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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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μSR spectra in ZF.(a) ZF asymmetry spectra from the single UD layer (black squares T=40 K , red circles 8.3 K, blue triangles 6.3 K, magenta diamonds 4.6 K). (b) Spectra from the trilayer OP/UD/OP structure (black squares 40 K, red circles 8.0 K, blue triangles 6.0 K, magenta diamonds 4.4 K). The energy is chosen in both cases to stop the muons at the centre of the UD layer. The pronounced depolarization at low temperatures and its evolution is similar in both cases. The higher baseline in the trilayer case reflects essentially the ~17% weakly relaxing contribution of the top layer. Error bars indicate the statistical uncertainty of the data, curves are fits to the data (see text for details).
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f3: μSR spectra in ZF.(a) ZF asymmetry spectra from the single UD layer (black squares T=40 K , red circles 8.3 K, blue triangles 6.3 K, magenta diamonds 4.6 K). (b) Spectra from the trilayer OP/UD/OP structure (black squares 40 K, red circles 8.0 K, blue triangles 6.0 K, magenta diamonds 4.4 K). The energy is chosen in both cases to stop the muons at the centre of the UD layer. The pronounced depolarization at low temperatures and its evolution is similar in both cases. The higher baseline in the trilayer case reflects essentially the ~17% weakly relaxing contribution of the top layer. Error bars indicate the statistical uncertainty of the data, curves are fits to the data (see text for details).

Mentions: We first discuss the magnetic properties of the UD layer grown as a SL or as a barrier in the trilayer structure (TL). The comparison of the magnetic behaviour in the two cases, which strongly depends on the doping level, allows us to assess the equivalence and integrity of the layers. For this we implant in the centre of the layer muons with 5.3 and 12.5 keV, respectively, and record muon spin precession/relaxation spectra at zero field (ZF) and in a field Bext=9.5 mT applied parallel to the ab planes and transverse to the initial muon spin polarization (TF). Typical ZF μSR asymmetry spectra, which are proportional to the muon polarization, A(t)=A0P(t), are shown in Figure 3. The time evolution of the polarization of the muons implanted in the layer can be consistently fitted in both cases by a combination of a fast relaxing and a slowly relaxing component. (In the top and bottom OP layers only the component weakly relaxing due to the small nuclear moments is present, reflecting the absence of magnetism in these layers).


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)

μSR spectra in ZF.(a) ZF asymmetry spectra from the single UD layer (black squares T=40 K , red circles 8.3 K, blue triangles 6.3 K, magenta diamonds 4.6 K). (b) Spectra from the trilayer OP/UD/OP structure (black squares 40 K, red circles 8.0 K, blue triangles 6.0 K, magenta diamonds 4.4 K). The energy is chosen in both cases to stop the muons at the centre of the UD layer. The pronounced depolarization at low temperatures and its evolution is similar in both cases. The higher baseline in the trilayer case reflects essentially the ~17% weakly relaxing contribution of the top layer. Error bars indicate the statistical uncertainty of the data, curves are fits to the data (see text for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: μSR spectra in ZF.(a) ZF asymmetry spectra from the single UD layer (black squares T=40 K , red circles 8.3 K, blue triangles 6.3 K, magenta diamonds 4.6 K). (b) Spectra from the trilayer OP/UD/OP structure (black squares 40 K, red circles 8.0 K, blue triangles 6.0 K, magenta diamonds 4.4 K). The energy is chosen in both cases to stop the muons at the centre of the UD layer. The pronounced depolarization at low temperatures and its evolution is similar in both cases. The higher baseline in the trilayer case reflects essentially the ~17% weakly relaxing contribution of the top layer. Error bars indicate the statistical uncertainty of the data, curves are fits to the data (see text for details).
Mentions: We first discuss the magnetic properties of the UD layer grown as a SL or as a barrier in the trilayer structure (TL). The comparison of the magnetic behaviour in the two cases, which strongly depends on the doping level, allows us to assess the equivalence and integrity of the layers. For this we implant in the centre of the layer muons with 5.3 and 12.5 keV, respectively, and record muon spin precession/relaxation spectra at zero field (ZF) and in a field Bext=9.5 mT applied parallel to the ab planes and transverse to the initial muon spin polarization (TF). Typical ZF μSR asymmetry spectra, which are proportional to the muon polarization, A(t)=A0P(t), are shown in Figure 3. The time evolution of the polarization of the muons implanted in the layer can be consistently fitted in both cases by a combination of a fast relaxing and a slowly relaxing component. (In the top and bottom OP layers only the component weakly relaxing due to the small nuclear moments is present, reflecting the absence of magnetism in these layers).

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