243 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

    Anomalous quasiparticle transport in the superconducting state of CeCoIn5

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    We report on a study of thermal Hall conductivity k_xy in the superconducting state of CeCoIn_5. The scaling relation and the density of states of the delocalized quasiparticles, both obtained from k_xy, are consistent with d-wave superconducting symmetry. The onset of superconductivity is accompanied by a steep increase in the thermal Hall angle, pointing to a striking enhancement in the quasiparticle mean free path. This enhancement is drastically suppressed in a very weak magnetic field. These results highlight that CeCoIn_5 is unique among superconductors. A small Fermi energy, a large superconducting gap, a short coherence length, and a long mean free path all indicate that CeCoIn_5 is clearly in the superclean regime (E_F/Delta<<l/xi), in which peculiar vortex state is expected.Comment: 5 pages, 5 figure

    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

    Thermoelectric response near a quantum critical point: the case of CeCoIn5

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    We present a study of thermoelectric coefficients in CeCoIn_5 down to 0.1 K and up to 16 T in order to probe the thermoelectric signatures of quantum criticality. In the vicinity of the field-induced quantum critical point, the Nernst coefficient nu exhibits a dramatic enhancement without saturation down to lowest measured temperature. The dimensionless ratio of Seebeck coefficient to electronic specific heat shows a minimum at a temperature close to threshold of the quasiparticle formation. Close to T_c(H), in the vortex-liquid state, the Nernst coefficient behaves anomalously in puzzling contrast with other superconductors and standard vortex dynamics.Comment: 4 pages, 4 figures,final published versio

    ^{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.

    Ordered magnetic and quadrupolar states under hydrostatic pressure in orthorhombic PrCu2

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    We report magnetic susceptibility and electrical resistivity measurements on single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which pressure range covers the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that in the pressure-induced magnetic state the ordered 4f-moments lie in the ac-plane. We propose that remarkable pressure effects on the susceptibility and resistivity are due to changes in the quadrupolar state of O22 and/or O20 under pressure. We present a simple analysis in terms of the singlet-singlet model.Comment: 14 pages, 9 figures submitted to Phys. Rev.
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