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Quantum critical behaviour in the superfluid density of strongly underdoped ultrathin copper oxide films

Nature Physics volume 3, pages 700–702 (2007)Cite this article

Abstract

A central challenge in the physics of high-temperature superconductors is to understand superconductivity within a single copper oxide layer or bilayer, the fundamental structural unit, and how superconductivity is lost with underdoping of charge carriers. A seminal property of crystals and thick films1,2,3,4 is that when mobile holes are removed from optimally doped CuO2 planes, the transition temperature, Tc, and superfluid density, ns(0), decrease in a surprisingly correlated fashion. We elucidate the essential physics of strongly underdoped bilayers by studying two-dimensional (2D) samples near the critical doping level where superconductivity disappears. We report measurements of ns(T) in films of Y1−xCaxBa2Cu3O7−δ as thin as two copper oxide bilayers with Tc values as low as 3 K. In addition to seeing the 2D Kosterlitz–Thouless–Berezinski transition5,6 at Tc, we observe a remarkable scaling of Tc with ns(0), which indicates that the disappearance of superconductivity with underdoping is due to quantum fluctuations near a 2D quantum critical point.

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Figure 1: Superfluid density versus T for 2-unit-cell-thick Y1−xCaxBa2Cu3O7−δ films.
Figure 2: Scaling of Tc with superfluid density at T=0.

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Acknowledgements

We are grateful to Z. Tesanovic who greatly encouraged this investigation and provided many useful comments. We thank D. Stroud, C. Jayaprakash and Y. Zuev for many useful discussions. This work was supported in part by NSF-DMR grant 0203739. I.H. is grateful to The Ohio State University for an OSU Presidential Fellowship.

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  1. Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA

    Iulian Hetel, Thomas R. Lemberger & Mohit Randeria

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  1. Iulian Hetel
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  2. Thomas R. Lemberger
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Correspondence to Thomas R. Lemberger.

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Hetel, I., Lemberger, T. & Randeria, M. Quantum critical behaviour in the superfluid density of strongly underdoped ultrathin copper oxide films. Nature Phys 3, 700–702 (2007). https://doi.org/10.1038/nphys707

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