Room-Temperature Quantum Hall Effect in Graphene

The quantum Hall effect (QHE), one example of a quantum phenomenon that occur on a truly macroscopic scale, has been attracting intense interest since its discovery in 1980 and has helped elucidate many important aspects of quantum physics. It has also led to the establishment of a new metrological standard, the resistance quantum. Disappointingly, however, the QHE could only have been observed at liquid-helium temperatures. Here, we show that in graphene - a single atomic layer of carbon - the QHE can reliably be measured even at room temperature, which is not only surprising and inspirational but also promises QHE resistance standards becoming available to a broader community, outside a few national institutions.Comment: Published in Science online 15 February 200

Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}

We measure the normal-state in-plane resistivity of La-doped Bi-2201 single crystals at low temperatures by suppressing superconductivity with 60-T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR

Cooper pair delocalization in disordered media

We discuss the effect of disorder on the coherent propagation of the bound state of two attracting particles. It is shown that a result analogous to the Anderson theorem for dirty superconductors is also valid for the Cooper problem, namely, that the pair wave function is extended beyond the single-particle localization length if the latter is large. A physical justification is given in terms of the Thouless block-scaling picture of localization. These arguments are supplemented by numerical simulations. With increasing disorder we find a transition from a regime in which the interaction delocalizes the pair to a regime in which the interaction enhances localization.Comment: 5 pages, RevTex with 2 figures include

Charge and spin inhomogeneity as a key to the physics of the high Tc cuprates

We present a coherent scenario for the physics of cuprate superconductors, which is based on a charge-driven inhomogeneity, i.e. the ``stripe phase''. We show that spin and charge critical fluctuations near the stripe instability of strongly correlated electron systems provide an effective interaction between the quasiparticles, which is strongly momentum, frequency, temperature and doping dependent. This accounts for the various phenomena occurring in the overdoped, optimally and underdoped regimes both for the normal and the superconductive phase.Comment: 6 pages, 1 enclosed figure, proceedings of LT2

Magnetospectroscopy of symmetric and anti-symmetric states in double quantum wells

The experimental results obtained for the magneto-transport in the InGaAs/InAlAs double quantum wells (DQW) structures of two different shapes of wells are reported. The beating-effect occurred in the Shubnikov-de Haas (SdH) oscillations was observed for both types of the structures at low temperatures in the parallel transport when magnetic field was perpendicular to the layers. An approach to the calculation of the Landau levels energies for DQW structures was developed and then applied to the analysis and interpretation of the experimental data related to the beating-effect. We also argue that in order to account for the observed magneto-transport phenomena (SdH and Integer Quantum Hall effect), one should introduce two different quasi-Fermi levels characterizing two electron sub-systems regarding symmetry properties of their states, symmetric and anti-symmetric ones which are not mixed by electron-electron interaction.Comment: 20 pages, 20 figure

Only Fermi-Liquids are Metals

Any singular deviation from Landau Fermi-liquid theory appears to lead, for arbitrarily small concentration of impurities coupling to a non-conserved quantity, to a vanishing density of states at the chemical potential and infinite resistivity as temperature approaches zero. Applications to copper-oxide metals including the temperature dependence of the anisotropy in resistivity, and to other cases of non Fermi-liquids are discussed.Comment: 11 pages,revtex, 1 Postscript figur