Quantum phase transitions: Tunneling spectroscopy and the energy gap

1. Craig J. Hawker, University of California-Santa Barbara, DMR 0520415 Quantum phase transitions: Tunneling spectroscopy and the energy gap at complex oxide interfaces. Tunneling spectroscopy of the gap / pseudo gap in Mott materials Ceramic LaNiO3 4.2 K 3nm LaNiO3, 1.8 K The energy gap is a key feature of materials that undergo a Mott metal-insulator transition driven by strong electron-electron interactions. The resistance seen by electrons that tunnel into a Mott insulator measures the energy gap in the insulating phase. Equally important, a “pseudo” gap, a precursor of a “real” gap, appears as electrons tunnel into a Mott metal. The evolution of a “pseudo” gap into a “real” gap, at the quantum critical point, is an important experimental test of theories of the metal-insulator transition at complex oxideinterfaces. “Pseudo” gap seen by tunneling conductance through a 4 unit cell SrTiO3 barrier into epitaxial LaNiO3, an incipient Mott insulator.