Physics

Interface Pseudogap

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Science  29 Nov 2013:
Vol. 342, Issue 6162, pp. 1021
DOI: 10.1126/science.342.6162.1021-c
CREDIT: C. RICHTER ET AL., NATURE 502, 7472 (24 OCTOBER 2013) © NATURE PUBLISHING GROUP

The superconductivity of copper oxide compounds, which in some cases can persist to temperatures above 100 K, is inextricably connected to the pseudogap phase, a range of energies that has very few electronic states associated with it. This phase appears well above the superconducting critical temperature Tc, and its origin is still under debate. It could be a consequence of a competing order or simply a precursor to superconductivity. Richter et al. studied the behavior of the electronic density of states (DOS) of a different superconducting system: the two-dimensional gas that appears at the interface between the insulators SrTiO3 and LaAlO3. Tunneling into the layer while modulating its carrier density by applying a gate voltage, the authors observed an energy gap in the DOS that behaved in a similar manner to the pseudogap in high-Tc copper oxide superconductors. Like the pseudogap, a gap in the DOS grows monotonically with carrier depletion and persists to temperatures far above the Tc. This similarity is surprising given the differences between the electronic structures of the two systems. What they do have in common, however, is dimensionality. Although copper oxides are three-dimensional compounds, they are layered, and most of the action happens in the two-dimensional planes. The authors thus suggest that the copper oxides' characteristic phase diagram might be related to the nature of two-dimensional superconductivity.

Nature 502, 528 (2013).

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