Lean Supercurrents



Figure 1: In two-dimensional materials like thin films, the formation of Cooper pairs and long-range coherence between the pairs may not occur at the same temperature. This may explain why the T_c of a film determined from transport and scanning tunneling spectroscopy (STS) measurements is different.

 Viewpoint: Supercurrents Get Lean


Electron transport measurements on thin films reveal whether two-dimensional metals support macroscopic supercurrents.
Chih-Kang Shih, and Gregory A. Fiete, Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA

Published November 7, 2011
Physics 4, 92 (2011)
DOI: 10.1103/Physics.4.92

For a material to transition into a superconducting state, two things have to happen: the electrons must form Cooper pairs (the carriers of superconducting current) and the pairs have to condense into a single phase. In low-dimensional materials, quantum fluctuations may disrupt the superconducting phase even when the Cooper pairs are able to form, leading to the question: How thin can a material be and still superconduct? Advances in synthesizing high-quality, ultrathin metal films have provided unprecedented opportunities to address this question. Experimental evidence suggests that superconductivity persists with a similar transition temperature, T_c , even in films that are only 1 –2 atomic layers thick [1, 2]; however, these experiments have been based primarily on scanning tunneling spectroscopy, which detects the Cooper pairs, but not the existence of a macroscopic supercurrent. Whether an atomically thin film would also support supercurrents has therefore remained an open question. Now, in a paper appearing in Physical Review Letters, Takashi Uchihashi and co-workers at the National Institute for Materials Science in Tsukuba, Japan, provide a definite answer to this question by showing that robust supercurrents flow over macroscopic distances in an atomically thin metal film of indium [3]. Their work is likely to push theorists and experimentalists to revisit the current understanding of low-dimensional superconductivity.

American Physical Society: Viewpoint: Supercurrents Get Lean