225 research outputs found
Electronic structure and electric-field gradients analysis in
Electric field gradients (EFG's) were calculated for the compound at
both and sites. The calculations were performed within
the density functional theory (DFT) using the augmented plane waves plus local
orbital (APW+lo) method employing the so-called LDA+U scheme. The
compound were treated as nonmagnetic, ferromagnetic, and antiferromagnetic
cases. Our result shows that the calculated EFG's are dominated at the
site by the Ce-4f states. An approximately linear relation is
intuited between the main component of the EFG's and total density of states
(DOS) at Fermi level. The EFG's from our LDA+U calculations are in better
agreement with experiment than previous EFG results, where appropriate
correlations had not been taken into account among 4f-electrons. Our result
indicates that correlations among 4f-electrons play an important role in this
compound and must be taken into account
Density of States and NMR Relaxation Rate in Anisotropic Superconductivity with Intersecting Line Nodes
We show that the density of states in an anisotropic superconductor with
intersecting line nodes in the gap function is proportional to for , where is the maximum value of
the gap function and is constant, while it is proportional to if
the line nodes do not intersect. As a result, a logarithmic correction appears
in the temperature dependence of the NMR relaxation rate and the specific heat,
which can be observed experimentally. By comparing with those for the heavy
fermion superconductors, we can obtain information about the symmetry of the
gap function.Comment: 7 pages, 4 PostScript Figures, LaTeX, to appear in J. Phys. Soc. Jp
Unconventional Superconductivity in Heavy Fermion Systems
We review the studies on the emergent phases of superconductvity and
magnetism in the -electron derived heavy-fermion (HF) systems by means of
the nuclear-quadrupole-resonance (NQR) under pressure. These studies have
unraveled a rich variety of the phenomena in the ground state of HF systems. In
this article, we highlight the novel phase diagrams of magnetism and
unconventional superconductivity (SC) in CeCuSi, HF antiferromagnets
CeRhIn, and CeIn. A new light is shed on the difference and common
features on the interplay between magnetism and SC on the magnetic criticality.Comment: 15 pages, 13 figures, to appear in J. Phys. Soc. JPN, 74, No.1
(2005), special issue "Kondo Effect- 40 Years after the Discovery
Pressure-induced unconventional superconductivity in the heavy-fermion antiferromagnet CeIn3: An 115In-NQR study under pressure
We report on the pressure-induced unconventional superconductivity in the
heavy-fermion antiferromagnet CeIn3 by means of nuclear-quadrupole-resonance
(NQR) studies conducted under a high pressure. The temperature and pressure
dependences of the NQR spectra have revealed a first-order quantum-phase
transition (QPT) from an AFM to PM at a critical pressure Pc=2.46 GPa. Despite
the lack of an AFM quantum critical point in the P-T phase diagram, we
highlight the fact that the unconventional SC occurs in both phases of the AFM
and PM. The nuclear spin-lattice relaxation rate 1/T1 in the AFM phase have
provided evidence for the uniformly coexisting AFM+SC phase. In the HF-PM phase
where AFM fluctuations are not developed, 1/T1 decreases without the coherence
peak just below Tc, followed by a power-law like T dependence that indicates an
unconventional SC with a line-node gap. Remarkably, Tc has a peak around Pc in
the HF-PM phase as well as in the AFM phase. In other words, an SC dome exists
with a maximum value of Tc = 230 mK around Pc, indicating that the origin of
the pressure-induced HF SC in CeIn3 is not relevant to AFM spin fluctuations
but to the emergence of the first-order QPT in CeIn3. When the AFM critical
temperature is suppressed at the termination point of the first-order QPT, Pc =
2.46 GPa, the diverging AFM spin-density fluctuations emerge at the critical
point from the AFM to PM. The results with CeIn3 leading to a new type of
quantum criticality deserve further theoretical investigations
Enhancing the Superconducting Transition Temperature due to Strong-Coupling Effect under Antiferromagnetic Spin Fluctuations in CeRh1-xIrxIn5 : 115In-NQR Study
We report on systematic evolutions of antiferromagnetic (AFM) spin
fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF)
compounds CeRhIrIn via In
nuclear-quadrupole-resonance (NQR) experiment. The measurements of nuclear
spin-lattice relaxation rate have revealed the marked development of
AFM spin fluctuations as a consequence of approaching an AFM ordered state with
increasing Rh content. Concomitantly the superconducting transition temperature
and the energy gap increase drastically from K and in CeIrIn up to K and in
CeRhIrIn, respectively. The present work suggests that the
AFM spin fluctuations in close proximity to the AFM quantum critical point are
indeed responsible for the onset of strong-coupling unconventional SC with the
line node in the gap function in HF compounds.Comment: 4pages,5figures,to appear in Phys. Rev. Let
New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn
We report the discovery of new superconducting and novel magnetic phases in
CeIn on the verge of antiferromagnetism (AFM) under pressure () through
the In-nuclear quadrupole resonance (NQR) measurements. We have found a
-induced phase separation of AFM and paramagnetism (PM) without any trace
for a quantum phase transition in CeIn. A new type of superconductivity
(SC) was found in GPa to coexist with AFM that is magnetically
separated from PM where the heavy fermion SC takes place. We propose that the
magnetic excitations such as spin-density fluctuations induced by the
first-order magnetic phase transition might mediate attractive interaction to
form Cooper pairs.Comment: 4 pages, 4 EPS figures, submitted to J. Phys. Soc. Jp
Gapless Magnetic and Quasiparticle Excitations due to the Coexistence of Antiferromagnetism and Superconductivity in CeRhIn : A study of In-NQR under Pressure
We report systematic measurements of ac-susceptibility,
nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time
() on the pressure ()- induced heavy-fermion (HF) superconductor
CeRhIn. The temperature () dependence of at = 1.6 GPa has
revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist
microscopically, exhibiting the respective transition at K and
= 0.9 K. It is demonstrated that SC does not yield any trace of gap
opening in low-lying excitations below K, but K, followed by a = const law. These results point to the
unconventional characteristics of SC coexisting with AFM. We highlight that
both of the results deserve theoretical work on the gapless nature in low-lying
excitation spectrum due to the coexistence of AFM and SC and the lack of the
mean-field regime below K.Comment: 4pages,5figures,revised versio
Unique Spin Dynamics and Unconventional Superconductivity in the Layered Heavy Fermion Compound CeIrIn_5:NQR Evidence
We report measurements of the ^{115}In nuclear spin-lattice relaxation rate
(1/T_1) between T=0.09 K and 100 K in the new heavy fermion (HF) compound
CeIrIn_5. At 0.4 K < T < 100 K, 1/T_1 is strongly T-dependent, which indicates
that CeIrIn_5 is much more itinerant than known Ce-based HFs. We find that
1/T_1T, subtracting that for LaIrIn_5, follows a 1/(T+\theta)^{3/4} variation
with \theta=8 K. We argue that this novel feature points to anisotropic, due to
a layered crystal structure, spin fluctuations near a magnetic ordering. The
bulk superconductivity sets in at 0.40 K below which the coherence peak is
absent and 1/T_1 follows a T^3 variation, which suggests unconventional
superconductivity with line-node gap.Comment: minor changes, appeared in PRL (4 pages, 4 figures
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