Unusual Suppression of the Superconducting Energy Gap and Critical Temperature in Atomically Thin NbSe2.
- Khestanova E School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Birkbeck J School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Zhu M School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Cao Y School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Yu GL School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Ghazaryan D School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Yin J School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Berger H Laboratory of Physics of Complex Matter (LPMC) , Ecole Polytechnique Fédérale de Lausanne , 1015 Lausanne , Switzerland.
- Forró L Laboratory of Physics of Complex Matter (LPMC) , Ecole Polytechnique Fédérale de Lausanne , 1015 Lausanne , Switzerland.
- Taniguchi T National Institute for Materials Science , 1-1 Namiki , Tsukuba , 305-0044 Japan.
- Watanabe K National Institute for Materials Science , 1-1 Namiki , Tsukuba , 305-0044 Japan.
- Gorbachev RV School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Mishchenko A School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Geim AK School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- Grigorieva IV School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , United Kingdom.
- 2018-03-13
Published in:
- Nano letters. - 2018
English
It is well-known that superconductivity in thin films is generally suppressed with decreasing thickness. This suppression is normally governed by either disorder-induced localization of Cooper pairs, weakening of Coulomb screening, or generation and unbinding of vortex-antivortex pairs as described by the Berezinskii-Kosterlitz-Thouless (BKT) theory. Defying general expectations, few-layer NbSe2, an archetypal example of ultrathin superconductors, has been found to remain superconducting down to monolayer thickness. Here, we report measurements of both the superconducting energy gap Δ and critical temperature TC in high-quality monocrystals of few-layer NbSe2, using planar-junction tunneling spectroscopy and lateral transport. We observe a fully developed gap that rapidly reduces for devices with the number of layers N ≤ 5, as does their TC. We show that the observed reduction cannot be explained by disorder, and the BKT mechanism is also excluded by measuring its transition temperature that for all N remains very close to TC. We attribute the observed behavior to changes in the electronic band structure predicted for mono- and bi- layer NbSe2 combined with inevitable suppression of the Cooper pair density at the superconductor-vacuum interface. Our experimental results for N > 2 are in good agreement with the dependences of Δ and TC expected in the latter case while the effect of band-structure reconstruction is evidenced by a stronger suppression of Δ and the disappearance of its anisotropy for N = 2. The spatial scale involved in the surface suppression of the density of states is only a few angstroms but cannot be ignored for atomically thin superconductors.
- Language
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- English
- Open access status
- green
- Identifiers
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- DOI 10.1021/acs.nanolett.8b00443
- PMID 29529377
- Persistent URL
- https://folia.unifr.ch/global/documents/120455
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