Tunneling and magnetic characteristics of superconducting<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">ZrB</mml:mi></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>single crystals

Tsindlekht, M. I.; Leviev, G. I.; Asulin, Itay; Sharoni, Amos; Millo, Oded; Felner, I.; Paderno, Yu. B.; Филиппов, В. Б.; Belogolovskii, Mikhail

doi:10.1103/physrevb.69.212508

Cited by 50 publications

(74 citation statements)

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“…(5) gives T c = 6.09(2) K, λ −2 (0) = 47.4(2) nm, and ∆ 0 = 1.251(9) meV. The ratio 2∆ 0 /k B T c = 4.77 (4) [6]. It was explained by enhanced surface characteristics of the ZrB 12 leading to rather different superconducting properties of bulk [4,6,26] and surface [3,6,27,28].…”

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confidence: 85%

“…It was explained by enhanced surface characteristics of the ZrB 12 leading to rather different superconducting properties of bulk [4,6,26] and surface [3,6,27,28]. Our measurements were performed in the Meissner state, with the field penetrating on a distance λ from the surface and, therefore, give a value of the superconducting gap consistent with those one reported in the surface sensitive experiments [3,6]. To estimate the uncertainty in the absolute value of λ(0) we used a procedure similar to that one described in Refs.…”

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confidence: 99%

“…The ratio 2∆ 0 /k B T c = 4.79(1) is found to be pressure independent and close to the strong coupling BCS value 4.8(1) reported in Refs. [3,6]. The value of λ extrapolated to zero temperature and at p = 0 was estimated to be 140(30) nm.…”

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Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

et al. 2005

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Magnetization measurements under hydrostatic pressure up to 10.5 kbar in zirconium dodecaboride ZrB12 superconductor (Tc ≃ 6.0 K at p = 0) were carried out. A negative pressure effect on Tc with dTc/dp = −0.0225(3) K/kbar was observed. The electron-phonon coupling constant λ el−ph decreases with increasing pressure with d ln λ el−ph /dp ≃ −0.20%/kbar. The magnetic field penetration depth λ was studied in the Meissner state and, therefore, probes only the surface of the sample. The absolute values of λ and the superconducting energy gap at ambient pressure and zero temperature were found to be λ(0) =140(30) nm and ∆0 =1.251(9) meV, respectively. ∆0 scales linearly with Tc as 2∆0/kBTc = 4.79(1). The studies of the pressure effect on λ reveal that λ −2 increases with pressure with d ln λ −2 (0)/dp = 0.60(23) %/kbar. This effect can not be explained within the framework of conventional adiabatic electron-phonon pairing, suggesting that close to the surface, an unconventional non-adiabatic character of the electron-phonon coupling takes place.PACS numbers: 74.70. Ad, 74.62.Fj, 74.25.Ha, 83.80.Fg The traditional concept of superconductivity is strictly associated with the electron-phonon interaction. The conventional theory is based on the Migdal-Eliashberg adiabatic approximation [1] that, in fact, leads to the prediction of many peculiar features which are a direct evidence of a phonon mediated superconductivity. The adiabatic approximation is valid if the parameter ω 0 /E f is small (ω 0 is the relevant phonon frequency and E f is the Fermi energy). Usually this parameter is regarded as a measure of nonadibaticity. However, crossover from a conventional adiabatic to an unconventional nonadiabatic regime does not depend only on the value of the ω 0 /E f ratio. Paci et al. [8] show that even in a case of small "adiabatic" ratio one would expect the nonadiabatic coupling in superconductors having high value of the electron-phonon coupling constant λ el−ph . Among BCS superconductors the zirconium dodecaboride (ZrB 12 ) is probably a candidate for the observation of such type of anomalous coupling. It stems from the rather small value of the Fermi energy ∼1 eV [3] that, together with the Debye temperature ∼20 meV [4], leads to a ratio ω 0 /E f ∼0.02. A strong coupling ratio 2∆/k B T c ≃ 4.8 was observed by surface sensitive techniques [3,6]. This suggests that the electron-phonon coupling constant, which has a bulk value λ el−ph ≃ 0.67 [3], increases at the surface. From the comparison with strong coupled metallic superconductors [7] one would expect λ surf.el−ph ≃ 1.7 − 1.9. Moreover, it was pointed out by Cappelluti et al.[2] that nonadiabatic character can be further enhanced by low charge carrier density, that is the case for ZrB 12 [4,5].One of the key feature of nonadiabatic superconductivity is the observation of unconventional isotope and pressure effects on the magnetic field penetration depth λ. Note, that in adiabatic superconductors (or in the superconductors where the nonadiabatic effects are small) the...

