May 16, 2004
We report the discovery of exotic superconductivity (SC) and novel magnetism in heavy-fermion (HF) compounds, CeCu$_2$Si$_2$, CeRhIn$_5$ and CeIn$_3$ through nuclear-quadrupole-resonance (NQR) measurements under pressure ($P$). The exotic SC in a homogeneous CeCu$_2$Si$_2$ revealed antiferromagnetic critical fluctuations at the border to antiferromagnetism (AFM) or marginal AFM. The uniform mixed phase of SC and AFM in CeCu$_2$(Si$_{1-x}$Ge$_x$)$_2$ emerges on a microscopic level, once a tiny amount of 1%Ge($x=0.01$) is substituted for Si to expand its lattice. The application of minute pressure ($P\sim 0.19$ GPa) suppresses the sudden emergence of the AFM caused by doping Ge. The persistence of the low-lying magnetic excitations at temperatures lower than $T_c$ and $T_N$ is ascribed due to the uniform mixed phase of SC and AFM. Likewise, the $P$-induced HF superconductor CeRhIn$_5$ coexists with AFM on a microscopic level in $P = 1.5$ - 1.9 GPa. The unconventional gapless nature of SC in the low-lying excitation spectrum emerges due to the uniform mixed phase of AFM and SC. By contrast, in CeIn$_3$, we propose that the magnetic excitations such as spin-density fluctuations induced by the first-order phase transition from the AFM to the paramagnetism (PM) might mediate attractive interaction to form the Cooper pairs in the novel phase of AFM.
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December 11, 2004
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 li...
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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 for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where ...
February 15, 2008
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 un...
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We report a study on the interplay between antiferromagnetism (AFM) and superconductivity (SC) in a heavy-fermion compound CeRhIn$_5$ under pressure $P=1.75$ GPa. The onset of the magnetic order is evidenced from a clear split of $^{115}$In-NQR spectrum due to the spontaneous internal field below the N\'eel 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 ...
March 7, 2003
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