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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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Signal amplitudes and relaxation rates.(a) Temperature dependence of the relative fractions of fast (f, circles) and slowly (s, squares) relaxing components for a 46-nm thick underdoped La1.94Sr0.06CuO4 layer as a single-phase film (E=5.3 keV, open symbols) or as barrier in a trilayer heterostructure (E=12.5 keV, closed symbols). (b) Corresponding relaxation rates (proportional to the width of the field distribution) for both configurations. Note the increase in amplitude of the fast relaxing component below ~15 K indicating the development of disordered magnetism. Error bars give the fit errors.
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f4: Signal amplitudes and relaxation rates.(a) Temperature dependence of the relative fractions of fast (f, circles) and slowly (s, squares) relaxing components for a 46-nm thick underdoped La1.94Sr0.06CuO4 layer as a single-phase film (E=5.3 keV, open symbols) or as barrier in a trilayer heterostructure (E=12.5 keV, closed symbols). (b) Corresponding relaxation rates (proportional to the width of the field distribution) for both configurations. Note the increase in amplitude of the fast relaxing component below ~15 K indicating the development of disordered magnetism. Error bars give the fit errors.

Mentions: To analyse the temperature scans in the transverse field case, the As and Atb terms in equation (1) are multiplied by an oscillating term. Figure 4 shows the temperature dependence of the amplitude of Af and As and their relaxation rates (λf and λs) in this case. The relaxation rate is a measure of the width of the distribution of local magnetic fields (λ≃γμΔB), which is proportional to the size of the magnetic moments, but also may include contributions from fluctuating fields. The emergence of λf below ~15 K is due to the build up of random static fields from Cu electronic moments. The fact that we observe two distinct μSR signals in TF and ZF means that we have two spatially separated phases. A fraction Af/(Af+As) of the muons probes a magnetic phase, whereas the others experience only very weak magnetic fields. The non-observation of a spontaneous spin precession shows that the magnetic phase originates from the moments that slow down and freeze with random orientation producing a distribution of random static fields. In La2−xSrxCuO4 this short-range antiferromagnetic correlated spin-glass-like state (sometimes termed cluster spin-glass) is known to persist at x〉0.02 coexisting with superconductivity in the strongly UD regime 0.05〈x〈0.1 (ref. 16). The magnetic structure is heterogeneous on a length scale larger than a few nm, as the fields produced by the copper magnetic moments decay away over this length scale. The evolution with temperature of the signals shows that, while the total amplitude remains constant, the magnetic phase begins to appear below about 15 K and gradually grows at the expense of the other as the temperature decreases (see Fig. 4). Unlike Af(T), λf is almost temperature independent. This indicates that the disorder and size of the moments immediately saturate on freezing, whereas an increasing volume fraction of the UD layer becomes magnetic as the temperature is lowered further.


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)

Signal amplitudes and relaxation rates.(a) Temperature dependence of the relative fractions of fast (f, circles) and slowly (s, squares) relaxing components for a 46-nm thick underdoped La1.94Sr0.06CuO4 layer as a single-phase film (E=5.3 keV, open symbols) or as barrier in a trilayer heterostructure (E=12.5 keV, closed symbols). (b) Corresponding relaxation rates (proportional to the width of the field distribution) for both configurations. Note the increase in amplitude of the fast relaxing component below ~15 K indicating the development of disordered magnetism. Error bars give the fit errors.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Signal amplitudes and relaxation rates.(a) Temperature dependence of the relative fractions of fast (f, circles) and slowly (s, squares) relaxing components for a 46-nm thick underdoped La1.94Sr0.06CuO4 layer as a single-phase film (E=5.3 keV, open symbols) or as barrier in a trilayer heterostructure (E=12.5 keV, closed symbols). (b) Corresponding relaxation rates (proportional to the width of the field distribution) for both configurations. Note the increase in amplitude of the fast relaxing component below ~15 K indicating the development of disordered magnetism. Error bars give the fit errors.
Mentions: To analyse the temperature scans in the transverse field case, the As and Atb terms in equation (1) are multiplied by an oscillating term. Figure 4 shows the temperature dependence of the amplitude of Af and As and their relaxation rates (λf and λs) in this case. The relaxation rate is a measure of the width of the distribution of local magnetic fields (λ≃γμΔB), which is proportional to the size of the magnetic moments, but also may include contributions from fluctuating fields. The emergence of λf below ~15 K is due to the build up of random static fields from Cu electronic moments. The fact that we observe two distinct μSR signals in TF and ZF means that we have two spatially separated phases. A fraction Af/(Af+As) of the muons probes a magnetic phase, whereas the others experience only very weak magnetic fields. The non-observation of a spontaneous spin precession shows that the magnetic phase originates from the moments that slow down and freeze with random orientation producing a distribution of random static fields. In La2−xSrxCuO4 this short-range antiferromagnetic correlated spin-glass-like state (sometimes termed cluster spin-glass) is known to persist at x〉0.02 coexisting with superconductivity in the strongly UD regime 0.05〈x〈0.1 (ref. 16). The magnetic structure is heterogeneous on a length scale larger than a few nm, as the fields produced by the copper magnetic moments decay away over this length scale. The evolution with temperature of the signals shows that, while the total amplitude remains constant, the magnetic phase begins to appear below about 15 K and gradually grows at the expense of the other as the temperature decreases (see Fig. 4). Unlike Af(T), λf is almost temperature independent. This indicates that the disorder and size of the moments immediately saturate on freezing, whereas an increasing volume fraction of the UD layer becomes magnetic as the temperature is lowered further.

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