Magic Angle Effects of One-Dimensional Axis Conductivity in Quasi-One-Dimensional Conductors

Abstract

In quasi-one-dimensional conductors, the conductivity in both one-dimensional axis and interchain direction shows peaks when magnetic field is tilted at the magic angles in the plane perpendicular to the conducting chain. Although there are several theoretical studies to explain the magic angle effect, no satisfactory explanation, especially for the one-dimensional conductivity, has been obtained. We present a new theory of the magic angle effect in the one-dimensional conductivity by taking account of the momentum-dependence of the Fermi velocity, which should be large in the systems close to a spin density wave instability. The magic angle effect is explained in the semiclassical equations of motion, but neither the large corrugation of the Fermi surface due to long-range hoppings nor hot spots, where the relaxation time is small, on the Fermi surface are required.PACS numbers: 74.70. Kn, 75.30.Fv, Quasi-one-dimensional organic conductors show a lot of interesting phenomena, such as unconventional superconductivity, spin density wave (SDW), field-induced spin density wave, quantum Hall effect, etc [1]. By studying the interaction of electrons with impurities as well as interaction between electrons Lebed and Bak [2] have predicted that the resistance, R xx , has peaks at the magic angles θ = tan, where p and q are mutually prime integers and b and c are lattice constants, when the magnetic field is rotated in the plane perpendicular to the most conducting a axis. Experimentally, dips, instead of peaks, of the resistance at the magic angles are observed in both R xx and R zz in various quasi-one-dimensional organic conductors, (TMTSF) Other angle dependences of the magnoresistance have also been observed in quasi-two-dimensional conductors [12,13,14], and in quasi-one-dimensional conductors with rotating magnetic field in the a-c plane [15] and in the a-b plane [16]. These angle dependences are explained in the semiclassical theory [15,16,17,18] and they are used as powerful tools to observe the shape of the Fermi surface in low-dimensional systems.For MAE, however, no complete explanation has been given yet, although there exit several theories [19,20,21,22,23,24,25,26,27,28]. Interesting idea of the magnetic-field-induced confinement [22] has been proposed to explain MAE. Difference between the ground states at the magic angles and at other directions of the magnetic field is observed by the metallic and nonmetallic temperature dependence of the resistance [6]. In recent NMR experiment [29], however, no evidence for the change of the excitation spectrum at the magic angles has been obtained. This fact suggests that semiclassical approach, or equivalently Green function approach using the linearized k x dispersion, can be applied in these systems. Indeed, MAE can be explained qualitatively in the semiclassical theory. By using the semiclassical equations of motion for the noninteracting electrons in the tilted magnetic field, Osada et al. [19] have shown that the conductivity in the z axis σ zz shows peaks a...

Angle-dependent magneto-resistance in the quasi-one-dimensional system

“…However, these peaks are not large enough to explain the observed peaks [1,2]. The electron correlation is expected to play an important role in the magic angle effect in s xx as we have considered previously [6,7]. (10) is limited to À5om; no5.…”

“…We have shown the large peaks in s xx in a simple model [6]. We have also shown that in the random phase approximation the relative height of each peaks is changed by t and v x which depend on k y and k z due to electron interaction [7].…”

“…Recently, we have proposed that the magic angle effect in s xx is caused by the k y -and k z -dependences of v x due to the electron correlation [6,7]. We have shown the large peaks in s xx in a simple model [6].…”

Effects of Electron Correlation near Spin-Density-Wave on Angle Dependence of Magnetoconductivity

“…8 It is found that the angle dependence of 1D axis magnetoconductivity (σ xx ) appears when a spot of slow or fast velocity exists in the momentum space of the 1D axis velocity. 9 The result in this simple model indicates the possibility that the change in velocity near SDW causes the strong angle dependence in σ xx .…”