# Rising Stars - Solitons and Superconductors

13 January 2008

Ben Collie

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Now The second in our series of Cambridge University's Rising Stars.  These are young researchers who are telling us all about their research and how it could affect the future of all of us.  This time, it's physicist Ben Collie...

The physics problems we study at school are often to do with the notion of individual objects such as a bouncing tennis ball.  But to understand the world around us fully at some stage we have to consider the properties of continuous regions.  For instance, suppose there's a long strip of ribbon lying flat on your desk.  If you hold one end of the strip flat while you turn the other end upside down then the ribbon gets twisted and its orientation varies continuously along its length.  If you start shaking one end of the strip then tension and speed of motion also vary along the ribbon's length.  To describe properties that vary continuously in this way we use what physicists call a field.

A field is simply a statement of the value of a property at each point in a region.  It can be the temperature at each point in a room, the water velocity at each point in a swimming pool or the orientation at each point along your ribbon.  Fields are especially useful for describing the world at small scales.  At small scales, matter sometimes behaves like a particle and sometimes behaves like a wave.  It turns out that we can bring together these particle or wave behaviours by describing each kind of fundamental particle in terms of a field.  We have an electron field, a photon field and so on.  Each field fills the whole universe and takes a particular value at each point in time and space.  If the field for, say, the electron has ripples or waves moving through it then, roughly speaking, this represents electrons moving through space.

My particular research is to do with things called solitons.  The name comes from the word solitary and the suffix -on which appears in the names of particles like the electron or the photon.  A soliton is a certain type of disturbance in a field and solitons can occur in many different situations.  For an example, think back to the long piece of ribbon on your desk.  It starts off lying flat, you tape one end to the desk then turn the other end upside down and tape that end to the desk too.  The resulting twist is a soliton in the ribbon's orientation field.  It exists because of the different orientations of the two ends of the ribbon.  You can't get rid of it without untaping one of the ends.  An industrial application of solitons is in the development of superconductors: materials which have no electrical resistance at low temperatures.  If you try to apply a magnetic field to a superconductor you find that a network of string-like solitons form inside it and affects the electric field.  Superconductors are used in the construction of powerful electromagnets and might eventually be used to build high performance electric motors.  So understanding solitons could be important for developing the technologies of the future.