Quantum spin dynamics

Abstract:

We experimentally demonstrate a mechanism for a new kind of magnetic resonance, the Fermi-surface traversal resonance (FTR). This is caused by the periodic traversal of carriers across quasi-one-dimensional (Q1D) sections of Fermi surface (FS) in an external magnetic field. Owing to the warping of the Q1D Fermi sheets, the real space velocities of the carriers oscillate as they cross the FS, generating resonances in the high frequency conductivity of the material. The results contain information about the FS, including the direction and harmonic content of the warping components. Using a rotating resonant-cavity system, FTRs have been observed in α-(BEDT-TTF)2 KHg(SCN)4. © 1998 The American Physical Society.

Abstract:

The fabrication of air-filled rectangular metal-pipe waveguide using a lithographically-based technique has recently been reported. This type of waveguide, together with other passive components such as antennas, couplers, mixers and filters may offer a realistic route to terahertz frequency integrated circuits in view of the compatibility of the fabrication technique with those of standard semiconductor processing. In this contribution, we report the fabrication of a range of waveguide components for operation at frequencies of up to 300 GHz. These measurements represent the highest frequency characterisation study so far reported for a micromachined passive structure of this type and provide proof of TE10 propagation with the expected cut-off frequency. Numerous measurements have been taken using G-band (WR-5) guide which show an attenuation loss of approximately 0.6 dB per guide wavelength at 200 GHz. This low value of attenuation shows that these micromachined waveguide are viable components for use in integrated circuits at terahertz frequencies. The insertion loss repeatability (due to mismatch effects at the ports of the waveguides) has been measured and has been shown to be better than +/-0.5 dB. Preliminary results are presented for J-band (WR-3) waveguide which clearly shows the cut off frequency.

Abstract:

We present the results of a study of the millimetre-wave response of the organic metal alpha-(BEDT-TTF)(2)NH4Hg(SCN)(4), between 500 mK and 4.2 K and in magnetic fields of up to 17 T. Two relatively broad features are interpreted as a two dimensional (2D) cyclotron resonance (CR) with a CR mass m(2D)(CR) = 1.35 +/- 0.1 m(e), and a 1D CR with CR mass m(1D)(CR) = 0.85 +/- 0.05 m(e). Conduction electron spin resonance and magnetic quantum oscillations are also observed. Analysis of the quantum oscillations yields an effective mass of m(RF)* = 2.7 +/- 0.2 m(e).

Abstract:

Electrons in cyclotron orbits around closed pockets in the Fermi surfaces of organic metals possess an oscillating real-space velocity. Higher harmonics of this real-space velocity lead to predicted cyclotron resonances additional to those normally expected. We calculate these resonances semiclassically using the Boltzmann transport equation. These higher harmonics are expected to occur remarkably often, and we show that they are found even in a very simple tight-binding model. A similar effect occurs in quasi-one-dimensional Fermi surfaces which are highly corrugated and in this case the oscillating part of the real-space velocity as it traverses the Fermi surface can couple directly to the microwave frequency. © 1997 The American Physical Society.