Research Institution  Osaka University 
Principal Investigator 
KAWAMURA Hikaru Osaka University, College of General Education, Associate Professor, 教養部, 助教授 (30153018)

CoInvestigator(Kenkyūbuntansha) 
OHTSUKI Tomi Osaka University, College of General Education, Assistant, 教養部, 助手 (50201976)
SAITOH Motohiko Osaka University, College of General Education, Professor, 教養部, 教授 (80012441)

Project Fiscal Year 
1991 – 1992

Project Status 
Completed(Fiscal Year 1992)

Budget Amount *help 
¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1992 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1991 : ¥1,000,000 (Direct Cost : ¥1,000,000)

Keywords  topological transitions / triangular lattice antiferromagnets / Monte Carlo simulations / chirality / twodimensional electron systems / Stark ladder / Wigner crystal / Anderson transitions / トポロジカル相転移 / 3角格子反強磁性体 / モンテカルロ法 / カイラリティ / 2次元電子系 / シュタルク・ラダー / ウィグナー結晶 / アンダーソン転移 / 量子融解 / 2次元素 / 繰り込み群 / フラストレション / モンテカルロシミュレション / 電子ーリプロン相互作用 / シュタルク・ラダ / アンダソン転移 
Research Abstract 
Topological phase transitions of twodimensional systems with vortex excitations are analyzed. As a new type of order parameter of such topological transitions, a vorticity modulus is introduced and its behavior is studied by means of a Monte Carlo sinulation combined with an appropriate type of boundary conditions. TwoDimensional XY (plane rotator) model, triangularlattice Heisenberg antiferromagnet and ferromagnetic Heisenberg model are studied and the results are analyzed based on a finitesize scaling theory. In the case of the XY model, the results support a theory proposed by KosterlitzThonless, while in case of triangular antiferromagnets, the results support the occurrence of a finitetemperature topological transition driven by Z_2 vortices as suggested by Kawamura and Miyashita. Critical properties of triangularlattice antiferromagnets are studied near two dimensions on the basis of a field theoretic nonlinear sigma model and the renormalizationgroup epsilon=d2 expansion. Critical properties of XY and Heisenberg antiferromagnets on a threedimensional stackedtriangular lattice are also studied directly by extensive Monte Carlo simulations. The estimated exponents and the amplitude ratio are in good agreement with the experimental results. Electronripplon interactions in a twodimensional electron system on liquid helium surface are studied. With a twodimensional hyperlattice in mind, energy spectrum of tightbinding models under strong magnetic and electric fields are studied. Transport properties of layered electronic systems under strong magnetic fields are studied.
