1,015 research outputs found

### Strong Coupling between Antiferromagnetic and Superconducting Order Parameters in CeRhIn$_5$ Studied by In-NQR Spectroscopy

We report on a novel pressure ($P$)-induced evolution of magnetism and
superconductivity (SC) in a helical magnet CeRhIn$_5$ with an incommensurate
wave vector $Q_i=({1/2},{1/2},0.297)$ through the $^{115}$In nuclear quadrupole
resonance (NQR) measurements under $P$. Systematic measurements of the
$^{115}$In-NQR spectrum reveal that the commensurate antiferromagnetism (AFM)
with $Q_c=({1/2},{1/2},{1/2})$ is realized above $P_m \sim$ 1.7 GPa. An
important finding is that the size of SC gap and $T_c$ increase as the
magnitude of the AFM moment decreases in the $P$ 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 CeRhIn$_5$ : A study of $^{115}$In-NQR under Pressure

We report systematic measurements of ac-susceptibility,
nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time
($T_1$) on the pressure ($P$)- induced heavy-fermion (HF) superconductor
CeRhIn$_5$. 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 $T_c^{onset} = 2$ K, but $T_c^{MF} =
0.9$ K, followed by a $T_1T$ = 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 $T_c^{onset} = 2$ K.Comment: 4pages,5figures,revised versio

### Novel phase diagram for antiferromagnetism and superconductivity in pressure-induced heavy-fermion superconductor Ce$_2$RhIn$_8$ probed by In-NQR

We present a novel phase diagram for the antiferromagnetism and
superconductivity in Ce$_2$RhIn$_8$ probed by In-NQR studies under pressure
($P$). The quasi-2D character of antiferromagnetic spin fluctuations in the
paramagnetic state at $P$ = 0 evolves into a 3D character because of the
suppression of antiferromagnetic order for $P > P_{\rm QCP}\sim$ 1.36 GPa (QCP:
antiferromagnetic quantum critical point). Nuclear-spin-lattice-relaxation rate
$1/T_1$ measurements revealed that the superconducting order occurs in the $P$
range 1.36 -- 1.84 GPa, with maximum $T_c\sim$ 0.9 K around $P_{\rm QCP}\sim$
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

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

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

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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