1,015 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.

    Universal behavior at discontinuous quantum phase transitions

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    Discontinuous quantum phase transitions besides their general interest are clearly relevant to the study of heavy fermions and magnetic transition metal compounds. Recent results show that in many systems belonging to these classes of materials, the magnetic transition changes from second order to first order as they approach the quantum critical point (QCP). We investigate here some mechanisms that may be responsible for this change. Specifically the coupling of the order parameter to soft modes and the competition between different types of order near the QCP. For weak first order quantum phase transitions general results are obtained. In particular we describe the thermodynamic behavior at this transition when it is approached from finite temperatures. This is the discontinuous equivalent of the non-Fermi liquid trajectory close to a conventional QCP in a heavy fermion material.Comment: 7 pages, 3 figure
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