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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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Muon spin rotation signal.Time dependence of the muon decay asymmetry (proportional to the polarization) for muons implanted at 12.5 keV in the central underdoped layer (Tc′≲5 K) of the trilayer structure La1.84Sr0.16CuO4 (46 nm)/La1.94Sr0.06CuO4 (46 nm)/La1.84Sr0.16CuO4 (46 nm). An external magnetic field of 9.5 mT was applied parallel to the ab planes and to the interface (Meissner geometry). The signal at 40 K (black) represents the muon spin precession in the external field. At 9.5 K (red), well above Tc′, the lower precession frequency (proportional to the average local field) reflects the presence of diamagnetism in the barrier. Error bars indicate the statistical errors of the data, curves are fits to the data (see text for details).
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f5: Muon spin rotation signal.Time dependence of the muon decay asymmetry (proportional to the polarization) for muons implanted at 12.5 keV in the central underdoped layer (Tc′≲5 K) of the trilayer structure La1.84Sr0.16CuO4 (46 nm)/La1.94Sr0.06CuO4 (46 nm)/La1.84Sr0.16CuO4 (46 nm). An external magnetic field of 9.5 mT was applied parallel to the ab planes and to the interface (Meissner geometry). The signal at 40 K (black) represents the muon spin precession in the external field. At 9.5 K (red), well above Tc′, the lower precession frequency (proportional to the average local field) reflects the presence of diamagnetism in the barrier. Error bars indicate the statistical errors of the data, curves are fits to the data (see text for details).

Mentions: To map the diamagnetic response of the heterostructure as a function of position along the crystal c axis (z coordinate), we cooled the samples in ZF from above Tc to ~4.3 K, applied a magnetic field of 9.5 mT parallel to the ab planes (x direction) and collected μSR spectra as a function of the muon implantation energy at increasing temperatures. The weakly damped spin precession observed at an angular frequency ωL corresponding to a mean local field 〈Bx〉ωL/γμ (where γμ muon gyromagnetic ratio) exhibits the diamagnetic response of the heterostructure. This is clearly seen in Figure 5, which demonstrates the main result of this paper: at a temperature well above Tc′, the spins of the muons implanted in the barrier coherently precess in a field that is diamagnetically shifted with respect to the applied field. As the maximum diamagnetic shift is small (0.2–0.3 mT) for an applied field of 9.5 mT, and the experimentally measured field distribution resulting from weighting the profile Bx(z) with the implantation profile can be well approximated by a Gaussian distribution, the asymmetry term can be written as . 〈Bx〉 is obtained from a fit of the asymmetry spectra over a time interval (for t〉0.15–0.5 μs) where the fast relaxing parts give negligible contribution.


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)

Muon spin rotation signal.Time dependence of the muon decay asymmetry (proportional to the polarization) for muons implanted at 12.5 keV in the central underdoped layer (Tc′≲5 K) of the trilayer structure La1.84Sr0.16CuO4 (46 nm)/La1.94Sr0.06CuO4 (46 nm)/La1.84Sr0.16CuO4 (46 nm). An external magnetic field of 9.5 mT was applied parallel to the ab planes and to the interface (Meissner geometry). The signal at 40 K (black) represents the muon spin precession in the external field. At 9.5 K (red), well above Tc′, the lower precession frequency (proportional to the average local field) reflects the presence of diamagnetism in the barrier. Error bars indicate the statistical errors 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

f5: Muon spin rotation signal.Time dependence of the muon decay asymmetry (proportional to the polarization) for muons implanted at 12.5 keV in the central underdoped layer (Tc′≲5 K) of the trilayer structure La1.84Sr0.16CuO4 (46 nm)/La1.94Sr0.06CuO4 (46 nm)/La1.84Sr0.16CuO4 (46 nm). An external magnetic field of 9.5 mT was applied parallel to the ab planes and to the interface (Meissner geometry). The signal at 40 K (black) represents the muon spin precession in the external field. At 9.5 K (red), well above Tc′, the lower precession frequency (proportional to the average local field) reflects the presence of diamagnetism in the barrier. Error bars indicate the statistical errors of the data, curves are fits to the data (see text for details).
Mentions: To map the diamagnetic response of the heterostructure as a function of position along the crystal c axis (z coordinate), we cooled the samples in ZF from above Tc to ~4.3 K, applied a magnetic field of 9.5 mT parallel to the ab planes (x direction) and collected μSR spectra as a function of the muon implantation energy at increasing temperatures. The weakly damped spin precession observed at an angular frequency ωL corresponding to a mean local field 〈Bx〉ωL/γμ (where γμ muon gyromagnetic ratio) exhibits the diamagnetic response of the heterostructure. This is clearly seen in Figure 5, which demonstrates the main result of this paper: at a temperature well above Tc′, the spins of the muons implanted in the barrier coherently precess in a field that is diamagnetically shifted with respect to the applied field. As the maximum diamagnetic shift is small (0.2–0.3 mT) for an applied field of 9.5 mT, and the experimentally measured field distribution resulting from weighting the profile Bx(z) with the implantation profile can be well approximated by a Gaussian distribution, the asymmetry term can be written as . 〈Bx〉 is obtained from a fit of the asymmetry spectra over a time interval (for t〉0.15–0.5 μs) where the fast relaxing parts give negligible contribution.

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