The importance of edge states in the quantum Hall regime of the organic conductor

Abstract

We report measurements of the longitudinal magnetoresistance and magnetization of in pulsed magnetic fields of up to 50 T and temperatures down to 400 mK, using samples of different purity. Below 2 K the amplitude of the Shubnikov - de Haas oscillations in is found to decrease dramatically with falling temperature. This effect is shown to coincide with quasipersistent eddy current resonances in the magnetization, which are a signature of the quantum Hall effect. Evidence is provided for the existence of a novel interplane conduction mechanism involving highly metallic edge states with supressed scattering at the surface of the sample (a so-called `chiral Fermi liquid'), operational when the chemical potential is between Landau levels in the bulk of the material.

Pulsed-magnetic-field measurements of Hall potential oscillations inα−(BEDT−TTF)2TlHg(SCNHonold1, Harrison2, Singleton3 et al. 1999Phys. Rev. B14490View full textAdd to dashboardCite

“…3,4 While is between Landau levels, the carriers involved in charge transport cannot perform the closed orbits necessary to cause changes in the Hall resistivity xy , which therefore remains ''frozen'' at a constant value; 5,6 it has been shown that the plateaux in xy thus produced correspond to a manifestation of the quantum Hall effect ͑QHE͒. [6][7][8][9][10][11] At the same fields, the resistivity component ʈ Ϸ 1 2 ( xx ϩ yy ) exhibits deep minima 7,9,10 and the interplane resistivity zz shows large maxima. 4 In this paper, we describe measurements of the Hall potential in ␣-(BEDT-TTF) 2 TlHg(SCN) 4 in this high-field range, made using an analog of the Corbino geometry ͑Fig.…”

“…9 The current saturation is thought to be due to mechanisms such as Zener tunneling between Landau levels at the sample edges. 10,23 This leads to a dissipation of the induced current and thus to breakdown of the QHE. 9,10 The maximum Hall potential energy drop eV H between the center and the perimeter of the sample is therefore limited by the Landau-level spacing ប c .…”

“…Figure 1͑a͒ shows that between ϳ27 T and 37 T, the values of the peaks of V H coincide with the cyclotron energy 24 ប c divided by e. This is in agreement with estimates of the peak circulating current made in magnetization experiments. 9,10 The effects of the extreme nature of the electronic DOS ͑almost ␦-function-like Q2D Landau levels with a smooth background of Q1D states͒ will be weakened by increasing the temperature; the consequent broadening of the Fermi-Dirac distribution function around will allow electrons to access some of the Q2D states, even when is between Landau levels. 4 Thus, the minima in ʈ will be much more shallow, 6,10 greatly restricting the peak current that can flow in the sample.…”

Destabilization of a Charge-Density Wave by an Oscillatory Chemical Potential

“…However, since both the gapped one-particle DOS and the derivative of the Fermi-Dirac (FD) distribution function are symmetric aboutm 6 h, both h andm (irrespective of sign) have an equivalent detrimental effect on the stability of the CDW condensate. Given that the magnitude ofm ϳ 1 2h v c ϳ 1 meV [20,21] at fields of 23 T in the M K salt (wherehv c is the cyclotron energy of the 2D pocket) is directly comparable with D 0 ϳ 1.2 meV (estimated using the BCS relation), m should clearly have quite a pronounced effect on these materials. Furthermore, a large body of papers, concerning measurements of quantum oscillatory effects and angular magnetoresistance oscillations within the low temperature, low magnetic field (LTLF) phase of these salts, support a picture in which the CDW (or SDW) is commensurate throughout [19,22,23].…”

Magnetoquantum oscillations in two-dimensional electron systems with Lorentzian broadened spin-split Landau levels and background electron reservoir states

“…Metals with a quasi-two-dimensional ͑2D͒ Fermi surface ͑such as organic metals 4,5 ͒ may serve as model crystals due to the relatively simple picture of their magnetoquantum oscillations. Not only the fundamental frequency and amplitude ͑cyclotron mass͒ but also the precise wave form of oscillations has become the object of investigations, [6][7][8] including magnetoquantum oscillations with spin-split structure. [9][10][11][12][13][14] These investigations give valuable information about the more complex Fermi surface in quasi-2D organic metals containing both closed and open parts.…”