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Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

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“…33 For ZrB 12 , an electron-phonon coupling constant Х 1 was extracted in this way, in agreement with previous reports. [34][35][36] Figure 8 shows a comparison at low temperature of the low-frequency part of the reflectivity for the two compounds. The fits, including the contribution from the electron-phonon interaction as described above, are presented by a solid red line.…”

Section: ͑1͒mentioning

confidence: 99%

Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12
Teyssier
¹
,
Lortz
²
,
Petrović
³

et al. 2008
Phys. Rev. B
46
4
41
0
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We report a detailed study of specific heat, electrical resistivity, and optical spectroscopy in the superconducting boride LuB 12 ͑T c = 0.4 K͒, and compare it to the higher T c compound ZrB 12 ͑T c =6 K͒. Both compounds have the same structure based on enclosed metallic Lu or Zr ions in oversized boron cages. The infrared reflectivity and ellipsometry in the visible range allow us to extract the optical conductivity from 6 meV to 4 eV in the normal state from 20 to 280 K. By extracting the superconducting properties, phonon density of states, and electron-phonon coupling function from these measurements, we discuss the important factors governing T c and explain the difference between the two compounds. The phonon density of states seems to be insignificantly modified by substitution of Zr with Lu. However, the soft vibrations of the metal ions in boron cages, responsible for the relatively high T c in ZrB 12 , have almost no contribution to the electron-phonon coupling in LuB 12 .

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“…5 Scanning tunneling spectroscopy and magnetization measurements show that ZrB 12 single crystal has excellent surface properties. 6 Enthalpy measurements 7 in Zr 0:6 Y 0:4 B 12 suggest the most probable valence state of Zr to be (þ4). In contrast, the x-ray photoemission (XP) spectroscopic measurements on polycrystalline ZrB 12 sample indicate neutral state of Zr; the earlier observation of (þ4) valence state is attributed to the impurity phase.…”

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Surface bulk differences in a conventional superconductor, ZrB12

Thakur

Biswas

Sahadev

et al. 2013

Journal of Applied Physics

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We studied the electronic structure of a conventional superconductor, ZrB 12 , using high resolution x-ray photoemission spectroscopy and single crystalline samples. Experimental results with different bulk sensitivity reveal boron deficiency at the surface while the bulk is stoichiometric and different valence states of Zr at the surface relative to those in the bulk. Signature of satellite features is observed in the Zr core level spectra corresponding to the bulk of the material suggesting importance of electron correlation among the conduction electrons in the bulk while the surface appears to be uncorrelated. These results provide an insight on surface-bulk differences, which is important for fabrication of devices based on such superconductors. V C 2013 AIP Publishing LLC.

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Tunneling and magnetic characteristics of superconductingZrB12single crystals

Cited by 50 publications

References 18 publications

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12
Teyssier
¹
,
Lortz
²
,
Petrović
³

et al. 2008
Phys. Rev. B
46
4
41
0
View full text Add to dashboard Cite

Surface bulk differences in a conventional superconductor, ZrB12

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Tunneling and magnetic characteristics of superconductingZrB12single crystals

Cited by 50 publications

References 18 publications

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12Teyssier1, Lortz2, Petrović3 et al. 2008Phys. Rev. B464410View full textAdd to dashboardCite

Surface bulk differences in a conventional superconductor, ZrB12

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Resources

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Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12
Teyssier
¹
,
Lortz
²
,
Petrović
³

et al. 2008
Phys. Rev. B
46
4
41
0
View full text Add to dashboard Cite