1,017 research outputs found

    Strong Coupling between Antiferromagnetic and Superconducting Order Parameters in CeRhIn5_5 Studied by In-NQR Spectroscopy

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    We report on a novel pressure (PP)-induced evolution of magnetism and superconductivity (SC) in a helical magnet CeRhIn5_5 with an incommensurate wave vector Qi=(1/2,1/2,0.297)Q_i=({1/2},{1/2},0.297) through the 115^{115}In nuclear quadrupole resonance (NQR) measurements under PP. Systematic measurements of the 115^{115}In-NQR spectrum reveal that the commensurate antiferromagnetism (AFM) with Qc=(1/2,1/2,1/2)Q_c=({1/2},{1/2},{1/2}) is realized above Pm∼P_m \sim 1.7 GPa. An important finding is that the size of SC gap and TcT_c increase as the magnitude of the AFM moment decreases in the PP region, where SC uniformly coexists with the commensurate AFM. This result provides evidence of strong coupling between the commensurate AFM order parameter (OP) and SC OP.Comment: 5 pages, 5 figure

    Gapless Magnetic and Quasiparticle Excitations due to the Coexistence of Antiferromagnetism and Superconductivity in CeRhIn5_5 : A study of 115^{115}In-NQR under Pressure

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    We report systematic measurements of ac-susceptibility, nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time (T1T_1) on the pressure (PP)- induced heavy-fermion (HF) superconductor CeRhIn5_5. The temperature (TT) dependence of 1/T11/T_1 at PP = 1.6 GPa has revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist microscopically, exhibiting the respective transition at TN=2.8T_N = 2.8 K and TcMFT^{MF}_c = 0.9 K. It is demonstrated that SC does not yield any trace of gap opening in low-lying excitations below Tconset=2T_c^{onset} = 2 K, but TcMF=0.9T_c^{MF} = 0.9 K, followed by a T1TT_1T = 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 Tconset=2T_c^{onset} = 2 K.Comment: 4pages,5figures,revised versio

    Novel phase diagram for antiferromagnetism and superconductivity in pressure-induced heavy-fermion superconductor Ce2_2RhIn8_8 probed by In-NQR

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    We present a novel phase diagram for the antiferromagnetism and superconductivity in Ce2_2RhIn8_8 probed by In-NQR studies under pressure (PP). The quasi-2D character of antiferromagnetic spin fluctuations in the paramagnetic state at PP = 0 evolves into a 3D character because of the suppression of antiferromagnetic order for P>PQCP∼P > P_{\rm QCP}\sim 1.36 GPa (QCP: antiferromagnetic quantum critical point). Nuclear-spin-lattice-relaxation rate 1/T11/T_1 measurements revealed that the superconducting order occurs in the PP range 1.36 -- 1.84 GPa, with maximum Tc∼T_c\sim 0.9 K around PQCP∼P_{\rm QCP}\sim 1.36 GPa.Comment: 5 pages, 5 figures, submitted to PR

    Density of States and NMR Relaxation Rate in Anisotropic Superconductivity with Intersecting Line Nodes

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    We show that the density of states in an anisotropic superconductor with intersecting line nodes in the gap function is proportional to Elog(αΔ0/E)E log (\alpha \Delta_0 /E) for ∣E∣<<Δ0|E| << \Delta_0, where Δ0\Delta_0 is the maximum value of the gap function and α\alpha is constant, while it is proportional to EE 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

    ^{115}In-NQR evidence for unconventional superconductivity in CeIn_3 under pressure

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    We report evidence for unconventional superconductivity in CeIn_3 at a pressure P = 2.65 GPa above critical pressure (P_c ~ 2.5 GPa) revealed by the measurements of nuclear-spin-lattice-relaxation time (T_1) and ac-susceptibility (ac-chi). Both the measurements of T_1 and ac-chi have pointed to a superconducting transition at T_c = 95 mK, which is much lower than an onset temperature T_{onset} = 0.15 K at zero resistance. The temperature dependence of 1/T_1 shows no coherence peak just below T_c, indicative of an unconventional nature for the superconductivity induced in CeIn_3.Comment: 4 pages, 4 figures, to be published in Phys.Rev.

    Emergent Phases of Nodeless and Nodal Superconductivity Separated by Antiferromagnetic Order in Iron-based Superconductor (Ca4Al2O6)Fe2(As1-xPx)2: 75As- and 31P-NMR Studies

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    We report 31^{31}P- and 75^{75}As-NMR studies on (Ca4_4Al2_2O6_{6})Fe2_2(As1−x_{1-x}Px_x)2_2 with an isovalent substitution of P for As. We present the novel evolution of emergent phases that the nodeless superconductivity (SC) in 0≤x≤\le x \le0.4 and the nodal one around xx=1 are intimately separated by the onset of a commensurate stripe-type antiferromagnetic (AFM) order in 0.5≤x≤\le x \le 0.95, as an isovalent substitution of P for As decreases a pnictogen height hPnh_{Pn} measured from the Fe plane. It is demonstrated that the AFM order takes place under a condition of 1.32\AA≤hPn≤\le h_{Pn} \le1.42\AA, which is also the case for other Fe-pnictides with the Fe2+^{2+} state in (FePnPn)−^{-} layers. This novel phase evolution with the variation in hPnh_{Pn} points to the importance of electron correlation for the emergence of SC as well as AFM order.Comment: 5pages, 4figures; accepted for publication as a Rapid Communication in Phys. Rev.
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