Suspended Long-Lived NMR Echo in Solids

The Intrinsic Origin of Spin Echoes in Dipolar Solids Generated by Strong Pi Pulses

In spectroscopy, it is conventional to treat pulses much stronger than the linewidth as delta-functions. In NMR, this assumption leads to the prediction that pi pulses do not refocus the dipolar coupling. However, NMR spin echo measurements in dipolar solids defy these conventional expectations when more than one pi pulse is used. Observed effects include a long tail in the CPMG echo train for short delays between pi pulses, an even-odd asymmetry in the echo amplitudes for long delays, an unusual fingerprint pattern for intermediate delays, and a strong sensitivity to pi-pulse phase. Experimen…

Generating Unexpected Spin Echoes in Dipolar Solids with Pi Pulses

NMR spin echo measurements of C-13 in C60, Y-89 in Y2O3, and Si-29 in silicon are shown to defy conventional expectations when more that one pi pulse is used. Multiple pi-pulse echo trains may either freeze our or accelerate the decay of the signal, depending on the pi-pulse phase. Average Hamiltonian theory, combined with exact quantum calculations, reveals an intrinsic cause for these coherent phenomena: the dipolar coupling has a many-body effect during any real, finite pulse.

Few-second-long correlation times in a quantum dot nuclear spin bath probed by frequency-comb NMR spectroscopy

One of the key challenges in spectroscopy is inhomogeneous broadening that masks the homogeneous spectral lineshape and the underlying coherent dynamics. A variety of techniques including four-wave mixing and spectral hole-burning are used in optical spectroscopy while in nuclear magnetic resonance (NMR) spin-echo is the most common way to counteract inhomogeneity. However, the high-power pulses used in spin-echo and other sequences often create spurious dynamics obscuring the subtle spin correlations that play a crucial role in quantum information applications. Here we develop NMR techniques …

NMR Determination of 2D Electron Spin Polarization at $ν=1/2$

Using a `standard' NMR spin-echo technique we determined the spin polarization of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei in the wells. Concentrating on the temperature and magnetic field dependencies of spin polarization at Landau level filling factor $ν=1/2$, we find that the results are described well by a simple model of non-interacting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.

Individual Mechanisms of Nuclear Spin Decoherence in a Nanoscale GaAs NMR Device

We study decoherence of nuclear spins in a nanoscale GaAs device based on resistively detected nuclear magnetic resonance (NMR). We demonstrate how the spin echo technique can be modified for our system, and this is compared to the damping of Rabi-type coherent oscillations. By selectively decoupling nuclear-nuclear and electron-nuclear spin, we determine decoherence rates due to individual mechanisms, namely, direct or indirect dipole coupling between different or like nuclides and electron-nuclear spin coupling. The data reveal that the indirect dipole coupling between Ga and As mediated by …

超导蜿蜒线表面线圈用于纳米级薄膜的核磁共振光谱

Superconducting meander-line surface coil for NMR spectroscopy of nanoscale thin films

本研究提出一种超导蜿蜒线表面线圈，用于提高纳米级薄膜的NMR灵敏度，通过检测硼膜验证了该技术的可行性，为研究原子薄材料提供了新工具。