Yu Kawasaki

Evidence for unconventional strong-coupling superconductivity in PrOs4Sb12: an Sb nuclear quadrupole resonance study.

We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in Pr(Os4Sb12 with T(c)=1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate, 1/T(1), and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 approximately 10 K, associated with Pr3+(4f(2))-derived ground state. In the SC state, 1/T(1) shows neither a coherence peak just below T(c) K nor a T3-like power-law behavior observed for anisotropic HF superconductors with the line-node gap. The isotropic energy gap with its size Delta/k(B)=4.8 K seems to open up across T(c) below T(*) approximately 2.3 K. It is surprising that Pr(Os4Sb12 looks like an isotropic HF superconductor-it may indeed argue for Cooper pairing via quadrupolar fluctuations.

Coexistence of Antiferromagnetism and Superconductivity near the Quantum Criticality of the Heavy-Fermion Compound CeRhIn5

We report a study on the interplay between antiferromagnetism (AFM) and superconductivity (SC) in a heavy-fermion compound CeRhIn5 under pressure P=1.75 GPa. The onset of the magnetic order is evidenced from a clear split of 115In nuclear quadrupole resonance spectrum due to the spontaneous internal field below the Néel temperature T(N)=2.5 K. Simultaneously, bulk SC below T(c)=2.0 K is demonstrated by the observation of the Meissner diamagnetism signal whose size is the same as in the exclusively superconducting phase. These results indicate that the AFM coexists homogeneously with the SC at a microscopic level.

Gapless magnetic and quasiparticle excitations due to the coexistence of antiferromagnetism and superconductivity in CeRhIn5: a study of 115In NQR under pressure.

We report systematic measurements of ac susceptibility, nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time (T1) on the pressure (P)-induced heavy-fermion superconductor CeRhIn5. The temperature (T) dependence of 1/T(1) at P=1.6 GPa has revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist microscopically, exhibiting the respective transition at T(N)=2.8 K and T(MF)(c)=0.9 K. It is demonstrated that SC does not yield any trace of gap opening in low-lying excitations below T(onset)(c)=2 K, but T(MF)(c)=0.9 K, followed by a T(1)T=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 the low-lying excitation spectrum due to the coexistence of AFM and SC and the lack of the mean-field regime below T(onset)(c)=2 K.

Anisotropic Spin Fluctuations in Heavy-Fermion Superconductor CeCoIn5: In-NQR and Co-NMR Studies

We report In-NQR and Co-NMR experiments of CeCoIn 5 that undergoes a superconducting transition with a record high T c = 2.3 K to date among heavy-fermion superconductors. At zero magnetic field, a...

New Superconducting and Magnetic Phases Emerge on the Magnetic Criticality in CeIn3

We report the discovery of new superconducting and novel magnetic phases in CeIn 3 on the verge of antiferromagnetism (AFM) under pressure ( P ) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a P -induced phase separation of AFM and paramagnetism (PM) without any trace of a quantum phase transition in CeIn 3 . A new type of superconductivity (SC) was found, under P =2.28–2.5 GPa, to coexist with AFM. It 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.

Unconventional superconductivity in heavy-fermion systems

We review the studies on the emergent phases of superconductvity and magnetism in the f -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 CeCu 2 Si 2 , HF antiferromagnets CeRhIn 5 , and CeIn 3 . A new light is shed on the difference and common features on the interplay between magnetism and SC on the magnetic criticality.

µSR Studies on Heavy Fermion Superconductors CeIrIn5 and CeCoIn5

We report that the muon spin relaxation rate under zero-external field in the heavy-fermion compound Ce Tr In 5 ( Tr =Ir, Co) is independent of temperature down to 20 mK, demonstrating the absence of magnetism due to long-range magnetic order and/or to the breakdown of time-reversal symmetry in the superconducting state. The magnetic penetration depth deduced by the muon spin relaxation rate under a transverse field is λ∼6700 A for CeIrIn 5 at 402 G and ∼5500 A for CeCoIn 5 at 3 kG.

Exotic superconductivity in the coexistent phase of antiferromagnetism and superconductivity in CeCu2(Si0.98Ge0.02) 2: A Cu-NQR study under hydrostatic pressure

We report a pressure ( P ) effect on CeCu 2 (Si 0.98 Ge 0.02 ) 2 where an antiferromagnetic (AFM) order at T N ∼0.75 K coexists with superconductivity below T c ∼0.4 K. At pressures exceeding P = 0.19 GPa, the AFM order is suppressed, which demonstrates that the sudden emergence of AFM order due to the Ge doping is ascribed to the intrinsic lattice expansion. The exotic superconductivity at P = 0 GPa is found to evolve into a typical heavy-fermion one with a line-node gap above P = 0.91 GPa. We highlight that the anomalous enhancement in nuclear spin–lattice relaxation rate 1/ T 1 that follows a T 1 T = const. behavior well below T c at P = 0 GPa is characterized by the persistence of low-lying magnetic excitations, which may be inherent to the coexistent state of antiferromagnetism and superconductivity.We report a pressure (

Quasiparticle Excitation in the Superconducting Pyrochlore Cd2Re2O7 Probed by Muon Spin Rotation

P

Coexistence of antiferromagnetism and superconductivity in heavy-fermion systems

) effect on CeCu