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Controlling the near-surface superfluid density in underdoped YBa2Cu3O(6+x) by photo-illumination.

Stilp E, Suter A, Prokscha T, Salman Z, Morenzoni E, Keller H, Pahlke P, Hühne R, Bernhard C, Liang R, Hardy WN, Bonn DA, Baglo JC, Kiefl RF - Sci Rep (2014)

Bottom Line: Furthermore, systematic investigations in underdoped YBa2Cu3O(6+x) (YBCO) have shown an enhanced critical temperature Tc.Until now, studies of photo-persistent conductivity (PPC) have been limited to investigations of structural and transport properties, as well as the onset of superconductivity.Here we show how changes in the magnetic screening profile of YBCO in the Meissner state due to PPC can be determined on a nanometer scale utilizing low-energy muons.

View Article: PubMed Central - PubMed

Affiliation: 1] Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland [2] Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.

ABSTRACT
The interaction with light weakens the superconducting ground state in classical superconductors. The situation in cuprate superconductors is more complicated: illumination increases the charge carrier density, a photo-induced effect that persists below room temperature. Furthermore, systematic investigations in underdoped YBa2Cu3O(6+x) (YBCO) have shown an enhanced critical temperature Tc. Until now, studies of photo-persistent conductivity (PPC) have been limited to investigations of structural and transport properties, as well as the onset of superconductivity. Here we show how changes in the magnetic screening profile of YBCO in the Meissner state due to PPC can be determined on a nanometer scale utilizing low-energy muons. The data obtained reveal a strongly increased superfluid density within the first few tens of nanometers from the sample surface. Our findings suggest a non-trivial modification of the near-surface band structure and give direct evidence that the superfluid density of YBCO can be controlled by light illumination.

No MeSH data available.


Related in: MedlinePlus

Schematic diagram of the experimental µSR process cycle.Left panel: After zero field cooling (ZFC) the sample an external magnetic field  was applied within the ab-plane. The interface to the vacuum is labeled with z = 0. The screened magnetic field values B at different depths z along the crystallographic c axis were determined via the Larmor frequency of the implanted positively charged muons (red circles) ωL = γµB at 10 K for the YBCO thin films and at 5 K for the YBCO ortho-VIII single crystals. The muon spin precesses at ωL around the local magnetic field B present in the sample. The Larmor frequency ωL is extracted from the muon-spin polarization function P(t) measured via the decay positron. Center panel: The LE-µSR measurements were followed by the in-situ photo illumination of the samples for ~ 3 days (4 – 5 · 1022 photons/cm2) at 270 K with a high-intensity LED source. Right panel: Afterwards the samples were ZFC to 10 K/5 K, repeating the measurement of the screened magnetic field profile as described above. To return the YBCO system to its initial state it was kept above room temperature for about one day. The resistance measurements have been performed under comparable conditions (see supplementary section S1).
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f3: Schematic diagram of the experimental µSR process cycle.Left panel: After zero field cooling (ZFC) the sample an external magnetic field was applied within the ab-plane. The interface to the vacuum is labeled with z = 0. The screened magnetic field values B at different depths z along the crystallographic c axis were determined via the Larmor frequency of the implanted positively charged muons (red circles) ωL = γµB at 10 K for the YBCO thin films and at 5 K for the YBCO ortho-VIII single crystals. The muon spin precesses at ωL around the local magnetic field B present in the sample. The Larmor frequency ωL is extracted from the muon-spin polarization function P(t) measured via the decay positron. Center panel: The LE-µSR measurements were followed by the in-situ photo illumination of the samples for ~ 3 days (4 – 5 · 1022 photons/cm2) at 270 K with a high-intensity LED source. Right panel: Afterwards the samples were ZFC to 10 K/5 K, repeating the measurement of the screened magnetic field profile as described above. To return the YBCO system to its initial state it was kept above room temperature for about one day. The resistance measurements have been performed under comparable conditions (see supplementary section S1).

Mentions: LE-µSR is an unique and powerful technique to measure non-trivial B(z) on a nanometer scale in a wide variety of superconducting single crystals18, thin films1920, and heterostructures2122, allowing also the observation of non-local effects232425. Positively charged muons are slowed down and implanted into the samples at different mean implantation depths (Figs. 2 and 3). The Larmor frequency of the muons, ωL(z), directly related to the local magnetic field B at the muon stopping site (ωL = γµB with the muon gyromagnetic moment γµ = 2π · 135.5 MHz/T), is measured via the decay positron. For a semi-infinite sample, the London equation yields a magnetic penetration profile B (z) = Bext · exp (−z/λL), for the boundary condition B(z = 0) = Bext. Therefore, measuring B (z) allows one to determine the magnetic penetration depth λL and thereby the superfluid density 26. The process cycle and the conditions of the LE-µSR measurements are presented schematically in Fig. 3. The in-situ illumination setup is described in detail in the supplementary section S1.


