Splitting of Conduction-Electron Spin Resonance in Potassium

The 0.5-G splitting of the conduction-electron spin resonance in potassium (at 4200 G) observed by Walsh, Rupp, and Schmidt can be quantitatively explained providing the conduction electrons are in a charge-density-wave (CDW) ground state. The Fermi-surface distortion caused by the CDW energy gap leads to an anisotropic conduction-electron $g$ factor depending on the angle between H and the wave vector Q of the CDW. The extremal values of $g$, corresponding to Q ⊥ H and Q∥H, differ by $\left(\frac{3V}{8E_F}\right)\Delta g$, where $\Delta g=-0.0025\mathrm{}$ is the observed $g$ shift. $V$ is the observed threshold energy of the Mayer-El Naby optical-absorption anomaly, and $E_F$ is the Fermi energy. The predicted maximum splitting is 0.56 G. Interpretation of the data requires the sample to have a macroscopic domain structure, caused by thermal stress and plastic flow when the potassium-Parafilm sandwich is cooled to He temperature. The orientation of Q in stress-free regions should be parallel to H. In regions of high stress, Q is presumed perpendicular to the surface, and therefore approximately perpendicular to H.