An inhomogeneous Josephson phase in thin-film and high-Tc superconductors

Imry, Y.; Strongin, Myron; Homes, C. C.

doi:10.1016/j.physc.2007.08.021

Cited by 34 publications

(38 citation statements)

References 42 publications

(54 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…3), one then could have concluded that even in the insulating phase where T c = 0, the average superconducting gap still survives. Thus the observed trend of the faster decay in T c than in ∆, together with the inhomogeneous state, offers a strong support to hypothesis that the so-called "homogeneously disordered "superconducting films near SIT [1,2,8,15] can in fact be viewed as granular-like superconducting structure or Josephson phase suggested by Imry et al [3]. This, in its turn, implies that the bosonic mechanism of the superconductorto-insulator transition [29] becomes relevant.…”

Section: Shown Insupporting

confidence: 78%

“…Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in ∆, and growth of the ∆/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.PACS numbers: 74.50.+r, 74.78.Db, A pioneering idea that in the critical region of the superconductor-insulator transition (SIT) the disorderinduced inhomogeneous spatial structure of isolated superconducting droplets develops [1,2], grew into a new paradigm [3]. Extensive experimental research of critically disordered superconducting films revealed a wealth of unusual and striking phenomena, including nonmonotonic temperature and magnetic field dependence of the resistance [2,4,5,6], activated behavior of resistivity in the insulating state [1,5,6,7,8], nonmonotonic magnetic field dependence of the activation temperature, and the voltage threshold behavior [8,9,10].…”

mentioning

confidence: 99%

See 1 more Smart Citation

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

et al. 2008

View full text Add to dashboard Cite

Scanning tunneling spectroscopy at very low temperature on homogeneously disordered superconducting Titanium Nitride thin films reveals strong spatial inhomogeneities of the superconducting gap ∆ in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in ∆, and growth of the ∆/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.PACS numbers: 74.50.+r, 74.78.Db, A pioneering idea that in the critical region of the superconductor-insulator transition (SIT) the disorderinduced inhomogeneous spatial structure of isolated superconducting droplets develops [1,2], grew into a new paradigm [3]. Extensive experimental research of critically disordered superconducting films revealed a wealth of unusual and striking phenomena, including nonmonotonic temperature and magnetic field dependence of the resistance [2,4,5,6], activated behavior of resistivity in the insulating state [1,5,6,7,8], nonmonotonic magnetic field dependence of the activation temperature, and the voltage threshold behavior [8,9,10]. These features find a theoretical explanation based on the concept of disorder-induced spatial inhomogeneity in the superconducting order parameter [10,11,12,13,14]. Numerical simulations confirmed that indeed in the high-disorder regime, the homogeneously disordered superconducting film breaks up into superconducting islands separated by an insulating sea [15,16]. At the same time the direct observation of superconducting islands near the SIT justifying the fundamental but yet hypothetical concept of the disorder-induced granularity on the firm experimental foundation was still lacking.In this Letter, we report on the combined low temperature Scanning Tunneling Spectroscopy (STS) and transport measurements performed on thin Titanium Nitride films on approach to the SIT. The local tunneling density of states (LDOS) measured at 50 mK reveals disorderinduced spatial fluctuations of the superconducting gap, ∆, with both, standard deviation σ to the average gap and the gap to the critical temperature ratios, σ/∆ and ∆/T c , respectively, increasing towards the transition.Our samples were thin TiN films synthesized by atomic layer chemical vapor deposition onto a Si/SiO 2 substrate. TiN1 was a 3.6 nm thick film deposited at 400• C while TiN2 and TiN3 were 5.0 nm thick films deposited at 350 • C. TiN3 was then slightly plasma etched in order to reduce its thickness. Electron transmission images revealed that the films comprise of the densely-packed crystallites with a typical size of 4 to 6 nm. The samples were patterned into the Hall bridges using conventional UV lithography and plasma etching. It is worth noticing that identically fabricated TiN films undergo the disorder-and magnetic field-driven SIT [4,8]. Transport measurements and STS were carried out during the same run in a STM attached to a dilution refrigerator. The STM Pt/Ir t...

show abstract

Section: Shown Insupporting

confidence: 78%

mentioning

confidence: 99%

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

et al. 2008

View full text Add to dashboard Cite

show abstract

“…Below T c a weak superconducting response is observed allowing the superfluid density ρ s0 to be estimated. This material is observed to fall on the general scaling line for the cuprate superconductors, ρ s0 /8 ≃ 4.4σ dc T c [19], but in a region typically associated with the c-axis response where the superconducting response is due to Josephson coupling, suggesting that this material is indeed phase separated and constitutes a Josephson phase [20].…”

mentioning

confidence: 91%

Optical conductivity of superconducting K0.8Fe2−ySe2

Homes

Wen

et al. 2012

Phys. Rev. B

View full text Add to dashboard Cite

The optical properties of the iron-chalcogenide superconductor K0.8Fe2−ySe2 with a critical temperature Tc = 31 K have been measured over a wide frequency range in the a-b planes above and below Tc. The conductivity is incoherent at room temperature, but becomes coherent (Drude-like) at T > ∼ Tc; however, R 320 kΩ, well above the threshold for the superconductor-insulator transition at R = h/4e 2 6.9 kΩ. Below Tc, the superfluid density ρs0 48 × 10 3 cm −2 places this material on the scaling line ρs0/8 4.4 σ dc Tc, but in a region associated with Josephson coupling, suggesting this material is inhomogeneous and constitutes a Josephson phase.

