Angular dependence of tunneling effects in Ba 1-x K x BiO 3 grain boundaries

Kussmaul, A.; Hellman, E. S.; Hartford, E. H.; Gupta, Arunava; Tedrow, Prabha K.

doi:10.1117/12.182679

Cited by 2 publications

(1 citation statement)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As is well known [603], this peak is caused by tunneling of thermally excited quasiparticles between empty states with an enhanced DOS located above and below equal superconducting gaps in symmetric S-I-S junctions. Such a feature was found, for example, in G s (V ) measured for grainboundary symmetric tunnel junctions in epitaxial films of the s-wave oxide CDWS Ba 1−x K x BiO 3 [616]. One should be careful not to confuse this peak with the dc Josephson peak restricted to V = 0, which is often seen for symmetric high-T c junctions [399].…”

Section: Dip-hump Structures and Pseudogaps In Tunnel Current-voltagementioning

confidence: 84%

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Gabovich

Войтенко

Ekino

et al. 2010

Advances in Condensed Matter Physics

View full text Add to dashboard Cite

Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.

show abstract

Section: Dip-hump Structures and Pseudogaps In Tunnel Current-voltagementioning

confidence: 84%

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Gabovich

Войтенко

Ekino

et al. 2010

Advances in Condensed Matter Physics

View full text Add to dashboard Cite

show abstract

Evidence for two-particle normal-state tunneling inBa1−xK<

Hellman

1995

Phys. Rev. B

View full text Add to dashboard Cite

The asymmetric background conductance linear in bias voltage usually observed in Bal "KBi03 superconductor-insulator-normal (SIN) tunnel junctions is associated with a zero-bias conductance linear in temperature above the superconducting transition. The ratio of the temperature coefficient and the voltage coefficient provides insight into the mechanism causing the linear background conductance.We present a simple model involving tunnehng through two-particle states (negative-U, bipolaron) in the barrier that explains the linear background, the asymmetry, and the linear temperature dependence of the conductance. Measurements of native-barrier Bal K Bi03 tunnel junctions are in quantitative agreement with the model. Since its discovery, Ba, K"Bi03 (0.4 (x (Q.5) (BKBO) (Refs. 1 and 2) has been considered a useful point of comparison to the high-T, cuprate superconductors. Unlike the cuprates, BKBO and its close relatives, Ba, "RbBi03 and BaPb, Bi O3, are known to have a clean gap in tunneling with 2A/kz T, =3. 5, consistent with weak-to-moderate coupling BCS theory. From the isotope shift, inelastic neutron scattering, ' tunneling spectra, ' '" and the normal-state properties, ' it is generally accepted that electron-phonon coupling plays at least a partial role in the superconductivity. The cubic structure and lack of magnetic ions further simplify the theory of superconductivity in BKBO. On the other hand, the high-T, (up to 31 K), especially given the low electronic density of states N*, suggests that a deeper physical understanding of BKBO will be relevant to understanding other high-T, materials. Particularly intriguing are the analogous electronic phase diagrams in the cuprate and bismuthate systems. High-temperature superconducting states in both systems are proximate to collective-mode insulator states (the charge-density-wave semiconductor in BaBi03 and the antiferromagnetic insulator in the cuprates). A disordered or glassy state, characterized by variable-range-hopping conductivity, ' lies in between.Perhaps the most striking similarly between the bismuthate and cuprate superconductors is the asymmetric linear background conductance seen in tunnel junctions. ' Even though the linear background has been most widely discussed in the context of YBa2Cu307 etched-surface junctions, BizSr2CaCu208 cleaved surface junctions, and Bi2Sr2CaCu208 point-contact junctions, the phenomenon appears to be even more robust in the bismuthate systems. The apparent differences between tunneling perpendicular to and along copper oxygen planes have led to explanations for the linear background conductance that depend on the strong anisotropy of the cuprates, thus ignoring the similar phenomena in the cubic bismuthates. There are several important differences between the linear backgrounds in cuprate junctions and in bismuthate junctions. One is the sign of the asymmetry: in bismuthate junctions, the conductance is always higher with the metal electrode negatively biased, while for cuprates, the conductance is always higher wit...

show abstract

Angular dependence of tunneling effects in Ba 1-x K x BiO 3 grain boundaries

Cited by 2 publications

References 0 publications

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Evidence for two-particle normal-state tunneling inBa1−xK<

Contact Info

Product

Resources

About