The finding of a new class, or flavour, of quantum spin liquids in the mineral kapellasite by an international team made up of researchers from France, Switzerland and the U.K. is attracting excitement as it could herald the discovery of new types of quantum properties.

At
its most fundamental level, classical physics considers liquids as
being made up of atoms, ions or molecules that swirl and flow. In the
quantum world, atomic spins can also be liquid-like. While the spins in
these ‘quantum spin liquids’ are not mobile, the directions that they
point in fluctuate, like a collection of overly excited Weebles. However, if these Weebles
are to model quantum mechanical spins, their movements should be highly
correlated and driven by quantum fluctuations rather than a classical
stimulus, such as being poked by a cat.

Understanding
quantum spin liquids is considered by many to be one of the grand
challenges of physics and has been the focus of intense research for
over 30 years. These exotic states of matter do not follow the classical
rules of our everyday world. Instead, the laws of quantum mechanics
define and control them, and this makes possible new and extraordinary
types of behavior.

Fluctuations
play a key role in quantum spin liquids states, as they not only drive
the spin dynamics, but are able to create excitations that are so
well-defined that they act as particles themselves. They are
correspondingly termed quasi-particles and
their properties are quite different to those of the conventional
building-blocks of matter. Correspondingly, entirely new directions for
physics are being opened up. Possible applications include the emerging
field of quantum information processing,
where information is encoded in spins and quantum laws will govern how
it is processed. It is easy to see why understanding the formation of
quasi-particles and their new physics is captivating modern condensed
matter physics.

One
of the bottle-necks for this research is the scarcity of experimental
materials which can be used to explore and test theoretical predictions.
The finding of a new class, or flavor, of quantum spin liquids in the
mineral kapellasite by an international team made up of researchers from
France, Switzerland and the U.K. is attracting excitement as it could
herald the discovery of new types of quantum properties.

In their article, Phys. Rev. Lett.
109, 037208 (2012), they combine data from a wide range of experimental
techniques with theoretical modelling to characterize its spin
correlations and their dynamics. Their results were very unexpected –
they found that the spins form correlations based on an Archimedean
solid: the highly symmetric cuboctahedron
that is formed when the corners are taken from a cube to create a shape
where every side is the same length. Dr Andrew Wills from the UCL and
the LCN explained that to-date, research in this field had largely been
based around simple models where the spins were only able to point up or
down. Their latest work shows that very sophisticated ‘flavors’ of
quantum spin liquids are possible, and raises the question of what
quasi-particles and extraordinary physics they can host. ‘It is a very
exciting time’, he said, ‘kapellasite has really opened our eyes to the
breadth of the possibilities that are possible in the quantum world.’

As
well as exploring the possibilities of quasi-particles in kapellasite,
the team is working to discover other new types of quantum spin liquid.

Kapellasite: a kagome quantum spin liquid with competing interactions

Source: London Centre for Nanotechnology