Microwave properties of potassium caused by the charge-density-wave broken symmetry
Abstract
The microwave surface resistance of potassium in a perpendicular magnetic field, measured by C. C. Grimes in 1969, has never been completely explained. The sharp cyclotron resonance peak (at a magnetic field $H\sb{c}$) is caused by a small cylindrical section of Fermi surface created by the charge-density wave (CDW) minigaps, having periodicities $\vec K\sb{n} = (n + 1)\vec Q - n\vec G\sb{110}.$ The shape of the observed resonance requires a tilt of the CDW vector $\vec Q$ away from (110), predicted by Giuliani and Overhauser in 1979. An abrupt drop of the surface resistance for $\vert H\vert > \vert H\sb{c}\vert$ is caused by the heterodyne gaps, which have periodicities $\vec K\sb{n} = n(\vec G\sb{110} - \vec Q)$. These very small gaps, which begin to undergo magnetic breakdown for fields $H > 1T,$ interrupt the cyclotron motion of equatorial orbits. The abrupt drop in surface resistance for $\vert H\vert > \vert H\sb{c}\vert$ is caused by a partial loss of carrier effectiveness for electrons having velocities nearly parallel to the surface. Microwave transmission through potassium by Dunifer et al. shows five signals. They are Gantmakher-Kaner (GK) oscillations, conduction-electron spin resonance, high-frequency oscillations, cyclotron resonance, and cyclotron-resonance subharmonics. Only the spin resonance has been successfully explained using a free electron model. However, such a model predicts GK oscillations which are too large by several orders of magnitude. Lacueva and Overhauser have shown that CDW energy gaps which cut through the Fermi surface reduce the GK signal. The high-frequency oscillations were shown to result from Landau-level quantization in a Fermi-surface cylinder created by the CDW. In this study we show that oscillatory motion, parallel to the field, of electrons in a tilted cylinder cause the cyclotron-resonance transmission. This signal and its subharmonics would be completely absent without the tilt. Consequently, four of the five transmission signals require a CDW broken symmetry.
Degree
Ph.D.
Advisors
Overhauser, Purdue University.
Subject Area
Condensation
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.