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Register a new userEffect of Zn substitution for Cu on Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$ near the hole concentration of 1/8 per Cu
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A weakening of superconductivity upon substitution of Cu by Zn (0.5~1 %) is observed in a high-T_c cuprate, Ca_{2-x}Na_xCuO2Cl2, near the hole concentration of 1/8 per Cu. The superconducting transition temperature and its volume fraction, estimated by magnetic susceptibility, exhibit a sizable anomaly for x=0.12~0.14, where the slowing down of Cu spin fluctuations below 5 K is demonstrated by muon spin relaxation experiments. These observations are in close resemblance to other typical cuprates including YBa2Cu3O_{7-d}, and Bi2Sr2Ca_{1-x}Y_xCu2O_{8+d}, providing further evidence that Zn-induced stripe correlation is a universal feature of high-T_c cuprate superconductors common to that of La_{2-x}A_{x}CuO4 (A=Ba, Sr).
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In conventional superconductors, magnetic impurities form an impurity band due to quantum interference of the impurity bound states, leading to suppression of the superconducting transition temperature. Such quantum interference effects can also be expected in d-wave superconductors. Here, we use scanning tunneling microscopy to investigate the effect of multiple non-magnetic impurities on the local electronic structure of the high-temperature superconductor Bi$_{2}$Sr$_{2}$Ca(Cu$_{1-x}$Zn$_{x}$)$_{2}$O$_{8+delta}$. We find several fingerprints of quantum interference of the impurity bound states including: (i) a two-dimensional modulation of local density-of-states with a period of approximately 5.4 AA along the $a$- and $b$-axes, which is indicative of the d-wave superconducting nature of the cuprates; (ii) abrupt spatial variations of the impurity bound state energy; (iii)an appearance of positive energy states; (iv) a split of the impurity bound state. All of these findings provide important insight into how the impurity band in d-wave superconductors is formed.
We estimated the ratios of $^{63}$Cu hyperfine coupling constants in the double-layer high-$T_mathrm{c}$ superconductor HgBa$_2$CaCu$_2$O$_{6+delta}$ from the anisotropies in Cu nuclear spin-lattice relaxation rates and spin Knight shifts to study the nature of the ultraslow fluctuations causing the $T_2$ anomaly in the Cu nuclear spin-echo decay. The ultraslow fluctuations may come from uniform magnetic fluctuations spread around the wave vector $q$ = 0, otherwise the electric origins.
We report experimental evidence for the spatial variation of hole concentration x_(hole) in the high Tc superconductor La(2-x)Sr(x)CuO(4) (0.04 <= x <= 0.16) by using (63)Cu NQR for (63)Cu isotope enriched samples. We demonstrate that the extent of the spatial variation of the local hole concentration D(x)_(hole) is reflected on (63)1/T1 and deduce the temperature dependence. D(x)_(hole) increases below 500 - 600K, and reaches values as large as D(x)_(hole)/x ~ 0.5 below ~ 150K. We estimate the length scale of the spatial variation in x_(hole) to be R_(hole) >~ 3nm from analysis of the NQR spectrum.
The internal magnetic field distribution in a mixed state of a cuprate superconductor, Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ ($T_{rm c}simeq28.5$ K, near the optimal doping), was measured by muon spin rotation ($mu$SR) technique up to 60 kOe. The $mu$SR linewidth $Lambda(B)$ which exhibits excess broadening at higher fields ($B>5$ kOe) due to field-induced magnetism (FIM), is described by a relation, $Lambda(B)proptosqrt{B}$. This suggests that the orbital current and associated quasiparticle excitation plays predominant roles in stabilizing the quasistatic correlation. Moreover, a slowing down of the vortex fluctuation sets in well above $T_{rm c}$, as inferred from the trace of FIM observed up to $sim80$ K, and develops continuously without a singularity at $T_{rm c}$ as the temperature decreases.
Pulsed NQR at the frequencies of 28-33 MHz has been used to study copper NQR spectra in YBa{2}Cu{3}O{7}, TmBa{2}Cu{3}O{7} and Y{0.9}Pr{0.1}Ba{2}Cu{3}O{7} compounds at temperatures of 4.2-200K. Quantitative analysis of the spectra has shown that the plane Cu(2) spectra shape is well described by using a model of 1D correlations of charge and spin distribution in CuO{2} planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO{2} planes, but doping the YBa{2}Cu{3}O{7} lattice with praseodymium slows this motion down.
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