Guiding and Trapping of Electron Spin Waves in Atomic Hydrogen Gas

We present a high magnetic field study of electron spin waves in atomic hydrogen gas compressed to high densities of $\sim {10}^{18}{\mathrm{cm}}^{-3}$ at temperatures ranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by the identical spin rotation effect with strong dependence on the spatial profile of the polarizing magnetic field. We demonstrate confinement of these modes in regions of strong magnetic field and manipulate their spatial distribution by changing the position of the field maximum.

Figure 1

(a) Schematic drawing of the sample cell showing the SV, KT, liquid-helium volumes (l-He), FPR, and epoxy structures (E). (b) Magnetic field inhomogeneity due to magnetized epoxy. The field amplitude in the top of SV is shown as a color map, dark red (dark) corresponding to the strongest and yellow (light) to the weakest field. Axial ($z$) and radial ($r$) cuts of the field profile through the field maximum are also shown for three different additional linear gradient values: $-1.7$ (red/dark), $-0.85$ (green/intermediate), and $0(\mathrm{\text{blue}}/\mathrm{\text{light}})\mathrm{G}/\mathrm{mm}$.

Figure 2

ESR absorption spectra for different values of axial magnetic field gradient. The resonance frequency is fixed and magnetic field is swept through the resonance. The regions of the sample volume located in larger local fields will get in resonance at smaller sweep field. The direction of the field axis is reversed to get the local field increasing from left to right. Inset: peak (ii) position as a function of $G_z$.

Figure 3

ESR absorption spectra observed for samples $G_z=-4\mathrm{G}/\mathrm{mm}$. Dotted line: the simulated contribution $F(h)$ of spin waves to the ESR absorption. In the inset the orientations of the potential $U(z)$ (thick solid line), a spin wave mode $S_{+}(z)$, and the evanescent field $H_1^2(z)$ are shown emphasizing the upper part of the sample volume.

Figure 4

Positions of spin wave peaks for samples in large negative magnetic field gradients of $-4\mathrm{G}/\mathrm{mm}$ as functions of H gas density.