Atomic-resolution studies of epitaxial strain release mechanisms inLa1.85Sr0.15CuO4

Abstract

In this paper we present an atomic-resolution electron microscopy study of superlattices (SLs) where the colossal magnetoresistant manganite La 0.67 Ca 0.33 MnO 3 (LCMO) and the high critical temperature superconducting cuprate La 1.85 Sr 0.15 CuO 4 (LSCO) are combined. Although good quality epitaxial growth can be achieved, both the choice of substrate and the relatively large lattice mismatch between these materials (around 2%) have a significant impact on the system properties [Phys. C 468, 991 (2008); Nature (London) 394, 453 (1998)]. Our samples, grown by pulsed laser deposition, are epitaxial and exhibit high structural quality. By means of cutting-edge electron microscopy and spectroscopy techniques we still find that the epitaxial strain is accommodated by a combination of defects, such as interface steps and antiphase boundaries in the manganite. These defects result in inhomogeneous strain fields through the samples. Also, some chemical inhomogeneities are detected, up to the point that novel phases nucleate. For example, at the LCMO/LSCO interface the ABO 3 -type manganite adopts a tetragonal LSCO-like structure forming localized layers that locally resemble the composition of La 2/3 Ca 4/3 MnO 4 . Structural distortions are detected in the cuprate as well, which may extend over lateral distances of several unit cells. Finally, we also analyze the influence of the substrate-induced strain by examining superlattices grown on two different substrates: (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) and LaSrAlO 4 (LSAO). We observe that SLs grown on LSAT, which are nonsuperconducting, present reduced values of the c axis compared to superlattices grown on LSAO (which are fully superconducting). This finding points to the fact that the proper distance between copper planes in LSCO is essential in obtaining superconductivity in cuprates.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

“…4 and references therein). From the perspective of interfacial charge transfer and its impact on the overall materials properties of the YBCO/LCMO heterojunction, there has been a significant number of results including charge, spin and orbital reconstruction as revealed by electron microscopy1415161718, neutron reflectometry192021, resonant X-rays17222324252627, and cross-sectional STM1528, where the reported length scales of charge transfer effects range from few Å to several nanometers. The variability in scale of these charge transfer effects stems from the exploration of thick YBCO 7 and LCMO constituent layers of multiple unit cells (u.c.)…”

Superconductor to Mott insulator transition in YBa$_2$Cu$_3$O$_7$/LaCaMnO$_3$ heterostructures

“…4 and references therein). From the perspective of interfacial charge transfer and its impact on the overall materials properties of the YBCO/LCMO heterojunction, there has been a significant number of results including charge, spin and orbital reconstruction as revealed by electron microscopy [14][15][16][17][18], neutron reflectometry [19][20][21], resonant X-rays [17,[22][23][24][25][26][27], and cross-sectional STM [15,28], where the reported length scales of charge transfer effects range from a few Å to several nanometers. The variability in scale of these charge transfer effects stems from the exploration of thick YBCO 7 and LCMO constituent layers of multiple unit cells (u.c.)…”

Properties of LSMO/YBCO cross-strip type junctions

“…Therefore, such materials, and especially the CMR/HTS interface, are attractive for studying the interplay between two fundamental condensed-matter phenomena, superconductivity (S) and ferromagnetism (F). Recent developments in fabricating atomically smooth (flat) CMR/HTS interfaces in superlattices [1,2] provided an ideal system to investigate intriguing phenomena, such as a long-range proximity effect [3,4], spinpolarized quasiparticle injection into the HTS layer within a spin-diffusion length  FM [5], giant modulation of the CMR-layer magnetization induced by superconductivity [6], or charge transfer from CMR into HTS [7,8,9]. A variety of effects and phenomena at the SF interface offer possibilities of using these materials in different microelectronic and spintronic applications [10].…”