Metallic ground state in an ion-gated two-dimensional superconductor

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Science  23 Oct 2015:
Vol. 350, Issue 6259, pp. 409-413
DOI: 10.1126/science.1259440

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A 3D approach to make 2D superconductors

When the thickness of a superconducting film becomes comparable to the typical size of its electron pairs, its superconductivity enters a two-dimensional (2D) regime. Thinner films usually have higher amounts of disorder, making it difficult to isolate the 2D effects. To circumvent this limitation, Saito et al. induced charge carriers on the surface of the 3D insulator ZrNCl. This approach produced a clean superconducting layer thinner than the unit cell of the crystal. The superconducting state was extremely sensitive to the application of a perpendicular magnetic field, as expected for clean systems.

Science, this issue p. 409


Recently emerging two-dimensional (2D) superconductors in atomically thin layers and at heterogeneous interfaces are attracting growing interest in condensed matter physics. Here, we report that an ion-gated zirconium nitride chloride surface, exhibiting a dome-shaped phase diagram with a maximum critical temperature of 14.8 kelvin, behaves as a superconductor persisting to the 2D limit. The superconducting thickness estimated from the upper critical fields is ≅ 1.8 nanometers, which is thinner than one unit-cell. The majority of the vortex phase diagram down to 2 kelvin is occupied by a metallic state with a finite resistance, owing to the quantum creep of vortices caused by extremely weak pinning and disorder. Our findings highlight the potential of electric-field–induced superconductivity, establishing a new platform for accessing quantum phases in clean 2D superconductors.

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