Controlling the near-surface superfluid density in underdoped YBa2Cu3O(6+x) by photo-illumination.

Stilp E, Suter A, Prokscha T, Salman Z, Morenzoni E, Keller H, Pahlke P, Hühne R, Bernhard C, Liang R, Hardy WN, Bonn DA, Baglo JC, Kiefl RF - Sci Rep (2014)

Schematic diagram of the experimental µSR process cycle.Left panel: After zero field cooling (ZFC) the sample an external magnetic field  was applied within the ab-plane. The interface to the vacuum is labeled with z = 0. The screened magnetic field values B at different depths z along the crystallographic c axis were determined via the Larmor frequency of the implanted positively charged muons (red circles) ωL = γµB at 10 K for the YBCO thin films and at 5 K for the YBCO ortho-VIII single crystals. The muon spin precesses at ωL around the local magnetic field B present in the sample. The Larmor frequency ωL is extracted from the muon-spin polarization function P(t) measured via the decay positron. Center panel: The LE-µSR measurements were followed by the in-situ photo illumination of the samples for ~ 3 days (4 – 5 · 1022 photons/cm2) at 270 K with a high-intensity LED source. Right panel: Afterwards the samples were ZFC to 10 K/5 K, repeating the measurement of the screened magnetic field profile as described above. To return the YBCO system to its initial state it was kept above room temperature for about one day. The resistance measurements have been performed under comparable conditions (see supplementary section S1).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150113&req=5

f3: Schematic diagram of the experimental µSR process cycle.Left panel: After zero field cooling (ZFC) the sample an external magnetic field was applied within the ab-plane. The interface to the vacuum is labeled with z = 0. The screened magnetic field values B at different depths z along the crystallographic c axis were determined via the Larmor frequency of the implanted positively charged muons (red circles) ωL = γµB at 10 K for the YBCO thin films and at 5 K for the YBCO ortho-VIII single crystals. The muon spin precesses at ωL around the local magnetic field B present in the sample. The Larmor frequency ωL is extracted from the muon-spin polarization function P(t) measured via the decay positron. Center panel: The LE-µSR measurements were followed by the in-situ photo illumination of the samples for ~ 3 days (4 – 5 · 1022 photons/cm2) at 270 K with a high-intensity LED source. Right panel: Afterwards the samples were ZFC to 10 K/5 K, repeating the measurement of the screened magnetic field profile as described above. To return the YBCO system to its initial state it was kept above room temperature for about one day. The resistance measurements have been performed under comparable conditions (see supplementary section S1).
Mentions: LE-µSR is an unique and powerful technique to measure non-trivial B(z) on a nanometer scale in a wide variety of superconducting single crystals18, thin films1920, and heterostructures2122, allowing also the observation of non-local effects232425. Positively charged muons are slowed down and implanted into the samples at different mean implantation depths (Figs. 2 and 3). The Larmor frequency of the muons, ωL(z), directly related to the local magnetic field B at the muon stopping site (ωL = γµB with the muon gyromagnetic moment γµ = 2π · 135.5 MHz/T), is measured via the decay positron. For a semi-infinite sample, the London equation yields a magnetic penetration profile B (z) = Bext · exp (−z/λL), for the boundary condition B(z = 0) = Bext. Therefore, measuring B (z) allows one to determine the magnetic penetration depth λL and thereby the superfluid density 26. The process cycle and the conditions of the LE-µSR measurements are presented schematically in Fig. 3. The in-situ illumination setup is described in detail in the supplementary section S1.

Bottom Line: Furthermore, systematic investigations in underdoped YBa2Cu3O(6+x) (YBCO) have shown an enhanced critical temperature Tc.Until now, studies of photo-persistent conductivity (PPC) have been limited to investigations of structural and transport properties, as well as the onset of superconductivity.Here we show how changes in the magnetic screening profile of YBCO in the Meissner state due to PPC can be determined on a nanometer scale utilizing low-energy muons.

View Article: PubMed Central - PubMed

Affiliation: 1] Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland [2] Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.

ABSTRACT
The interaction with light weakens the superconducting ground state in classical superconductors. The situation in cuprate superconductors is more complicated: illumination increases the charge carrier density, a photo-induced effect that persists below room temperature. Furthermore, systematic investigations in underdoped YBa2Cu3O(6+x) (YBCO) have shown an enhanced critical temperature Tc. Until now, studies of photo-persistent conductivity (PPC) have been limited to investigations of structural and transport properties, as well as the onset of superconductivity. Here we show how changes in the magnetic screening profile of YBCO in the Meissner state due to PPC can be determined on a nanometer scale utilizing low-energy muons. The data obtained reveal a strongly increased superfluid density within the first few tens of nanometers from the sample surface. Our findings suggest a non-trivial modification of the near-surface band structure and give direct evidence that the superfluid density of YBCO can be controlled by light illumination.

No MeSH data available.


Related in: MedlinePlus