Metastable phases of matter are well-known, with famous examples including supercooling and superheating of liquids and diamond which is one of the many allotropes of carbon. Metastability is almost exclusively observed in connection with first-order transitions, and is often found in frustrated systems where the energy difference between the states is small.
In a paper published in Physical Review Letters, Notre Dame graduate students Pinaki Das and Cathy Rastovski and former undergraduates Tommy O’Brien and Kim Schlesinger, together with Associate Professor Morten Ring Eskildsen, report their discovery of metastable vortex lattice phases in superconducting MgB2. Surprisingly, the metastable phases are associated with a second-order phase transition and cannot be understood based on the vortex-vortex interaction. Instead it is speculated that the metastable phases are due to jamming, similar to what is found in connection with granular materials.
The results were obtained by small-angle neutron scattering experiments carried out at Institut Laue-Langevin, France, and in the US at Oak Ridge National Laboratory and at the National Institute for Science and Technology. The work is supported by the US DOE Office of Basic Energy Science Grant DE-FG02-10ER46783.