セミナー案内
- 日時 ： 7月25日（水） 午後１時３０分～
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場所 ：理学部Ｆ棟５階 理論物質学セミナー室（Ｆ５２４）
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講演者 ：Owen Benton 氏（理研）
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タイトル：「Condensation of Topological Excitations in Highly Frustrated
Quantum Ising Models」
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概要 ：
Ising models have been central to the study of
magnetism for nearly 100 years. They have provided deep
insights into magnetic order and the theory of phase transitions.
When Ising models have frustrated interactions, even richer
scenarios may arise. This is exemplified by the spin ices
- Ising-like magnets on the pyrochlore lattice. The simplest
model of spin ice predicts no magnetic order at any temperature
and yet the low temperature physics is far from that of a
simple paramagnet. The low energy states possess subtle
topological properties and "magnetic monopole” excitations.
The monopoles are examples of topological excitations- no
local process can create or destroy a single monopole.
There are several quantum magnets related to the spin ices
but possessing transverse terms in their spin Hamiltonian which
generate monopole dynamics- so-called ``quantum spin ices''.
For sufficiently strong transverse terms the monopoles will
condense and destroy the topological order of the ground state
manifold. It is crucial to develop methods to treat this behaviour
if we are to understand the quantum spin ices and other highly
frustrated quantum magnets. In this talk, I will show how the
instability to topological defect condensation may be quantitatively
predicted for a wide class of frustrated Ising models with transverse
perturbations. Our approach can be applied in some cases of
frustrated transverse exchange where Quantum Monte Carlo would
be impossible and also to models with quenched disorder. This work
suggests a new way forward in understanding the ground state
instabilities highly frustrated quantum magnets.
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