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Register a new userEvidence for a Novel State of Superconductivity in Noncentrosymmetric CePt3Si : A 195Pt-NMR Study
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We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt3Si through measurements of the 195Pt nuclear spin-lattice relaxation rate 1/T_1. In the normal state, the temperature (T) dependence of 1/T1 unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy fermion (HF) state. The coexistence of AFM and SC phases, that emerge at TN = 2.2 K and Tc = 0.75 K, respectively, takes place on a microscopic level. CePt3Si is the first HF superconductor that reveals a peak in 1/T1 just below Tc and, additionally, does not follow the T^3 law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristics may be related with the lack of an inversion center in its crystal structure.
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We report the measurements of the $^{29}$Si Knight shift $^{29}K$ on the noncentrosymmetric heavy-fermion compound CePt$_{3}$Si in which antiferromagnetism (AFM) with $T_{rm N}=2.2$ K coexists with superconductivity (SC) with $T_{c}=0.75$ K. Its spin part $^{29}K_{rm s}$, which is deduced to be $K_{rm s}^{c}ge 0.11$ and 0.16% at respective magnetic fields $H=2.0061$ and 0.8671 T, does not decrease across the superconducting transition temperature $T_{c}$ for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of $^{195}$Pt below $T_{c}$ has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt$_{3}$Si.
In this article, we report the temperature dependence of spin-lattice relaxation rates at two Pt sites and one Si site in CePt3Si with a non-centrosymmetric structure center. 1/T1 for both Pt sites between 2 K and 300 K and 1/T1 of Si above 3 K might be explained by the contributions from the low-lying crystal-electric-field level and the quasiparticle due to the hybridization between the ground state and conduction electrons. Just below Tc no remarkable enhancement in 1/T1 was observed. The estimated value of superconducting gap is about 2Delta = 3kBTc.
We report the magnetic and superconducting properties of locally noncentrosymmetric SrPtAs obtained by muon-spin-rotation/relaxation (muSR) measurements. Zero-field muSR reveals the occurrence of small spontaneous static magnetic fields with the onset of superconductivity. This finding suggests that the superconducting state of SrPtAs breaks time-reversal symmetry. The superfluid density as determined by transverse field muSR is nearly flat approaching T = 0 K proving the absence of extended nodes in the gap function. By symmetry, several superconducting states supporting time-reversal symmetry breaking in SrPtAs are allowed. Out of these, a dominantly d + id (chiral d-wave) order parameter is most consistent with our experimental data.
Comprehensive low-temperature specific heat data C(T,H) of Na_0.35CoO2-1.3H_2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. For the normal state, the values of gamma_n=13.94 mJ/mol K2, and Debye temperature 362 K are reported. At zero field, a very sharp superconducting anomaly was observed at Tc=4.5 K with DeltaC/gamma_nTc=1.45. The superconducting volume fraction is estimated to be 47.4 % based on the consideration of entropy balance at Tc for the second-order superconducting phase transition. In the superconducting state, the electronic contribution C_es at H=0 can be well described by the model of the line nodal order parameter. In low H, gamma(H) H^1/2 which is also a manifestation of the line nodes. The behaviors of both Tc(H) and gamma(H) suggest the anisotropy of Hc2 or possible crossovers or transitions occurring in the mixed state.
The noncentrosymmetric superconductor Mo$_3$Rh$_2$N, with $T_c = 4.6$ K, adopts a $beta$-Mn-type structure (space group $P$4$_1$32), similar to that of Mo$_3$Al$_2$C. Its bulk superconductivity was characterized by magnetization and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($mu$SR). The low-temperature superfluid density, measured via transverse-field (TF)-$mu$SR, evidences a fully-gapped superconducting state with $Delta_0 = 1.73 k_mathrm{B}T_c$, very close to 1.76 $k_mathrm{B}T_c$ - the BCS gap value for the weak coupling case, and a magnetic penetration depth $lambda_0 = 586$ nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined by zero-field (ZF)-$mu$SR measurements, hints at a preserved time-reversal symmetry in the superconducting state. Both TF-and ZF-$mu$SR results evidence a spin-singlet pairing in Mo$_3$Rh$_2$N.
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