Pressure-induced change of the pairing symmetry in superconducting CeCu2Si2 (original) (raw)
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Pressure Tuning of the Interplay of Magnetism and Superconductivity in CeCu2Si2
2011
We carried out specific-heat and ac-susceptibility experiments under hydrostatic pressure to investigate the interplay of spin-density-wave antiferromagnetism (A) and superconductivity (S) in single-crystalline AS-type CeCu2Si2. We find evidence for a line of magnetic-field-and pressuretuned quantum critical points in the normal state in the zero-temperature magnetic field-pressure plane. Our analysis suggests an extension of this line into the superconducting state and corroborates the close connection of the underlying mechanisms leading to the formation of the antiferromagnetic and the superconducting states in AS-type CeCu2Si2.
High-Pressure Study of the Ground- and Superconducting-State Properties of CeAu2Si2
Journal of the Physical Society of Japan, 2017
The pressure-temperature phase diagram of the new heavy-fermion superconductor CeAu2Si2 is markedly different from those studied previously. Indeed, superconductivity emerges not on the verge but deep inside the magnetic phase, and mysteriously Tc increases with the strengthening of magnetism. In this context, we have carried out ac calorimetry, resistivity, and thermoelectric power measurements on a CeAu2Si2 single crystal under high pressure. We uncover a strong link between the enhancement of superconductivity and quantum-critical-like features in the normal-state resistivity. Non-Fermi-liquid behavior is observed around the maximum of superconductivity and enhanced scattering rates are observed close to both the emergence and the maximum of superconductivity. Furthermore we observe signatures of pressure-and temperature-driven modifications of the magnetic structure inside the antiferromagnetic phase. A comparison of the features of CeAu2Si2 and its parent compounds CeCu2Si2 and CeCu2Ge2 plotted as function of the unit-cell volume leads us to propose that critical fluctuations of a valence crossover play a crucial role in the superconducting pairing mechanism. Our study illustrates the complex interplay between magnetism, valence fluctuations, and superconductivity.
Solid State Communications, 2015
Taking advantage of a novel multiprobe setup we have measured, on a unique sample, the acmagnetic susceptibility, the resistivity, the ac-specific heat and the thermopower of the superconductor heavy fermion CeCu2Si2 under pressure up to 5.1 GPa. At the superconducting transition temperature Tc, the Meissner signal corresponds to that expected for the sample volume and coincides with the specific heat jump and the resistive transition completion temperatures. Differing from previous observations, here the susceptibility measurements did not reveal any anomaly in the vicinity of the resistive transition onset.
Competition between magnetism and superconductivity in CeCu2Si2
Physical Review B, 1997
The interplay between superconductivity and magnetism in CeCu2Si2 has been investigated by means of microprobe, muon spin rotation and relaxation (muSR), and specific-heat measurements on four slightly off-stoichiometric polycrystalline samples Ce1+xCu2+ySi2. Microprobe analysis reveals that within the errors (+/-3%) the main phases of all four samples exhibit the ideal stoichiometry 1:2:2 and their relative composition varies by less than 2%.
Effect of disorder on the pressure-induced superconducting state of CeAu 2 Si 2
Physical Review B, 2015
CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor which shows very unusual interplay between superconductivity and magnetism under pressure. Here we compare the results of high-pressure measurements on single crystalline CeAu2Si2 samples with different levels of disorder. It is found that while the magnetic properties are essentially sample independent, superconductivity is rapidly suppressed when the residual resistivity of the sample increases. We show that the depression of bulk Tc can be well understood in terms of pair breaking by nonmagnetic disorder, which strongly suggests an unconventional pairing state in pressurized CeAu2Si2. Furthermore, increasing the level of disorder leads to the emergence of another phase transition at T * within the magnetic phase, which might be in competition with superconductivity.
On the competition between superconductivity and magnetism in CeCu2Si2
Physica B: Condensed Matter, 1995
Muon spin relaxation measurements in zero magnetic field on several polycrystalline samples provide evidence that superconductivity and magnetic order do not coexist on a microscopic scale but develop inhomogeneously in Cel+xCu2+rSi2. The distribution of magnetic and superconducting domains depends on the temperature and sensitively on variations of the stoichiometry. Superconductivity sets in first in the paramagnetic domains and, on further cooling, reduces the magnetically ordered volume fraction. However, in all samples down to T = 60 mK considerable portions remain magnetic.
Competition between Magnetic Order and Superconductivity in CeCu2.2Si2
Physical Review Letters, 1994
We describe muon spin relaxation measurements of the magnetic heavy fermion compound CeCu22Si2. Static magnetic order appears below about 1 K, most likely of spin glass nature. We find that the superconducting transition onsetting at 0.6 K partially destroys the magnetic state and that the magnetic volume fraction decreases within the superconducting state. This observation supports the idea that in CeCu22Si2, magnetic order and superconductivity compete with each other rather than coexist.
Is CeCu2 a pressure-induced heavy-fermion superconductor?
Physica B: Condensed Matter, 1997
The electrical resistivity of both polycrystalline and single crystal CeCu2 has been studied under pressure up to 8.3 GPa for temperatures down to 24mK. With increasing pressure, the Kondo effect develops while the magnetic ordering temperature rises, in agreement with the diagram of Doniach. Near a critical pressure Pc ~6GPa, which seems to coincide with a structural change, the magnetic ordering vanishes and the electrical resistivity p(T) recovers a Fermi liquid behaviour with p oc AT 2. The coefficient A indicates that the electronic effective masses are much heavier than at zero pressure. In a narrow pressure window around Pc, i.e. near the magnetic instability of CeCu2, the electrical resistivity measurements show an onset of superconductivity at 0.15-0.18 K. The very high initial slope, B~2 ~ -5T/K of the upper critical field strongly suggests heavy fermion superconductivity.
Colloquium : Unconventional fully gapped superconductivity in the heavy-fermion metal CeCu2Si2
Reviews of Modern Physics
The heavy-fermion metal CeCu 2 Si 2 was the first discovered unconventional, non-phonon-mediated superconductor and, for a long time, was believed to exhibit single-band d-wave superconductivity, as inferred from various measurements hinting at a nodal gap structure. More recently, however, measurements using a range of techniques at low temperatures (T âȘ 0.1 K) provided evidence for a fully gapped superconducting order parameter. In this Colloquium, after a historical overview the apparently conflicting results of numerous experimental studies on this compound are surveyed. The different theoretical scenarios that have been applied to understanding the particular gap structure are then addressed, including both isotropic (sign-preserving) and anisotropic two-band s-wave superconductivity, as well as an effective two-band d-wave model, where the latter can explain the currently available experimental data on CeCu 2 Si 2. The lessons from CeCu 2 Si 2 are expected to help uncover the Cooper-pair states in other unconventional, fully gapped superconductors with strongly correlated carriers, and, in particular, highlight the rich variety of such states enabled by orbital degrees of freedom.