Jammed Spin Liquid

In Plain English

At the heart of this project is the interplay of geometric frustration and disorder in a classical spin system.

You may think of classical spins as arrows or little magnets pointing in a direction in space. As you know from magnets they may want to orient in certain ways with respect to each other, say point in the same or opposite directions.

Geometric frustration is the phenomenon that it may not be possible to "satisfy" all the spins, e.g. if you put spins on a line it is easy to arrange them such that they all point opposite to their neighbours (see image). However, now imagine putting 3 spins in a triangle, you will notice that you can put two spins in the right way, but it's not quite clear what to do with the third. Thus, we observe that the geometric arrangement of the spins (triangle or line) strongly influences the behaviour of the spins.

Disorder here refers to the fact that properties of the system may not be perfect, e.g. the positions of the spins on a grid might be slightly off, or maybe some spins want to point in the same direction and others want to point in opposite directions, or maybe some spins are missing in an otherwise regular arrangement.

Finally, one might wonder how these things relate to each other. From the example on geometric frustration, it is clear that frustration suppresses ordering, the same is true for disorder, and a natural question is if a system still adapts some kind of order in presence of either or both disorder and geometric frustration.

Research

The classical Heisenberg antiferromagnet on the kagome lattice is one of the foundational models of highly frustrated magnetism. At low temperatures it is known to support an exotic phase of matter, a classical spin liquid lacking any local order parameter, but instead being described by emergent gauge fields.

We establish a new type of spin liquid ground state, “a jammed spin liquid”, existing down to zero temperature in the bond-disordered kagome Heisenberg antiferromagnet in a qualitative development beyond the long-studied clean system. This spin liquid establishes conceptual links between the field of frustrated magnetism and the physics of granular media, in particular to the phenomenon of jamming.