High pressure investigation of superconducting signatures in CeCu2Si2: Ac- magnetic susceptibility and heat capacity, resistivity and thermopower (original) (raw)

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.

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.

Pressure-induced change of the pairing symmetry in superconducting CeCu2Si2

Physical Review B, 2009

Low-temperature (T) heat-capacity measurements under hydrostatic pressure up to p ≈ 2.1 GPa have been performed on single-crystalline CeCu2Si2. A broad superconducting (SC) region exists in the T − p phase diagram. In the low-pressure region antiferromagnetic spin fluctuations and in the high-pressure region valence fluctuations had previously been proposed to mediate Cooper pairing. We could identify these two distinct SC regions. We found different thermodynamic properties of the SC phase in both regions, supporting the proposal that different mechanisms might be implied in the formation of superconductivity. We suggest that different SC order parameters are characterizing the two distinct SC regions.

Pressure dependence of superconductivity in CeRh2As2

Physical Review B

In the recently discovered heavy fermion superconductor CeRh 2 As 2 , a magnetic-field-induced phase transition has been observed inside the superconducting state, which is proposed to be a transition from an even-to an odd-parity superconducting state. The odd-parity superconducting state and its large upper critical field has been explained by local inversion symmetry breaking and consequent Rashba spin-orbit coupling. Here, we report the experimental tuning of the superconductivity in CeRh 2 As 2 via applied pressure. Superconductivity is continuously suppressed up to 2.5 GPa. The kink in the upper critical field, which has been used to indicated the even-to odd-parity transition, is also suppressed, indicating the odd-parity state is suppressed faster than the even-parity state. Above 2.5 GPa, there might be a second dome of superconductivity, which requires further investigation.

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%.

High pressure-induced anomalous behavior in the mixed-valent superconductor CeRu3Si2

Journal of Magnetism and Magnetic Materials, 1986

Electrical resistivity of CeRu ,Si 2 has been measured from 290 to 1.1 K under high pressure up to 150 kbar. The initial strong suppressions in the resistivity and its T2-dependence, and the enhancement of T, were abruptly replaced by a pressure insensitive state above = 30 kbar which is presumably tetravalent

Giant Overlap between the Magnetic and Superconducting Phases of CeAu 2 Si 2 under Pressure

Physical Review X, 2014

High pressure provide a powerful means for exploring unconventional superconductivity which appears mostly on the border of magnetism. Here we report the discovery of pressure-induced heavy fermion superconductivity up to 2.5 K in the antiferromanget CeAu2Si2 (TN ≈ 10 K). Remarkably, the magnetic and superconducting phases are found to overlap across an unprecedentedly wide pressure interval from 11.8 to 22.3 GPa. Moreover, both the bulk Tc and TM are strongly enhanced when increasing the pressure from 16.7 to 20.2 GPa. Tc reaches a maximum at a pressure slightly below pc ≈ 22.5 GPa, at which magnetic order disappears. Furthermore, the scaling behavior of the resistivity provides evidence for a continuous delocalization of the Ce 4f -electrons associated with a critical endpoint lying just above pc. We show that the maximum Tc of CeAu2Si2 actually occurs at almost the same unit-cell volume as that of CeCu2Si2 and CeCu2Ge2, and when the Kondo and crystal field splitting energies becomes comparable. Dynamical mean-filed theory calculations suggest that the peculiar behavior in pressurized CeAu2Si2 might be related to its Ce 4f -orbital occupancy. Our results not only provide a unique example of the interplay between superconductivity and magnetism, but also underline the role of orbital physics in understanding Ce-based heavy fermion systems.