Superconductivity of Ce-based heavy fermions under pressure: Valence fluctuation mediated pairing associated with valence instability of Ce

Miyake, Kazumasa; Narikiyo, Osamu; Onishi, Yoshifumi

doi:10.1016/s0921-4526(98)00754-6

Cited by 75 publications

(62 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The low temperature of the avoided valence transition (T v ≈ 9 K) suggests the proximity of a valence quantum critical point in the pressure-temperature phase diagram of PuCoGa 5 that drives the superconductivity (12,14,30). A similar scenario has been proposed for CeCu 2 Si 2 , where one superconducting dome forms around an antiferromagnetic quantum critical point at low pressures and a second, higher-T c dome forms around a valence quantum critical point at higher pressures (13).…”

Section: Physicsmentioning

confidence: 61%

“…Because there is no evidence for PuCoGa 5 being in proximity to a magnetically ordered state (10), it is unlikely that magnetic fluctuations are the primary driver of its anomalously high T c of 18.5 K (11). Valence fluctuationswhere the total number of f electrons per ion fluctuates with the conduction band or the configuration of a fixed number of f electrons fluctuates between two or more nearly degenerate f states (sometimes known as orbital fluctuations)-have been proposed as a possible alternative mechanism for superconductivity in several heavy-fermion systems (12)(13)(14)(15). Here, we report that PuCoGa 5 's elastic moduli soften over a large temperature range above T c .…”

mentioning

confidence: 80%

See 1 more Smart Citation

Avoided valence transition in a plutonium superconductor

Ramshaw

Shekhter

McDonald

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/ itinerant duality underlies the correlated electronic states of the high-T c cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetryresolved elastic moduli of PuCoGa 5 -the highest T c superconductor of the heavy fermions (T c = 18.5 K)-and find that the bulk modulus softens anomalously over a wide range in temperature above T c . The elastic symmetry channel in which this softening occurs is characteristic of a valence instability-therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at T c , suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa 5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa 5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high T c of PuCoGa 5 .unconventional superconductivity | heavy fermions | quantum criticality | valence fluctuations | resonant ultrasound spectroscopy P uCoGa 5 enters the superconducting state below T c = 18:5 K (1)-an order of magnitude higher than all Ce-or U-based superconductors. This contrast raises the question of whether PuCoGa 5 simply benefits from a higher superconducting-pairing energy scale than its U-and Ce-based relatives or instead, whether PuCoGa 5 is host to a completely different pairing mechanism. In many lanthanide and actinide compounds, the f electrons are nearly degenerate with the conduction band. In addition, the outer f-shell states are close in energy and may support two (or more) nearly degenerate valence configurations (2). In some cases, this valence degeneracy becomes unstable, leading to valence fluctuations and ultimately, a transition to a different valence state as a function of temperature, pressure, and/or doping (3). X-ray and photoemission spectroscopy (4, 5), neutron form factor measurements (6), and theoretical calculations (7) all indicate that PuCoGa 5 is in an intermediate valence state, with the 5f 6 (Pu 2+

show abstract

Section: Physicsmentioning

confidence: 61%

mentioning

confidence: 80%

Avoided valence transition in a plutonium superconductor

Ramshaw

Shekhter

McDonald

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…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%

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

Holmes

Jaccard

Jeevan

et al. 2005

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

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 .

show abstract

“…Accordingly, superconductivity of CeIrIn 5 was proposed to be mediated by valence fluctuations rather than by spin fluctuations [16][17][18], which are more commonly taken to mediate pairing in HF superconductors (Scenario I in Fig. 1) [13,19]. However, no solid evidence of a valence instability has been revealed in CeIrIn 5 , even though nuclear quadrupolar resonance (NQR) experiments detected some differences between the two superconducting domes [17,18].…”

mentioning

confidence: 99%

“…(b) Scenario II: Two superconducting domes (SC I and SC II) develop upon increasing the lattice density [13]. SC I corresponds to Scenario I, where SC is formed via critical spin fluctuations, and SC II shows a novel superconducting state presumably arising from valence fluctuations [19].…”

mentioning

confidence: 99%

CeIrIn5: Superconductivity on a magnetic instability

et al. 2014

View full text Add to dashboard Cite

We report the doping-induced antiferromagnetic state and Fermi liquid state that are connected by a superconducting region in a series of CeIrIn5−xHgx, CeIrIn5−xSnx and CeIr1−xPtxIn5 single crystals. Measurements of the specific heat C(T ) and electrical resistivity ρ(T ) demonstrate that hole doping via Hg/In substitution gives rise to an antiferromagnetic ground state, but substitutions of In by Sn or Ir by Pt (electron doping) favor a paramagnetic Fermi liquid state. A cone-like non-Fermi liquid region is observed near CeIrIn5, showing a diverging effective mass on the slightly Hg-doped side. The obtained temperature-doping phase diagram suggests that CeIrIn5 is in proximity to an antiferromagnetic quantum critical point, and heavy fermion superconductivity in this compound is mediated by magnetic quantum fluctuations rather than by valence fluctuations.

show abstract

Superconductivity of Ce-based heavy fermions under pressure: Valence fluctuation mediated pairing associated with valence instability of Ce

Cited by 75 publications

References 8 publications

Avoided valence transition in a plutonium superconductor

Avoided valence transition in a plutonium superconductor

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure

CeIrIn5: Superconductivity on a magnetic instability

Contact Info

Product

Resources

About

Superconductivity of Ce-based heavy fermions under pressure: Valence fluctuation mediated pairing associated with valence instability of Ce

Cited by 75 publications

References 8 publications

Avoided valence transition in a plutonium superconductor

Avoided valence transition in a plutonium superconductor

Anisotropy, disorder, and superconductivity in CeCu2Si2under high pressure

CeIrIn5: Superconductivity on a magnetic instability

Contact Info

Product

Resources

About

Anisotropy, disorder, and superconductivity in CeCu₂Si₂under high pressure