Additional Evidence for the Surface Origin of the Peculiar Angular-Dependent Magnetoresistance Oscillations Discovered in a Topological Insulator Bi_{1-x}Sb_{x}

We present detailed data on the unusual angular-dependent magnetoresistance oscillation phenomenon recently discovered in a topological insulator Bi_{0.91}Sb_{0.09}. Direct comparison of the data taken before and after etching the sample surface gives compelling evidence that this phenomenon is essentially originating from a surface state. The symmetry of the oscillations suggests that it probably comes from the (111) plane, and obviously a new mechanism, such as a coupling between the surface and the bulk states, is responsible for this intriguing phenomenon in topological insulators.Comment: 5 pages, 4 figures, Proceedings manuscript for the 19th International Conference on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology (HMF-19

Quasi-persistent currents in the high field phase of alpha-(BEDT-TTF)(2)TlHg(SCN)(4): Evidence for quantum Hall effect

Magnetisation measurements performed on the charge-transfer salt alpha-(BEDT-TTF)(2)TlHg(SCN)(4) in pulsed magnetic fields reveal the existence of eddy current ''resonances'' in the high field state, indicating the presence of deep minima in the transverse magnetoresistivity (or ideal conducting phases). Their behaviour can be explained qualitatively in terms of enhanced conductivity due to the quantum Hall effect, which becomes possible even when quasi-one-dimensional carriers are present

Quasi-persistent currents in the high field phase of α-(BEDT-TTF)2TlHg(SCN)4: evidence for quantum Hall effect

Magnetisation measurements performed on the charge-transfer salt α-(BEDT-TTF)2TlHg(SCN)4 in pulsed magnetic fields reveal the existence of eddy current 'resonances' in the high field state, indicating the presence of deep minima in the transverse magnetoresistivity (or ideal conducting phases). Their behavior can be explained qualitatively in terms of enhanced conductivity due to the quantum Hall effect, which becomes possible even when quasi-one-dimensional carriers are present

Pulsed-magnetic-field measurements of Hall potential oscillations in alpha-(BEDT-TTF)(2)TlHg(SCN)(4) within the quantum Hall regime

Using a variant of the Corbino geometry in pulsed magnetic fields of up to 60 T, we have made direct measurements of the Hall potential in α-(BEDT-TTF)2TIHg(SCN)4 within the quantum Hall regime. This method enables the in-plane components of the resistivity tensor, which are normally very difficult to measure, to be investigated and the nonlinear behavior of the sample's I-V characteristics to be studied. It is found that an increasing probability of magnetic breakdown at higher fields leads to a degradation of the quantum Hall effect. ©1999 The American Physical Society

Resonant magnetoabsorption of millimeter-wave radiation in the quasi-two-dimensional organic metals alpha -(BEDT-TTF)2MHg(SCN)4 (M=K,Tl).

The magnetoabsorption of millimeter-wave radiation by single crystals of the organic metals α-(BEDT-TTF)2TlHg(SCN)4 and α-(BEDT-TTF)2KHg(SCN)4 has been studied in the frequency range 30-120 GHz. The experiments reveal two dominant contributions to the magnetoabsorption spectra. The first is interpreted as the cyclotron resonance of two-dimensional carriers, and is characterized by broad lines (linewidth/magnetic field ΔB/B∼0.5-1). In addition to a resonance exhibiting a cyclotron mass mc∼2.8m0, there are two further lines corresponding to frequency-dependent cyclotron masses in the ranges mc∼(1-1.5)m0 and mc∼(0.5-0.8)m0. This frequency dependence is believed to result from many-body effects. The second contribution to the magnetoabsorption is formed by a series of narrow lines with ΔB/B∼0.03-0.1 and amplitudes 5-10 times smaller than the features interpreted as cyclotron resonances. These narrow lines are attributed to a superposition of modes due to antiferromagnetic resonance and conduction-electron-spin resonance (ESR). The feature characteristic of antiferromagnetic resonance is the presence of a mode with a frequency that decreases with increasing magnetic field. The magnetoabsorption structure attributed to ESR consists of a relatively broad maximum upon which a sharp dip is superimposed. This behavior is believed to be analogous to the resonant transparency observed in thin metallic films undergoing ESR

A Coherent Three-Dimensional Fermi Surface in a High-Transition-Temperature Superconductor

All conventional metals are known to possess a three-dimensional Fermi surface, which is the locus in reciprocal space of the long-lived electronic excitations that govern their electronic properties at low temperatures. These excitations should have well-defined momenta with components in all three dimensions. The high-transition-temperature (high-T-c) copper oxide superconductors have unusual, highly two-dimensional properties above the superconducting transition(1). This, coupled with a lack of unambiguous evidence for a three-dimensional Fermi surface, has led to many new and exotic models for the underlying electronic ground state(2). Here we report the observation of polar angular magnetoresistance oscillations(3) in the overdoped superconductor Tl2Ba2CuO6+delta in high magnetic fields, which firmly establishes the existence of a coherent three-dimensional Fermi surface. Analysis of the oscillations reveals that at certain symmetry points, however, this surface is strictly two-dimensional. This striking form of the Fermi surface topography, long-predicted by electronic band structure calculations(4), provides a natural explanation for a wide range of anisotropic properties both in the normal(5,6) and superconducting states(7-9). Our data reveal that, despite their extreme electrical anisotropy, the high-T-c materials at high doping levels can be understood within a framework of conventional three-dimensional metal physics