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The Meissner effect in a strongly underdoped cuprate above its critical temperature.

Morenzoni E, Wojek BM, Suter A, Prokscha T, Logvenov G, Božović I - Nat Commun (2011)

Bottom Line: The Meissner effect and associated perfect 'bulk' diamagnetism together with zero resistance and gap opening are characteristic features of the superconducting state.In the pseudogap state of cuprates, unusual diamagnetic signals and anomalous proximity effects have been detected, but a Meissner effect has never been observed.The temperature dependence of the effective penetration depth and superfluid density in different layers indicates that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity to optimally doped layers, but this induced order is sensitive to thermal excitation.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. elvezio.morenzoni@psi.ch

ABSTRACT
The Meissner effect and associated perfect 'bulk' diamagnetism together with zero resistance and gap opening are characteristic features of the superconducting state. In the pseudogap state of cuprates, unusual diamagnetic signals and anomalous proximity effects have been detected, but a Meissner effect has never been observed. Here we probe the local diamagnetic response in the normal state of an underdoped La(1.94)Sr(0.06)CuO(4) layer (T(c)'≤5 K), which is brought into close contact with two nearly optimally doped La(1.84)Sr(0.16)CuO(4) layers (T(c)≈32 K). We show that the entire 'barrier' layer of thickness, much larger than the typical c axis coherence lengths of cuprates, exhibits a Meissner effect at temperatures above T(c)' but below T(c). The temperature dependence of the effective penetration depth and superfluid density in different layers indicates that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity to optimally doped layers, but this induced order is sensitive to thermal excitation.

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Sample characterization.(a) The inductive response of three La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayers (filled symbols) and four single-phase La1.94Sr0.06CuO4 films (open symbols). Each set was deposited simultaneously and under nominally identical conditions. (b) X-ray reflectivity of a trilayer film. The Kiessig fringes reflecting the finite film thickness indicate atomically smooth surface and interfaces. The continuous curve is a fit to the data obtained with the GenX routine33. (c) XRD data of a trilayer film showing the finite-thickness oscillations in the vicinity of the (002) Bragg reflection. (d) Typical Rutherford backscattering spectrum of a trilayer film. The curve is a simulation obtained by the RUMP program34 including multiple scattering effects and gives a total thickness of 140 nm (±4 nm). The rms surface roughness as measured by atomic force microscopy is smaller than 0.5 nm over an area of 2,500 μm2.
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f2: Sample characterization.(a) The inductive response of three La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayers (filled symbols) and four single-phase La1.94Sr0.06CuO4 films (open symbols). Each set was deposited simultaneously and under nominally identical conditions. (b) X-ray reflectivity of a trilayer film. The Kiessig fringes reflecting the finite film thickness indicate atomically smooth surface and interfaces. The continuous curve is a fit to the data obtained with the GenX routine33. (c) XRD data of a trilayer film showing the finite-thickness oscillations in the vicinity of the (002) Bragg reflection. (d) Typical Rutherford backscattering spectrum of a trilayer film. The curve is a simulation obtained by the RUMP program34 including multiple scattering effects and gives a total thickness of 140 nm (±4 nm). The rms surface roughness as measured by atomic force microscopy is smaller than 0.5 nm over an area of 2,500 μm2.

Mentions: To enhance the signal-to-noise ratio, the μSR measurements of the trilayers were done simultaneously on a set of three nominally identical films (3 cm2 total area). For the single layers (SLs), the set consisted of four films (4 cm2 total area). Figure 2a shows that all the trilayers have sharp superconducting transitions with Tc≈32 K with very small variations in Tc within the set of three trilayer films. In contrast, all single-phase La1.94Sr0.06CuO4 films show Tc′≲5 K. Here, the variations in Tc within the set are somewhat larger; they are probably due to small variations in the Sr doping level or in the density of oxygen vacancies, and the greater sensitivity of Tc to such variations for doping in the vicinity of the superconductor–insulator transition. Note, however, that this does not affect our conclusion in the paper. Figure 2b and c shows reflectivity and XRD, respectively, from a La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayer measured at room temperature on a Seifert XRD 3003 PTS with a 4 Ge 220 crystal monochromator, providing Cu Kα1 radiation with wavelength 0.15406 nm. The XRD patterns show very high crystallinity and absence of secondary phases. Rocking curves with full-width at half-maximum smaller than 0.015° and finite-thickness oscillations visible in low angle reflectivity curves and around the (002n) Bragg peaks (n=1,2,3) indicate the high quality of the films and interfaces. From the finite thickness oscillations the overall film thickness has been determined to be 136±1 nm, consistent with the values determined by Rutherford backscattering (Fig. 2d). The root mean square (r.m.s.) roughness of the interfaces as obtained from the fit of the X-ray reflectivity curve is about 1 nm. The typical surface roughness determined by AFM was 0.5 nm, much less than one-unit-cell height (1.3 nm).


The Meissner effect in a strongly underdoped cuprate above its critical temperature.

