High-Pressure Study of the Ground- and Superconducting-State Properties of CeAu2Si2 (original) (raw)
Related papers
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.
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.
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.
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.
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
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.
Philosophical Magazine, 2018
In this paper the low-temperature properties of two isostructural canonical heavy-fermion compounds are contrasted with regards to the interplay between antiferromagnetic (AF) quantum criticality and superconductivity. For CeCu 2 Si 2 , fully-gapped d-wave superconductivity forms in the vicinity of an itinerant three-dimensional heavy-fermion spin-density-wave (SDW) quantum critical point (QCP). Inelastic neutron scattering results highlight that both quantum critical SDW fluctuations as well as Mott-type fluctuations of local magnetic moments contribute to the formation of Cooper pairs in CeCu 2 Si 2. In YbRh 2 Si 2 , superconductivity appears to be suppressed at T ≳ 10 mK by AF order (T N = 70 mK). Ultra-low temperature measurements reveal a hybrid order between nuclear and 4f-electronic spins, which is dominated by the Yb-derived nuclear spins, to develop at T A slightly above 2 mK. The hybrid order turns out to strongly compete with the primary 4felectronic order and to push the material towards its QCP. Apparently, this paves the way for heavy-fermion superconductivity to form at T c = 2 mK. Like the pressure-induced QCP in CeRhIn 5 , the magnetic field-induced one in YbRh 2 Si 2 is of the local Kondo-destroying variety which corresponds to a Mott-type transition at zero temperature. Therefore, these materials form the link between the large family of about fifty low-T unconventional heavyfermion superconductors and other families of unconventional superconductors with higher T c s, notably the doped Mott insulators of the cuprates, organic charge-transfer salts and some of the Fe-based superconductors. Our study suggests that heavy-fermion superconductivity near an AF QCP is a robust phenomenon. Heavy-fermion metals, superconductivity, quantum critical phenomena 1. Quantum criticality in antiferromagnetic heavy-fermion metals Unconventional superconductivity, i.e., superconductivity which is not driven by lattice vibrations, frequently develops in strongly correlated metals on the brink of antiferromagnetic (AF) order [1, 2]. The continuous suppression of AF order by non-thermal control parameters, such as external/chemical pressure and magnetic field gives rise to a quantum critical point (QCP) which determines the physical properties in a wide range of parameters. Strong deviations from the predictions of Landau's Fermi-liquid theory [3], socalled non-Fermi-liquid (NFL) phenomena, are commonly observed in the normal metallic state out of which superconductivity develops. The interplay between quantum criticality and superconductivity in strongly correlated electron systems is a timely, controversial and much debated topic which has been studied over the last two decades, most intensively with AF heavy-fermion metals [4, 5]. These are intermetallic compounds of certain lanthanides, such as Ce and Yb, or actinides, such as U and Pu. The lanthanide-based heavyfermion metals are model systems for the Kondo lattice, where at the QCP the on-site Kondo screening, characterized by k B T K , with T K being the Kondo temperature of the crystalfield (CF)-derived lowest-lying Kramers doublet of the localized 4f-shell, exactly cancels the intersite magnetic Ruderman Kittel Kasuya Yoshida (RKKY) interaction, characterized by k B T RKKY. So far, two different types of AF QCPs have been established for heavy-fermion metals. Some of them exhibit a "conventional" QCP, which means that in this scenario the AF order is of itinerant nature [6-8]. This kind of spin-density wave (SDW) order, with three-dimensional (3D) quantum critical fluctuations of the AF order parameter, is common to transition-metal compounds where d-electrons contribute to the conduction band. A 2. CeCu 2 Si 2 : Fully gapped d-wave superconductivity in the vicinity of a threedimensional spin-density-wave quantum critical point Heavy-fermion superconductivity was first discovered in the Kondo lattice system CeCu 2 Si 2 with almost trivalent Ce (T K ≃ 20 K) [21]. It has been considered an unconventional superconductor from early on: (i) The non-f-electron reference compound LaCu 2 Si 2 does not superconduct (at T ≥ 20 mK) [21], which implies that superconductivity in the Ce homologue should be ascribed to the periodic lattice of 100 % magnetic Ce 3+ ions. (ii) The reduced jump in the Sommerfeld coefficient of the electronic specific heat [γ(T) = C(T)/T] at the superconducting transition temperature, ΔC/γ 0 T c [γ 0 ≃1 J/(K 2 mol)], is of order unity, which implies that the Cooper pairs are formed by heavy-mass quasiparticles, i.e., slowly propagating Kondo singlets. As their Fermi velocity v F * is only of the order of the velocity of sound, the electron-phonon interaction is not retarded, i.e., the direct Coulomb repulsion among the charge carriers cannot be avoided. (iii) Therefore, an alternative pairing mechanism must be at work which, in analogy to superfluidity in 3 He [22], was early on assumed to be magnetic in origin [23-25]. (iv) Already a tiny amount of nonmagnetic impurities was found to fully suppress superconductivity in CeCu 2 Si 2 [26], similar to the
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%.