Observation of Two Distinct Superconducting Phases in CeCu
            <sub>2</sub>
            Si
            <sub>2</sub>

Yuan, H. Q.; Grosche, F. M.; Deppe, M.; Geibel, C.; Sparn, G.; Steglich, F.

doi:10.1126/science.1091648

Cited by 425 publications

(375 citation statements)

References 10 publications

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“…The exact location of any atomic disorder may be highly significant, as the enhancement of impurity scattering is due to critical fluctuations [8,23] and the effect may well depend significantly on the nature and location of the impurity itself, not only at P v , but also P c . The effect of disorder on T c noted by Yuan et al [4], suggests that the initial reduction in T c with pressure in the 'low T c ' samples is due to such (possibly enhanced) impurity scattering, suppressing superconductivity between the two critical points.…”

Section: Discussionmentioning

confidence: 99%

“…The magnetically ordered state, which in pure CeCu 2 Si 2 competes with the superconducting state is thought to disappear at a magnetic quantum critical point at a small positive pressure P c of approximately 0.1GPa [6]. This quantum critical point is masked by the superconducting state in pure samples, but can be directly observed by substituting Ge for Si which leads to a suppression of superconductivity [4,7].…”

Section: Introductionmentioning

confidence: 99%

“…It has recently been proposed that a new type of superconductivity exists in the heavy fermion CeCu 2 Si 2 under high pressure [1,2,3,4,5]. In this compound, the superconducting transition temperature T c is enhanced near 3 GPa from its ambient pressure value of 0.7 K to around 2.5 K. The proposed pairing mechanism at high pressure is based on the exchange of critical valence fluctuations close to a (nearly) first order valence transition of the Ce ion at a pressure P v ≃ 4.5 GPa.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Holmes

Jaccard

Jeevan

et al. 2005

J. Phys.: Condens. Matter

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Abstract. Resistivity measurements were carried out up to 8 GPa on single crystal and polycrystalline samples of CeCu 2 Si 2 from differing sources in the homogeneity range. The anisotropic response to current direction and small uniaxial stresses was explored, taking advantage of the quasi-hydrostatic environment of the Bridgman anvil cell. It was found that both the superconducting transition temperature T c and the normal state properties are very sensitive to uniaxial stress, which leads to a shift of the valence instability pressure P v and a small but significant change in T c for different orientations with respect to the tetragonal c-axis. Coexistence of superconductivity and residual resistivity close to the Ioffe-Regel limit around 5GPa provides a compelling argument for the existence of a valence-fluctuation mediated pairing interaction at high pressure in CeCu 2 Si 2 .

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Holmes

Jaccard

Jeevan

et al. 2005

J. Phys.: Condens. Matter

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“…This means that the midpoint should actually be situated at a marginally lower p VCO . Regardless of this detail, and compared to the rather qualitative lines in previous p-T phase diagrams, [23][24][25][26] the present one is the first signature of the 4f electron delocalization based on experiment. Finally, extrapolating this line, p CeCu 2 Si 2 cr (= p V ) ∼ = 4.5 ± 0.2 GPa can be deduced, so that both coordinates of the CEP are determined within the experimental errors.…”

Section: Isothermal P-dependence and 4 F Electron Delocalizationmentioning

confidence: 98%

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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“…A major challenge to the idea of magnetically mediated superconductivity has been the dramatically different behaviour of the cerium and ytterbium heavy-fermion compounds. The cerium-based systems are often found to be superconducting [1][2][3][4][5][6] , in keeping with a magnetic pairing scenario, but corresponding ytterbium systems, or hole analogues of the cerium systems, are not. Despite searches over two decades there has been no evidence of heavy-fermion superconductivity in an ytterbium system, casting doubt on our understanding of the electron-hole parallelism between the cerium and the ytterbium compounds.…”

mentioning

confidence: 99%

Superconductivity and quantum criticality in the heavy-fermion system β-YbAlB4

et al. 2008

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A long-standing question in the field of superconductivity is whether pairing of electrons can arise in some cases as a result of magnetic interactions instead of electron-phonon-induced interactions as in the conventional Bardeen-Cooper-Schrieffer theory 1 . A major challenge to the idea of magnetically mediated superconductivity has been the dramatically different behaviour of the cerium and ytterbium heavy-fermion compounds. The cerium-based systems are often found to be superconducting 1-6 , in keeping with a magnetic pairing scenario, but corresponding ytterbium systems, or hole analogues of the cerium systems, are not. Despite searches over two decades there has been no evidence of heavy-fermion superconductivity in an ytterbium system, casting doubt on our understanding of the electron-hole parallelism between the cerium and the ytterbium compounds. Here we present the first empirical evidence that superconductivity is indeed possible in an ytterbium-based heavy-fermion system. In particular, we observe a superconducting transition at T c = 80 mK in high-purity single crystals of YbAlB 4 in the new structural β phase 7 . We also observe a novel type of non-Fermi-liquid state above T c that arises without chemical doping, in zero applied magnetic field and at ambient pressure, establishing β-YbAlB 4 as a unique system showing quantum criticality without external tuning.First we present the bulk magnetic and electronic properties of β-YbAlB 4 , a new morphology of the previously known α-YbAlB 4 (refs 7,8). Shown in Fig. 1a is the orthorhombic crystal structure of β-YbAlB 4 and the temperature dependence of the d.c. magnetic susceptibility χ = M/H. Here, M and H represent the magnetization and external field, respectively. The magnetic susceptibility shows the strong uniaxial anisotropy of an Ising system with moments aligned along the c axis. Above 100 K the c-axis susceptibility has a Curie-Weiss form χ c (T ) = C/(T − θ W ), with θ W ∼ −210 K and a Curie constant C corresponding to an effective Ising moment µ eff = g J J Z ∼ 3.1 µ B , where g J is the Landé g factor and J Z is the c-axis component of the total angular momentum. The in-plane susceptibility, on the other hand, is almost temperature independent, showing a weak peak around 200 K.Shown in Fig. 1b is the temperature dependence of the in-plane resistivity, ρ ab , along with the estimated 4f -electron contribution ρ m (defined in the figure caption), which shows a coherence peak at about 250 K. The low residual resistivity ρ ab (0) ∼ 0.4 µ cm and correspondingly high residual resistivity ratio, ρ ab (300 K)/ρ ab (0) ∼ 300, suggest that the electronic mean free path is of the order of 0.1 µm.In contrast to most other heavy-fermion compounds, the resistivity does not show a Fermi liquid (FL) regime characterized by a T 2 temperature variation (Fig. 1b). As shown in Fig. 1b insets, ρ ab is linear between 4 and 1 K and varies as T 1.5 below T 0 ∼ 1 K down to 80 mK. Below 80 mK our highest-purity samples are superconducting (Fig. 1b, insets). We shall...

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Observation of Two Distinct Superconducting Phases in CeCu ₂ Si ₂

Cited by 425 publications

References 10 publications

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Superconductivity and quantum criticality in the heavy-fermion system β-YbAlB4

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Observation of Two Distinct Superconducting Phases in CeCu 2 Si 2

Cited by 425 publications

References 10 publications

Anisotropy, disorder, and superconductivity in CeCu2Si2under high pressure

Anisotropy, disorder, and superconductivity in CeCu2Si2under high pressure

Heavy fermion superconductor CeCu2Si2under high pressure: Multiprobing the valence crossover

Superconductivity and quantum criticality in the heavy-fermion system β-YbAlB4

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Product

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Observation of Two Distinct Superconducting Phases in CeCu ₂ Si ₂

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure