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The half-filled Landau level: the case for Dirac composite fermions


In an external magnetic field, the energy of an electron in a two-dimensional system takes discrete values, called Landau levels. At high enough fields, all electrons in a solid can fit in the lowest Landau level. If exactly half of that level is filled with electrons, standard theory predicts that a special fermion liquid phase will form that makes a distinction between the filled and empty states (particles and holes). A recent conjecture, in contrast, predicted a liquid consisting of massless Dirac particles that respects the symmetry between particles and holes. A collaboration led by researchers at Station Q Santa Barbara and the Institute for Quantum Information and Matter at Caltech used sophisticated numerical methods to provide strong evidence for this conjecture. The article appeared recently in Science.

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