High Pressure NQR Measurement in CeCu<sub>2</sub>Si<sub>2</sub> up to Sudden Disappearance of Superconductivity

Fujiwara, Kenji; Hata, Yoshiki; Kobayashi, Keigo; Miyoshi, Kiyotaka; Takeuchi, Jun; Shimaoka, Yoshiyuki; Kotegawa, Hisashi; Kobayashi, Tatsuo; Geibel, C.; Steglich, F.

doi:10.1143/jpsj.77.123711

Cited by 80 publications

(81 citation statements)

References 15 publications

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“…Of course, electric transport on its own constitutes only an indirect measure of the valence change. However, recent reports 21,22 based on more microscopic probes of the 4f electron count and their qualitative conclusions on a possible VCO in CeCu 2 Si 2 under p corroborate our results and assumptions. Furthermore, previous ρ data on the CeCu 2 (Si 1−x /Ge x ) 2 system (shown in Fig.…”

Section: Isothermal P-dependence and 4 F Electron Delocalizationsupporting

confidence: 91%

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Seyfarth

Rüetschi²,

Sengupta³

et al. 2012

Phys. Rev. B

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The first heavy fermion superconductor CeCu 2 Si 2 has not revealed all its striking mysteries yet. At high pressures, superconductivity is supposed to be mediated by valence fluctuations, in contrast to ambient pressure, where spin fluctuations most likely act as pairing glue. We have carried out a multiprobe (electric transport, thermopower, ac specific heat, Hall and Nernst effects) experiment up to 7 GPa on a high-quality CeCu 2 Si 2 single crystal. For the first time, the resistivity data make it possible quantitatively to draw the valence crossover line within the p-T plane and to locate the critical end point at 4.5 ± 0.2 GPa and a slightly negative temperature. In the same pressure region, remarkable features have also been detected in the other physical properties, presumably acting as further signatures of the Ce valence crossover and the associated critical fluctuations: We observe maxima in the Hall and Nernst effects and a sign change and a strong sensitivity on magnetic field in the thermopower signal.

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Section: Isothermal P-dependence and 4 F Electron Delocalizationsupporting

confidence: 91%

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Seyfarth

Rüetschi²,

Sengupta³

et al. 2012

Phys. Rev. B

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“…The superconductivity around P V was also proposed in CeIrIn 5 . The T c in CeIrIn 5 has a maximum at P = 3 GPa, which is far from the AFM quantum critical point.…”

Section: )mentioning

confidence: 80%

“…9) Therefore, the possibility of the valence fluctuation was pointed out. 9,10) However, the systematic transport measurement including Hall effect suggested the existence of the AFM spin fluctuation in CeIrIn 5 under pressure. 11) In this 115-system, weak anomalous Hall * E-mail address: araki@science.okayama-u.ac.jp effect, 12) which usually governs the temperature dependence of the Hall coefficient in heavy fermion systems, 13,14) enable the detail discussion from the Hall effect measurement.…”

Section: )mentioning

confidence: 99%

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Hall Effect in CeCu₂Si₂under Pressure

et al. 2011

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We report the results of Hall effect measurements on CeCu 2 Si 2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

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“…27 First of all, we note that the majority of low-T c superconductors, including heavy-fermion compounds, such as CeCoIn 5 , CeCu 2 Si 2 or UPd 2 Al 3 , exhibit relatively low gap ratios within ∼ 30 % of the BCS limit, according to the latest reports. 28,29 In conventional superconductors, the gap ratios remain in this narrow range (semielliptical shaded region in Fig. 1) even at higher T c , as best illustrated by Ba 1−x K x BiO 3 (T c = 30 K), [30][31][32] Rb 2 CsC 60 (T c = 33 K) 33 or MgB 2 (T c = 39 K) with its chemically substituted derivatives.…”

Section: Gap Ratiosmentioning

confidence: 96%

Crossover from weak to strong pairing in unconventional superconductors

et al. 2011

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Superconductors are classified by their pairing mechanism and the coupling strength, measured as the ratio of the energy gap, 2∆, to the critical temperature, T c . We present an extensive comparison of the 2∆/k B T c ratios among many single-and multiband superconductors from simple metals to high-T c cuprates and iron pnictides. Contrary to the recently suggested universality of this ratio in Fe-based superconductors, we find that the coupling in pnictides ranges from weak, near the BCS limit, to strong, as in cuprates, bridging the gap between these two extremes. Moreover, for Fe-and Cu-based materials, our analysis reveals a universal correlation between the gap ratio and T c , which is not found in conventional superconductors and therefore supports a common unconventional pairing mechanism in both families. An important consequence of this result for ferropnictides is that the separation in energy between the excitonic spin-resonance mode and the particle-hole continuum, which determines the resonance damping, no longer appears independent of T c .

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High Pressure NQR Measurement in CeCu₂Si₂ up to Sudden Disappearance of Superconductivity

Cited by 80 publications

References 15 publications

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Hall Effect in CeCu₂Si₂under Pressure

Crossover from weak to strong pairing in unconventional superconductors

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High Pressure NQR Measurement in CeCu2Si2 up to Sudden Disappearance of Superconductivity

Cited by 80 publications

References 15 publications

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Hall Effect in CeCu2Si2under Pressure

Crossover from weak to strong pairing in unconventional superconductors

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Product

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High Pressure NQR Measurement in CeCu₂Si₂ up to Sudden Disappearance of Superconductivity

Hall Effect in CeCu₂Si₂under Pressure