Temperature Dependence of the Cu(2) NQR Line Width in YBa2_2Cu3_3O7−y_{7-y}

Systematic measurements of the $^{63}$Cu(2) NQR line width were performed in underdoped YBa$_2$Cu$_3$O$_{7-y}$ samples over the temperature range 4.2 K $<T<300$ K. It was shown that the copper NQR line width monotonically increases upon lowering temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed dependence is explained by the fact that the energy of a condensate of sliding charge-current states of the charge-density-wave type depends on the phase of order parameter. Calculations show that this dependence appears only at $T<T_c$. Quantitative estimates of the line broadening at $T<T_c$ agree with the measurement results.Comment: 4 pages, 2 figure

Temperature dependence of the Cu(2) NQR line width in YBa2Cu3O7 - y

Systematic measurements of the 63Cu(2) NQR line width were performed in underdoped YBa2Cu3O7 - y samples over the temperature range 4.2 K < T < 300 K. It was shown that the copper NQR line width monotonically increases with decreasing temperature in the below-critical region, resembling temperature behavior of the superconducting gap. The observed dependence is explained by the fact that the energy of a condensate of sliding charge-current states of the charge-density-wave type depends on the phase of order parameter. Calculations show that this dependence appears only at T < Tc. Quantitative estimates of the line broadening at T < Tc. agree with the measurement results. © 2001 MAIK "Nauka/Interperiodica"

Exotic phases of frustrated antiferromagnet LiCu2O2

7Li NMR spectra were measured in a magnetic field up to 17 T at temperatures 5-30 K on single crystalline LiCu2O2. Earlier reported anomalies on magnetization curves correspond to magnetic field values where we observe changes of the NMR spectral shape. For the interpretation of the field and temperature evolutions of our NMR spectra, the magnetic structures were analyzed in the frame of the phenomenological theoretical approach of the Dzyaloshinskii-Landau theory. A set of possible planar and collinear structures was obtained. Most of these structures have an unusual configuration; they are characterized by a two-component order parameter and their magnetic moments vary harmonically not only in direction, but also in size. From the modeling of the observed spectra, a possible scenario of magnetic structure transformations is obtained.Comment: 17 pages, 14 figure

Stripe motion in CuO2 planes of Y1-xPrxBa2Cu3O7 as observed from the Cu(2) quadrupole resonance

The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2-200 K are investigated by a pulsed NQR technique at frequencies of 28-33 MHz. Quantitative analysis of the spectra shows that the shape of the "plane" Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down. © 1997 American Institute of Physics

Cu(2) nuclear resonance evidence for an original magnetic phase in aged 60K-superconductors RBa2Cu3O6+x (R=Tm,Y)

It is widely believed that the long-range antiferromagnetic order in the RBa2Cu3O6+x compounds (R=Y and rare earths except of Ce, Pr, Tb) is totally suppressed for the oxygen index x>0.4 (AFM insulator-metal transition). We present the results of the copper NQR/NMR studies of aged RBa2Cu3O6+x (R=Tm,Y) samples showing that a magnetic order can still be present at oxygen contents x up to at least 0.7 and at temperatures as high as 77K.Comment: 7 pages, 6 figures. Submitted to Phys.Rev.

High-field magnetic structure of the triangular antiferromagnet RbFe(MoO4)2

The magnetic H − T phase diagram of a quasi-two-dimensional antiferromagnet RbFe(MoO4 )2 (S = 5/2) with an equilateral triangular lattice structure is studied with 87Rb NMR and neutron-diffraction techniques. This combination of experimental techniques allows us to determine the ordered components of the magnetic moments on the Fe3+ ions within various high-field phases—the Y, UUD, V, and fan structures, stabilized in the compound by the in-plane magnetic field. It is also established that the transition from the V to the fan phase is of first order, whereas the transition from the fan phase to the polarized paramagnetic phase is continuous. An analysis of the NMR spectra shows that the high-field fan phase of RbFe(MoO4 )2 can be successfully described by a periodic commensurate oscillation of the magnetic moments around the field direction in each Fe3+ layer combined with an incommensurate modulation of the magnetic structure perpendicular to the layers