Seminar by John Owen Benton "Condensation of Topological Excitations in Highly Frustrated Ising Models"

Seminar :

• Date: Thursday, 20th April
• Time: 14:00-15:00
• Venue: C016, Lab1
• Speaker: John Owen Benton (Quantum Matter Theory Research Team, RIKEN)
• Title: Condensation of Topological Excitations in Highly Frustrated Ising Models

Condensation of Topological Excitations in Highly Frustrated Ising Models

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.

Imbuing Ising models with frustrated interactions can suppress ordering, and replace it with something arguably richer. 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 trivial 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. This includes the case of spin ice and of ``kagome ice'' which is realized by spin ices under an applied field in the (1,1,1) direction. Our approach even succeeds for several cases of frustrated transverse exchange, where controlled numerics is difficult or even impossible. This work suggests a new way forward in understanding the ground state instabilities of highly frustrated quantum magnets.

Hosted by Theory of Quantum Matter Unit

Contact: shiho.saito@oist.jp