The heavy-fermion superconductor UPd<sub>2</sub>Al<sub>3</sub>at very high pressure

Link, P.; Jaccard, D.; Geibel, C.; Wassilew, C.; Steglich, F.

doi:10.1088/0953-8984/7/2/015

Cited by 13 publications

(18 citation statements)

References 9 publications

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“…However, there are some striking differences between the spectrum observed in CeCu 2 Si 2 and those seen in the other superconductors. In contrast to CeCu 2 Si 2 , where SC and long-range AF order exclude each other, SC in UPd 2 Al 3 occurs inside the antiferromagnetically ordered part of its magnetic phase diagram, which is far away from any QCP 35 . Whether a QCP underlies SC in the cuprates, the iron pnictides, or CeCoIn 5 , is yet to be established.…”

Section: Comparison With Other Unconventional Superconductorsmentioning

confidence: 83%

Magnetically driven superconductivity in CeCu2Si2

Stockert¹,

Arndt²,

et al. 2010

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PACS numbers: * Electronic address: stockert@cpfs.mpg.de 1The origin of unconventional superconductivity, including high-temperature and heavy-fermion superconductivity, is still a matter of controversy. Spin excitations instead of phonons are thought to be responsible for the formation of Cooper pairs. Using inelastic neutron scattering, we present the first in-depth study of the magnetic excitation spectrum in momentum and energy space in the superconducting and the normal states of CeCu 2 Si 2 . A clear spin excitation gap is observed in the superconducting state. We determine a lowering of the magnetic exchange energy in the superconducting state, in an amount considerably larger than the superconducting condensation energy. Our findings identify the antiferromagnetic excitations as the major driving force for superconducting pairing in this prototypical heavy-fermion compound located near an antiferromagnetic quantum critical point.While conventional superconductivity (SC) is generally incompatible with magnetism, magnetic excitations seem to play an important role in the Cooper pair formation of unconventional superconductors such as the high-T c cuprates or the low-T c organic and heavyfermion (HF) superconductors. Since the discovery of SC in CeCu 2 Si 2 1 , antiferromagnetic (AF) spin excitations have been proposed as a viable mechanism for SC 2-4 . The discovery of SC at the boundary of AF order in CePd 2 Si 2 5 has pushed this notion into the framework of AF quantum criticality 6 . Unfortunately, such quantum critical points (QCPs) proximate to HF superconductors typically arise under pressure, which makes it difficult to probe their magnetic excitation spectrum.Here, we report a detailed study of the magnetic excitations in CeCu 2 Si 2 , which exhibits SC below T c ≈ 0.6 K. This prototypical HF compound is ideally suited for our purpose, since SC here is in proximity to an AF QCP already at ambient pressure (cf. Fig. 1(a)).As displayed in Fig. 1(b) CeCu 2 Si 2 crystallises in a structure with body-centred tetragonal symmetry and is one of the best studied HF superconductors and well characterised by low-temperature transport and thermodynamic measurements 7 . Moreover, those measurements in the field-induced normal state have already provided evidence that the QCP in this compound is of the three-dimensional (3D) spin-density-wave (SDW) type 8 . The spatial anisotropy of the spin fluctuations in superconducting CeCu 2 Si 2 was measured at T = 0.06 K and at an energy transfer ω = 0.2 meV and is shown in Fig. 1(c). These magnetic correlations display only a small anisotropy (a factor of 1.5) in the correlation lengths 2 between the [110] and the [001] direction. Therefore, these quite isotropic spin fluctuations are in line with thermodynamic and transport measurements exhibiting C/T = γ 0 − a √ T or ρ − ρ 0 = AT α , α = 1 − 1.5 8,9 , and strongly support a three-dimensional quantum critical SDW scenario 10 . We are able to identify the magnetic excitations in the normal state of paramagnetic, ...

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Section: Comparison With Other Unconventional Superconductorsmentioning

confidence: 83%

Magnetically driven superconductivity in CeCu2Si2

Stockert¹,

Arndt²,

et al. 2010

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“…The electrical resistivity under pressure shows that T N decreases from 14 K to about 8 K at a pressure of 65 kbar, while the normal state maximum in the resistivity increases (Link et al, 1995). At low pressures elastic neutron scattering shows an initial increase of µ ord , followed by a decrease above 5 kbar with a rate dµ ord /dp = −016 µ B /kbar.…”

Section: A Upd2al3mentioning

confidence: 94%

“…For instance, (i) the thermal expansion, which shows a large sensitivity to uniaxial stress (Link et al, 1995), (ii) the longitudinal and transverse elastic constants , (iii) a kink in the 27 Al spin-lattice relaxation rate and a gradual increase of the 27 Al NMR line width (Kyogaku et al, 1993), (iv) the emergence of a gap in tunneling spectroscopy (Aarts et al, 1994), and (v) an increase of the thermal conductivity (Hiroi et al, 1997).…”

Section: A Upd2al3mentioning

confidence: 99%

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Superconducting phases off-electron compounds

2009

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Intermetallic compounds containing f-electron elements display a wealth of superconducting phases, that are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferro-and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconductivity near valence transitions, or in the vicinity of magneto-polar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of f-electron compounds is reviewed.

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“…The response of superconductivity in these compounds to applied pressure differ. In UPd 2 Al 3 , T c remains nearly unchanged for applied pressures up to 6.5 GPa and is suppressed linearly for P > 6.5 GPa with a gradual rate of dT c /dP ∼ -0.05 K/GPa [278]. In contrast, the superconducting state of UNi 2 Al 3 is suppressed at a relatively rapid rate of dT c /dP ∼ -0.24(3) K/GPa under low applied pressures [279].…”

Section: Introductionmentioning

confidence: 96%

Unconventional superconductivity in heavy-fermion compounds

White

Thompson

Maple

2015

Physica C: Superconductivity and its Applications

126

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Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion compounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. We conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.

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The heavy-fermion superconductor UPd₂Al₃at very high pressure

Cited by 13 publications

References 9 publications

Magnetically driven superconductivity in CeCu2Si2

Magnetically driven superconductivity in CeCu2Si2

Superconducting phases off-electron compounds

Unconventional superconductivity in heavy-fermion compounds

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The heavy-fermion superconductor UPd2Al3at very high pressure

Cited by 13 publications

References 9 publications

Magnetically driven superconductivity in CeCu2Si2

Magnetically driven superconductivity in CeCu2Si2

Superconducting phases off-electron compounds

Unconventional superconductivity in heavy-fermion compounds

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The heavy-fermion superconductor UPd₂Al₃at very high pressure