14 research outputs found
Spin singlet pairing in the superconducting state of NaxCoO2\cdot1.3H2O: evidence from a ^{59}Co Knight shift in a single crystal
We report a ^{59}Co Knight shift measurement in a single crystal of the
cobalt oxide superconductor Na_{x}CoO_2\cdot1.3H_2O (T_c=4.25 K). We find that
the shift due to the spin susceptibility, K^s, is substantially large and
anisotropic, with the spin shift along the a-axis K^s_a being two times that
along the c-axis K^s_c. The shift decreases with decreasing temperature (T)
down to T\sim100 K, then becomes a constant until superconductivity sets in.
Both K^s_a and K^s_c decrease below T_c. Our results indicate unambiguously
that the electron pairing in the superconducting state is in the spin singlet
form.Comment: 4 pages, 5 figure
Single crystal growth of and hyperfine couplings in the spin-triplet superconductor KCrAs
We report single crystal growth of strongly-correlated compound
KCrAs with superconducting temperature =6.2 K, and
the measurements of magnetic susceptibility above . We
determined the hyperfine coupling constants directly from the relation between
the Knight shift () and susceptibility (- plot) and obtained the
orbital contribution . Our results of is
in fairly good agreement with the previous estimate using a novel method, and
reinforce the conclusion that KCrAs is a spin-triplet
superconductor
Na content dependence of superconductivity and the spin correlations in Na_{x}CoO_{2}\cdot 1.3H_{2}O
We report systematic measurements using the ^{59}Co nuclear quadrupole
resonance(NQR) technique on the cobalt oxide superconductors Na_{x}CoO_{2}\cdot
1.3H_{2}O over a wide Na content range x=0.25\sim 0.34. We find that T_c
increases with decreasing x but reaches to a plateau for x \leq0.28. In the
sample with x \sim 0.26, the spin-lattice relaxation rate 1/T_1 shows a T^3
variation below T_c and down to T\sim T_c/6, which unambiguously indicates the
presence of line nodes in the superconducting (SC) gap function. However, for
larger or smaller x, 1/T_1 deviates from the T^3 variation below T\sim 2 K even
though the T_c (\sim 4.7 K) is similar, which suggests an unusual evolution of
the SC state. In the normal state, the spin correlations at a finite wave
vector become stronger upon decreasing x, and the density of states at the
Fermi level increases with decreasing x, which can be understood in terms of a
single-orbital picture suggested on the basis of LDA calculation.Comment: version published in J. Phys. Condens. Matter (references updated and
more added
Spin-singlet superconductivity in the doped topological crystalline insulator Sn0.96In0.04Te
The In-doped topological crystalline insulator Sn1−x InxTe is a candidate for a topological superconductor, where a pseudo-spin-triplet state has been proposed. To clarify the spin symmetry of Sn1−x InxTe, we perform 125Te-nuclear magnetic resonance (NMR) measurements in polycrystalline samples with 0 x 0.15. The penetration depth calculated from the NMR line width is T independent below half the superconducting transition temperature (Tc) in polycrystalline Sn0.96In0.04Te, which indicates a fully opened superconducting gap. In this sample, the spin susceptibility measured by the spin Knight shift (Ks) at an external magnetic field of μ0H0 = 0.0872 T decreases below Tc, and Ks(T = 0)/Ks(T = Tc) reaches 0.36 ± 0.10, which is far below the limiting value 2/3 expected for a spin-triplet state for a cubic crystal structure. Our result indicates that polycrystalline Sn0.96In0.04Te is a spin-singlet superconductor
Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5
A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure T-c. (P)-dependent In-115 nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh0.5Ir0.5In5. These experiments reveal an antiferromagnetic (AF) QCP at P-c(AF) = 1.2 GPa where a dome of superconductivity reaches a maximum transition temperature Tc. Preceding P-c(AF), however, the NQR frequency nu(Q) undergoes an abrupt increase at P-c* = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's f-electron and associated small-to-large change in the Fermi surface. At P-c(AF) where T-c is optimized, there is an unusually large fraction of gapless excitations well below T-c that implicates spin-singlet, odd-frequency pairing symmetry
Spin singlet pairing in the superconducting state of NaxCo02 1.3H2O: evidence from a 59Co Knight shift in a single crystal
We report a 59Co Knight-shift measurement in a single crystal of the cobalt oxide superconductor NaxCoO2∙1.3H2O (Tc=4.25 K). We find that the shift due to the spin susceptibility, Ks, is substantially large and anisotropic, with the spin shift along the a-axis Kas being two times that along the c-axis Kcs. The shift decreases with decreasing temperature (T) down to T≈100 K, then becomes a constant until superconductivity sets in. Both Kas and Kcs decrease below Tc. Our results indicate unambiguously that the electron pairing in the superconducting state is in the spin singlet form