Superconductivity and charge-carrier localization in ultrathin La_(1.85)Sr_(0.15)CuO₄/La₂CuO⁴ bilayers



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Sen, K. and Marsik, P. and Das, S. and Perret, E. and Andres Prada, R. de and Alberca, A. and Biškup, N. and Varela del Arco, María and Bernhard, C. (2017) Superconductivity and charge-carrier localization in ultrathin La_(1.85)Sr_(0.15)CuO₄/La₂CuO⁴ bilayers. Physical review B, 95 (21). ISSN 2469-9950

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La_(1.85)Sr_(0.15)CuO₄/La₂CuO₄ (LSCO15/LCO) bilayers with a precisely controlled thickness of N unit cells (UCs) of the former and M UCs of the latter ([LSCO15_N/LCO_M]) were grown on (001)- oriented SrLaAlO₄ (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2] bilayer is fully strained, whereas a [LSCO15_2/LCO_7] bilayer is already partially relaxed. The in situ monitoring of the growth with reflection high energy electron diffraction (RHEED) revealed that the gas environment during deposition has a surprisingly strong effect on the growth mode and thus on the amount of disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15 containing one CuO₂ plane each). For samples grown in pure N₂O gas (growth type B), the first LSCO15 UC next to the SLAO substrate is strongly disordered. This disorder is strongly reduced if the growth is performed in a mixture of N₂O and O₂ gas (growth type A). Electric transport measurements confirmed that the first UC of LSCO15 next to the SLAO substrate is highly resistive and shows no sign of superconductivity for growth type B, whereas it is superconducting for growth type A. Furthermore, we found, rather surprisingly, that the conductivity of the LSCO15 UC next to the LCO capping layer strongly depends on the thickness of the latter. A LCO capping layer with 7 UCs leads to a strong localization of the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity. The magnetotransport data suggest a similarity with the case of weakly hole doped LSCO single crystals that are in a so-called 'cluster-spin-glass state.' We discussed several mechanisms that could lead to such a localization of holes that are embedded in a short-range ordered antiferromagnetic background for the case of a thick LCO capping layer with M = 7 but not for a thin one with M = 2.

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©2017 American Physical Society.
The work at the University of Fribourg has been supported by the Schweizer Nationalfonds (SNF) through Grants No. 200020-153660, No. 200020-172611, and No. CRSII2-154410/1. Research at Universidad Complutense de Madrid has been sponsored by the Spanish MINECO Grant No. MAT2015-66888-C3-3-R and the European Research Council PoC MAGTOOLS #713251.

Uncontrolled Keywords:Thin-films; Interface superconductivity; Infrared ellipsometry; Superfluid density; La2-xsrxcuo4 films; Copper oxides; Phase-diagram; Temperature; Transition; Growth
Subjects:Sciences > Physics > Materials
Sciences > Physics > Solid state physics
ID Code:49681
Deposited On:25 Oct 2018 11:54
Last Modified:10 Jan 2019 18:47

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