Boron Isotope Effect in Superconducting Zirconium Dodecaboride

Chu, C. W.; Hill, H.H.

doi:10.1126/science.159.3820.1227

Cited by 21 publications

(13 citation statements)

References 8 publications

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“…To emphasize the variation of ρ(T) in a superconductive state, we plot these data in the inset. The transition temperature (T c0 =6.0 K) is consistent with the previously reported values for ZrB 12 (6.03 K) [11,13] and is larger than that of ZrB 2 polycrystalline samples (5.5 K) [2]. The ZrB 12 samples demonstrate a remarkably narrow transition with ∆T=0.04 K. We believe that such narrow transition is indicator of the good quality of our samples.…”

Section: Fig2 Etching Pattern Of a Zrbsupporting

confidence: 91%

“…It was suggested [3] that the superconductivity in YB 6 and ZrB 12 (T c of 6.5-7.1 K and 6.03 K, respectively [3]) is exactly due to the effect of a cluster of light boron atoms. At the same time, a much smaller isotope effect on T c for boron in comparison with Zr isotopic substitution suggests that the boron in ZrB 12 serves as inert background for the Zr-driven superconductivity [13,14]. Clearly systematic study of ZrB 12 is needed to address the question of superconductivity in this compound.…”

Section: Introductionmentioning

confidence: 99%

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Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

2006

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We report the measurements of the temperature dependence of the resistivity, ρ(T), magnetic penetration depth, λ(T) the lower, H c1 (T), and upper, H c2 (T), critical magnetic fields, for single crystals of dodecaboride ZrB 12 , diboride ZrB 2 and thin films of diboride MgB 2 . We observe a number of deviations from conventional behavior in these materials. Although ZrB 12 behaves like a simple metal in the normal state, the resistive Debye temperature, 300 K, is three times smaller relative to that (800-1200 K) calculated from the specific heat, C(T), data. We observe predominantly quadratic temperature behavior of resistivity in ZrB 12 below 25 K, and in ZrB 2 below 100 K, indicating the possible importance of the electron-electron interaction in these borides. Superfluid density of ZrB 12 displays unconventional temperature dependence with pronounced shoulder at T/T c equal to 0.65. Contrary to conventional theories we found a linear temperature dependence of H c2 (T) for ZrB 12 from T c down to 0.35 K. We suggest that both λ(T) and H c2 (T) dependencies in ZrB 12 can be explained by two band BCS model with different superconducting gap and T c .

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Section: Fig2 Etching Pattern Of a Zrbsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

2006

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“…7 Since large high-quality single crystals are available, the superconductivity in ZrB 12 and YB 6 has been object of intense research. The isotope effect in ZrB 12 for zirconium 15 ͑␤ Ϸ −0.32͒ is much larger than for boron 16 ͑␤ Ϸ −0.09͒, pointing to a large contribution of lattice modes involving Zr atoms to the electron-phonon coupling responsible for superconductivity in ZrB 12 . The same was concluded from an inversion of specific-heat and resistivity data for YB 6 ͑Ref.…”

Section: Introductionmentioning

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
47
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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“…It was suggested that the superconductivity in YB 6 and ZrB 12 (having highest T c of 6.5 − 7.1 K and 6.03 K, respectively [3]), might be due to the hypothetical cubic metallic boron. However, a much smaller isotope effect on T c for boron in comparison with Zr isotopic substitution suggests that the boron in ZrB 12 serves as inert background, and this is Zr that actually is critical for superconductivity [11,12], even though ZrB 12 chemically contains mainly boron.…”

Section: Introductionmentioning

confidence: 99%

Electron transport, penetration depth, and the upper critical magnetic field in ZrB12 and MgB2

Gasparov

Sidorov

Зверькова

et al. 2005

J. Exp. Theor. Phys.

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We report on the synthesis and measurements of the temperature dependence of resistivity, ρ(T ), the penetration depth, λ(T ), and upper critical magnetic field, Hc2(T ), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Grüneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR = 280 K, for ZrB12 (as compared to MgB2 with TR = 900 K). The ρ(T ) and λ(T ) dependencies of these samples reveal a superconducting transition of ZrB12 at Tc = 6.0 K. Although a clear exponential λ(T ) dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2∆(0)/kBTc = 1.6 for MgB2 films and pellets, in good agreement with published data for 3D π -sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T ) (Hc2(0) = 0.15 T ) for ZrB12.

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Boron Isotope Effect in Superconducting Zirconium Dodecaboride

Abstract: The boron isotope effect in ZrB(12) has been determined to be T(c) infinity M(alpha), where alpha is equal to - 0.09 +/- 0.05, M is the boron mass, and T(c) is the supercondiucting transition temperature.

Cited by 21 publications

References 8 publications

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

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
47
4
41
0
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Electron transport, penetration depth, and the upper critical magnetic field in ZrB12 and MgB2

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Boron Isotope Effect in Superconducting Zirconium Dodecaboride

Abstract: The boron isotope effect in ZrB(12) has been determined to be T(c) infinity M(alpha), where alpha is equal to - 0.09 +/- 0.05, M is the boron mass, and T(c) is the supercondiucting transition temperature.

Cited by 21 publications

References 8 publications

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

Two-gap superconductivity inZrB12: Temperature dependence of critical magnetic fields in single crystals

Effect of electron-phonon coupling on the superconducting transition temperature in dodecaboride superconductors: A comparison ofLuB12withZrB12Teyssier1, Lortz2, Petrović3 et al. 2008Phys. Rev. B474410View full textAdd to dashboardCite

Electron transport, penetration depth, and the upper critical magnetic field in ZrB12 and MgB2

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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
47
4
41
0
View full text Add to dashboard Cite