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Application of Nuclear Magnetic Resonance in pulsed high-field magnets to high-Tc superconductors

At LNCMI efforts have been performed in order to introduce Nuclear Magnetic Resonance (NMR) in pulsed high-field magnets. Since pulsed fields of up to 100 T have been reported while the highest continuous fields don’t exceed 45 T, the introduction of NMR in pulsed fields potentially allows to investigate high-Tc superconductors in temperature and doping regions formerly inaccessible for NMR experiments.

In fig. (left) the methodology of NMR in pulsed field is explained. During the field pulse RF pulses are applied to the resonant circuit containing the sample coil. Every time the current magnetic field matches the Larmor frequency f0\propto B0 a NMR signal can be detected. The influence of the changing field on NMR spectra can be removed in retrospect applying deconvolution techniques.

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Fig. Left: Time profile of the magnetic field pulse and the voltage detected at the NMR receiver channel Rx. The red line indicates the magnetic field value which corresponds to the irradiated frequency f0 and the gyro magnetic ratio \gamma. Right: Accumulated and partial Fourier spectra of the four detected NMR signals. The numbers in the legend represent the segment number, where each segment contains one Hahn echo sequence. The field decreases from segment 16 to 19 with a rate of about 0.2 kT/s.

Recently we successfully performed 63Cu-NMR experiments on an YBaCuO6.51 single crystal. During a field pulse with a maximum of 47 T, a RF pulse train of Hahn echo sequences (first pulse 0.8 µs, echo time 3.9 µs, second pulse 1.6 µs) with a period of 200 µs was irradiated. Sample temperature was 2.5 K and the magnetic field was parallel to the c-axis. Slightly after the field maximum at a field change rate of 0.2 kT/s we recorded echoes in four neighboring segments. After deconvolution and Fourier transformation the spectrum in fig. (right) could be constructed. It can be identified with the 63Cu main line (compare [1]).

These results represent a proof of concept regarding the potential of NMR in pulsed fields for the investigation of the low-temperature normal state of cuprates.

References

1. T. Wu, H. Mayaffre, S. Krämer, M. Horvatić, C. Berthier, W. N. Hardy, R. Liang, D. A. Bonn and M.-H. Julien, Magnetic-field-induced charge-stripe order in the high-temperature superconductor YBa2Cu3Oy, Nature, 477, 191-194

Contact

Holger.Stork@lncmi.cnrs.fr