show abstract

“…However, as the electronic doping is increased the material becomes more homogeneous, the size of the superconducting regions increases and the "granularity" is reduced, allowing the system to revert to a more conventional behavior. It should be noted that in this "large-grain" picture, the Uemura relation is expected to be recovered, 37 suggesting that this is a reasonable description of the moderately-underdoped region.…”

Section: Fig 2: (Color Online)mentioning

confidence: 83%

“…35 We speculate that the severely-underdoped materials are electronically segregated into superconducting hole-rich regions, and holepoor regions that form a poorly-conducting barrier region. If the "granularity" of such a system is fine enough, then the superconducting regions will be linked through the Josephson effect, 36 in essence forming a Josephson phase, 37 and in fact it has recently been demonstrated that the scaling relation observed here can be derived for a two-dimensional Josephson array. 38 Within this framework the doping level may in principle be reduced to such an extent that Josephson coupling between the superconducting regions is no longer possible.…”

Section: Fig 2: (Color Online)mentioning

confidence: 85%

Scaling of the superfluid density in strongly underdopedYBa2Cu3O6+y: Evidence for a Josephson phase

Homes

2009

Phys. Rev. B

View full text Add to dashboard Cite

Recent measurements on extremely-underdoped YBa2Cu3O6+y [Phys. Rev. Lett. 99, 237003 (2007)] have allowed the critical temperature Tc, superfluid density ρs0 ≡ ρs(T ≪ Tc) and dc conductivity σ dc (T Tc) to be determined for a series of electronic dopings for Tc ≃ 3 − 17 K. The general scaling relation ρs0/8 ≃ 4.4 σ dc Tc is observed, extending the validity of both the ab-plane and c-axis scaling an order of magnitude and creating a region of overlap for the first time. This suggests that severely underdoped materials may constitute a Josephson phase; as the electronic doping is increased a more uniform superconducting state emerges.PACS numbers: 89.75. Da,74.72.Bk,74.25.Gz,74.25.Nf Since the discovery of superconductivity at elevated temperatures in the cuprate materials, there has been a concerted effort to identify empirical scaling relations in the hope of providing insights to the mechanism for superconductivity in these materials. While the nature of the superconductivity remains elusive, it is now generally accepted that in the optimally-doped compounds the superconducting energy gap has a d-wave symmetry. Much of the current research in the cuprate materials focuses on the underdoped compounds where the development of a pseudogap 1 in the antinodal region in the normal state at a characteristic temperature T * leads to the formation of Fermi arcs (or pockets) centered around the nodal regions. 2,3 There is currently a considerable amount of debate as to whether or not the pseudogap represents preformed pairs that simply lack the coherence required for superconductivity, 3 or if superconductivity originates in the Fermi arcs (pockets) and the pseudogap reflects some alternative ground state that competes with superconductivity. 4,5,6 An important scaling relation in the underdoped cuprates is the Uemura relation, 7,8 which notes that the superfluid density at low temperature (ρ s0 ) is proportional to the critical temperature (T c ). The superfluid density is defined here as ρ s0 ≡ 1/λ 2 0 , where λ 0 = λ(T ≪ T c ) is the effective penetration depth. Alternatively, ρ s0 is also referred to as the superfluid stiffness where ρ s0 = 4πn s0 e 2 /m * c 2 , where n s0 is the density of the superconducting carriers and m * is an effective mass. The Uemura relation works well over much of the underdoped region, but does not apply in optimal and overdoped materials. 9 In addition, as the phase diagram for YBa 2 Cu 3 O 6+y has been extended to the severely underdoped regime, 10 the scaling of ρ s0 is observed to change from a linear to power-law relation. 11,12,13,14 In this work we demonstrate that the severelyunderdoped data for YBa 2 Cu 3 O 6+y is in fact consistent with a more general scaling relation ρ s0 /8 ≃ 4.4 σ dc T c where σ dc is the dc conductivity measured at T T c (note that in this representation both σ dc and T c are shown in units of cm −1 , so that the constant is dimensionless and ρ s0 has the units of cm −2 ). 15,16,17 In the cuprates this scaling relation is valid for the copperoxygen plane...

show abstract

An inhomogeneous Josephson phase in thin-film and high-Tc superconductors

Cited by 34 publications

References 42 publications

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Optical conductivity of superconducting K0.8Fe2−ySe2

Scaling of the superfluid density in strongly underdopedYBa2Cu3O6+y: Evidence for a Josephson phase

Contact Info

Product

Resources

About