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Terashima, Takahito; Shimura, Kei; Bandō, Yoshichika; Matsuda, Yuji; Fujiyama, A.; Komiyama, S.

doi:10.1103/physrevlett.67.1362

Cited by 229 publications

(79 citation statements)

References 17 publications

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“…T c values agree with previously reported data on similar superlattices [8,12]. The T c dependence on YBCO thickness has been reported previously in trilayer samples and single films [10,13,14]. We found a systematic and monotonous increase of the c parameter when YBCO layer thickness increases from 1 to 12 unit cells approaching the value reported for single 1000 Å thick films (see Fig.…”

supporting

confidence: 92%

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
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The structure of high quality ͓YBCO N ͞PBCO M ͔ 1000 ± A superlattices, with N ranging between 1 and 12 unit cells and M 5 unit cells, grown by high oxygen pressure sputtering, is analyzed. Intracell atomic structure of the layers along the c axis and disorder at interfaces is investigated using an x-ray refinement technique. Negligible roughness, step disorder, and interdiffusion are found at the interfaces. Epitaxial mismatch strain results in a surprising reorganization of interatomic distances for the thinnest YBCO layers, which seems to correlated with the decrease in the critical temperature. Intracell structure is invoked as an additional source of T c changes in very thin YBCO layers. PACS numbers: 74.76.Bz, 61.10.Nz, 68.65. + g Since the discovery of the high T c superconductivity, structure has been recognized to play a crucial role towards the understanding of its nature and mechanisms. It has been known for years that distortions arising from cation substitution can produce significant changes in T c [1], and recent experiments on doped La 2 CuO 4 superconductors at constant carrier concentration show a clear dependence of T c on lattice strains [2]. A great effort has been put in structure determination under hydrostatic pressure [3]. Epitaxial stress in thin films offers a simple way to arrive at a strain pattern not attainable under hydrostatic pressure [4]: According to the Poisson effect, film growth on a substrate with slightly smaller (larger) in-plane lattice parameters may lead to a compression (expansion) in the ab plane that can result in an expansion (contraction) in the out-ofplane direction. Uniaxial epitaxial strain, together with Poisson's ratios, has been addressed before [5]. However, the general applicability of the Poisson effect to thin films is still doubtful [6], especially in these highly anisotropic materials. Anyway, Locquet et al. [7] have been able to double the critical temperature in the La 1.9 Sr 0.1 CuO 4 high T c superconductor using mismatch strain. They show that compressive epitaxial strain in-plane can generate much larger increases in T c than those obtained by comparable hydrostatic pressures, and their claim is that the distance relevant to the mechanism of the superconductivity being modified is the separation between consecutive CuO 2 planes. Mismatch strain constitutes an alternative way to change the intracell distances which may be "relevant" to the mechanism of superconductivity, but a quantitative structure analysis of strained films is necessary. X-ray diffraction is a widely used technique to analyze structure, which supplies structural information averaged over a length scale (structural coherence length) which may be around a hundred angstroms. The extraction of quantitative information requires the fit of the diffraction pattern to a structure model containing a large number of parameters in these complex materials, and, therefore, results may not be very reliable for single epitaxial films, which usually show a reduced number of diffraction peak...

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supporting

confidence: 92%

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
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“…Another source of Tc depression in ultrathin layers is the reduced dimensionality [9]. In this context, we compare the depression of the critical temperature when the YBCO thickness is reduced in presence of magnetic (LCMO) and non magnetic (PrBa 2 Cu 3 O 7 ) layers with similar (fixed) thickness.…”

Section: Ferromagnetic (F) / Superconductor (S) Heterostructures Havementioning

confidence: 99%

Superconductivity depression in ultrathin YBa2Cu3O7−δ layers in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices

Sefrioui¹,

Varela²,

Peña³

et al. 2002

Applied Physics Letters

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We report on the depression of the superconducting critical temperature of ultra superlattices. The thickness of the manganite layer is kept at 15 unit cells and the YBCO thickness is varied between N=12 and N=1 unit cells. The structural analysis using x-ray diffraction and electron microscopy shows sharp interfaces with little structural disorder. While a critical temperature, Tc=85 K is found for 12 YBCO unit cells, superconductivity is completely suppressed for YBCO layer thickness below 3 unit cells. The possible interaction between superconductivity and magnetism is investigated.2 Ferromagnetic (F) / superconductor (S) heterostructures have recently attracted much interest for applications in spin injection (three terminal) devices [1]. High Tc superconductors (HTS) and colossal magnetoresistance (CMR) oxides are interesting candidate materials because the low carrier density of the HTS and the almost full spin polarization of the CMR oxides can be combined to yield high sensitivity (gain) fast devices. A reduction of the critical current consistent with suppression of superconductivity by spin polarized quasiparticle injection has been reported by several groups in recent years [2,3], opening the door to practical devices based on complex oxides. The samples reported so far involve quite thick (50-100 nm ) YBCO layers, thus shadowing interface effects. However, interface properties are expected to play a dominant role in the physics of CMR/HTS F/S heterostructures, and extrinsic (interface alloying or roughness) or intrinsic factors (proximity effect) may deeply influence the performance of the devices. The use of superlattices (instead of bilayers) allows an in depth characterization of the interfaces with conventional structure probes like x-ray diffraction (XRD) or transmission electron microscopy (TEM). The presence of magnetism and superconductivity in this kind of samples has been reported before [4,5].In this letter we report on the growth of LCMO/YBCO superlattices with ultrathin (1 to 12 unit cells) YBCO layers and fixed LCMO thickness (15 unit cells), to investigate how robust is the superconductivity of the YBCO when its thickness is reduced in presence of magnetic layers. We have found that superconductivity is depressed in presence of the adjacent LCMO layers. A structural analysis with XRD and TEM is used to explore the influence of interface disorder on the depression of the superconductivity.Samples were grown in a high pressure (3.4 mbar) pure oxygen sputtering system at high temperatures (900 ºC). Individual YBCO films on STO (100) given the small thickness of the layer is consistent with the absence of interdiffusion.At this point it seems very unlikely that the systematic depression of the critical temperature when the YBCO thickness is reduced might result of extrinsic factors like deoxygenation or roughness. Another source of Tc depression in ultrathin layers is the reduced dimensionality [9]. In this context, we compare the depression of the critical temperature when the Y...

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“…For example, many fundamental studies of high-T c superconductors are based on measurements of ultrathin layers, where a one unit cell thick layer constitutes an attractive system to investigate dimensionality effects in vortex matter or the nature of high-T c superconductivity itself [1,2]. However, even though the possibility of growing a single unit cell coherently over large lateral distances has been debated in recent years, it still remains an open question [3,4].…”

mentioning

confidence: 99%

Direct Evidence for Block-by-Block Growth in High-Temperature Superconductor Ultrathin Films

et al. 2001

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Charge neutrality and stoichiometry impose severe restrictions on the mechanisms of epitaxial growth of complex oxides. The fundamental question arises of what is the minimum growth unit when sample thickness is reduced beyond the size of the unit cell. We have investigated the growth mechanism of YBa 2 Cu 3 O 7 cuprate superconductor, using a consistent approach based on the growth of noninteger numbers of YBa 2 Cu 3 O 7 layers in YBa 2 Cu 3 O 7 ͞PrBa 2 Cu 3 O 7 superlattices. Ex situ chemical and structural analysis evidence a 2D block-by-block mechanism in which the minimum growth units are complete unit cell blocks, growing coherently over large lateral distances.

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Superconductivity of one-unit-cell thickYBa2Cu3

Cited by 229 publications

References 17 publications

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
View full text Add to dashboard Cite

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
View full text Add to dashboard Cite

Superconductivity depression in ultrathin YBa2Cu3O7−δ layers in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices

Direct Evidence for Block-by-Block Growth in High-Temperature Superconductor Ultrathin Films

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Superconductivity of one-unit-cell thickYBa2Cu3

Cited by 229 publications

References 17 publications

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−xVarela1, Sefrioui2, Arias3 et al. 1999Phys. Rev. Lett.729572View full textAdd to dashboardCite

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−xVarela1, Sefrioui2, Arias3 et al. 1999Phys. Rev. Lett.729572View full textAdd to dashboardCite

Superconductivity depression in ultrathin YBa2Cu3O7−δ layers in La0.7Ca0.3MnO3/YBa2Cu3O7−δ superlattices

Direct Evidence for Block-by-Block Growth in High-Temperature Superconductor Ultrathin Films

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Product

Resources

About

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
View full text Add to dashboard Cite

Intracell Changes in Epitaxially StrainedYBa2Cu3O7−x
Varela
¹
,
Sefrioui
²
,
Arias
³

et al. 1999
Phys. Rev. Lett.
72
9
57
2
View full text Add to dashboard Cite