Morenzoni E, Wojek BM, Suter A, Prokscha T, Logvenov G, Božović I - Nat Commun (2011)

Sample characterization.(a) The inductive response of three La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayers (filled symbols) and four single-phase La1.94Sr0.06CuO4 films (open symbols). Each set was deposited simultaneously and under nominally identical conditions. (b) X-ray reflectivity of a trilayer film. The Kiessig fringes reflecting the finite film thickness indicate atomically smooth surface and interfaces. The continuous curve is a fit to the data obtained with the GenX routine33. (c) XRD data of a trilayer film showing the finite-thickness oscillations in the vicinity of the (002) Bragg reflection. (d) Typical Rutherford backscattering spectrum of a trilayer film. The curve is a simulation obtained by the RUMP program34 including multiple scattering effects and gives a total thickness of 140 nm (±4 nm). The rms surface roughness as measured by atomic force microscopy is smaller than 0.5 nm over an area of 2,500 μm2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3104550&req=5

f2: Sample characterization.(a) The inductive response of three La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayers (filled symbols) and four single-phase La1.94Sr0.06CuO4 films (open symbols). Each set was deposited simultaneously and under nominally identical conditions. (b) X-ray reflectivity of a trilayer film. The Kiessig fringes reflecting the finite film thickness indicate atomically smooth surface and interfaces. The continuous curve is a fit to the data obtained with the GenX routine33. (c) XRD data of a trilayer film showing the finite-thickness oscillations in the vicinity of the (002) Bragg reflection. (d) Typical Rutherford backscattering spectrum of a trilayer film. The curve is a simulation obtained by the RUMP program34 including multiple scattering effects and gives a total thickness of 140 nm (±4 nm). The rms surface roughness as measured by atomic force microscopy is smaller than 0.5 nm over an area of 2,500 μm2.
Mentions: To enhance the signal-to-noise ratio, the μSR measurements of the trilayers were done simultaneously on a set of three nominally identical films (3 cm2 total area). For the single layers (SLs), the set consisted of four films (4 cm2 total area). Figure 2a shows that all the trilayers have sharp superconducting transitions with Tc≈32 K with very small variations in Tc within the set of three trilayer films. In contrast, all single-phase La1.94Sr0.06CuO4 films show Tc′≲5 K. Here, the variations in Tc within the set are somewhat larger; they are probably due to small variations in the Sr doping level or in the density of oxygen vacancies, and the greater sensitivity of Tc to such variations for doping in the vicinity of the superconductor–insulator transition. Note, however, that this does not affect our conclusion in the paper. Figure 2b and c shows reflectivity and XRD, respectively, from a La1.84Sr0.16CuO4/La1.94Sr0.06CuO4/La1.84Sr0.16CuO4 trilayer measured at room temperature on a Seifert XRD 3003 PTS with a 4 Ge 220 crystal monochromator, providing Cu Kα1 radiation with wavelength 0.15406 nm. The XRD patterns show very high crystallinity and absence of secondary phases. Rocking curves with full-width at half-maximum smaller than 0.015° and finite-thickness oscillations visible in low angle reflectivity curves and around the (002n) Bragg peaks (n=1,2,3) indicate the high quality of the films and interfaces. From the finite thickness oscillations the overall film thickness has been determined to be 136±1 nm, consistent with the values determined by Rutherford backscattering (Fig. 2d). The root mean square (r.m.s.) roughness of the interfaces as obtained from the fit of the X-ray reflectivity curve is about 1 nm. The typical surface roughness determined by AFM was 0.5 nm, much less than one-unit-cell height (1.3 nm).

Bottom Line: The Meissner effect and associated perfect 'bulk' diamagnetism together with zero resistance and gap opening are characteristic features of the superconducting state.In the pseudogap state of cuprates, unusual diamagnetic signals and anomalous proximity effects have been detected, but a Meissner effect has never been observed.The temperature dependence of the effective penetration depth and superfluid density in different layers indicates that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity to optimally doped layers, but this induced order is sensitive to thermal excitation.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. elvezio.morenzoni@psi.ch

ABSTRACT
The Meissner effect and associated perfect 'bulk' diamagnetism together with zero resistance and gap opening are characteristic features of the superconducting state. In the pseudogap state of cuprates, unusual diamagnetic signals and anomalous proximity effects have been detected, but a Meissner effect has never been observed. Here we probe the local diamagnetic response in the normal state of an underdoped La(1.94)Sr(0.06)CuO(4) layer (T(c)'≤5 K), which is brought into close contact with two nearly optimally doped La(1.84)Sr(0.16)CuO(4) layers (T(c)≈32 K). We show that the entire 'barrier' layer of thickness, much larger than the typical c axis coherence lengths of cuprates, exhibits a Meissner effect at temperatures above T(c)' but below T(c). The temperature dependence of the effective penetration depth and superfluid density in different layers indicates that superfluidity with long-range phase coherence is induced in the underdoped layer by the proximity to optimally doped layers, but this induced order is sensitive to thermal excitation.

Show MeSH
Related in: MedlinePlus