Thickness dependence of the superconducting transition temperature of YBCO

Chan, I. N.; Vier, D. C.; Nakamura, Osamu; Hasen, J.; Guimpel, J.; Schultz, S.; Schuller, Iván K.

doi:10.1016/0375-9601(93)90834-m

Cited by 23 publications

(20 citation statements)

References 18 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.…”

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confidence: 82%

mentioning

confidence: 99%

“…We show that intralayer epitaxial strain is responsible for pronounced nonuniform changes in intracell distances of the YBCO. We propose that, besides dimensionality or proximity effects, these structural changes may be responsible for the changes in the critical temperature resulting from modifications of the electronic structure, and may add information to the long debated question of the superconductivity of ultrathin layers [9,10].The samples for this study were epitaxial YBCO͞PBCO superlattices grown on (100) SrTiO 3 using a high pressure (3.6 mbar pure oxygen) multitarget sputtering system. High pressure oxygen atmosphere yields a very thermalized growth at a very slow rate, 8 Å͞min for YBCO, which allows an accurate control of film 3936 0031-9007͞99͞83(19)͞3936(4)$15.00…”

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confidence: 99%

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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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confidence: 82%

mentioning

confidence: 99%

mentioning

confidence: 99%

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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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“…We analyze the structure of ultrathin layers with thickness decreasing from a hundred angstroms to one unit cell. Although the thickness dependence of T c for very thin layers has been widely discussed in recent past, 8 the issue of the superconductivity of a single unit cell has been long debated and remains an open question. 9,10 Our study indicates that epitaxial strain for YBCO thickness below 4 unit cells, causes important changes in interatomic distances.…”

Section: Introductionmentioning

confidence: 99%

Epitaxial mismatch strain inYBa2Cu3O7−
Varela
¹
,
Arias
²
,
Sefrioui
³

et al. 2000
Phys. Rev. B
17
1
20
1
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The effects of epitaxial strain in ultrathin YBa 2 Cu 3 O 7Ϫ␦ layers have been investigated by x-ray diffraction and transmission electron microscopy. The samples used were high quality ͓YBa 2 Cu 3 O 7Ϫ␦ (YBCO) N / PrBa 2 Cu 3 O 7 (PBCO) M ͔ 1000 Å superlattices, grown by high oxygen pressure sputtering, with N ranging between 1 and 12 unit cells and M ϭ5 unit cells. Superlattice structure is refined by fitting x-ray spectra to a structural model containing disorder related parameters. Epitaxial mismatch strain and the absence of step disorder are found for YBCO layer thickness below 4 unit cells. A surprising reorganization of interatomic distances results, which seems to correlate with the decrease in the critical temperature. For larger YBCO layer thickness, stress relaxes and step disorder builds up. Transmission electron microscopy observations show the presence of a-axis orientated microdomains, which seem to be correlated to the release of epitaxial strain, provided in plane mismatch is smaller in this orientation.

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“…[5][6][7][8][9] Examples where the interaction strength is modified can be constructed following similar principles. The ''123'' UC contains two ''interaction'' layers and one charge reservoir.…”

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confidence: 99%

Local determination of the stacking sequence of layered materials

Fompeyrine

Berger

Lang

et al. 1998

Applied Physics Letters

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The ability to modify the stacking sequence of ultrathin films offers a unique way to change either the interaction strength or the doping, but demands a careful control of each atomic monolayer. Progress is hampered by the lack of a direct method that allows differentiation on a local scale between the various terminating layers of a crystal. Here, the combination of a vacuum annealing process and friction force microscopy reveals this local distinction on a SrTiO3 surface. Using the friction contrast, we find how the terminating layer of a single crystal profoundly influences the terrace edge structure.

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Thickness dependence of the superconducting transition temperature of YBCO

Cited by 23 publications

References 18 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

Epitaxial mismatch strain inYBa2Cu3O7−
Varela
¹
,
Arias
²
,
Sefrioui
³

et al. 2000
Phys. Rev. B
17
1
20
1
View full text Add to dashboard Cite

Local determination of the stacking sequence of layered materials

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Thickness dependence of the superconducting transition temperature of YBCO

Cited by 23 publications

References 18 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

Epitaxial mismatch strain inYBa2Cu3O7−Varela1, Arias2, Sefrioui3 et al. 2000Phys. Rev. B171201View full textAdd to dashboardCite

Local determination of the stacking sequence of layered materials

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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

Epitaxial mismatch strain inYBa2Cu3O7−
Varela
¹
,
Arias
²
,
Sefrioui
³

et al. 2000
Phys. Rev. B
17
1
20
1
View full text Add to dashboard Cite