Magnetic-field-induced Stoner transition in a dilute quantum Hall system

In a recent paper [Phys.Rev.B.\textbf{84}, 161307 (2011)], experimental data on spin splitting in the integer quantum Hall effect has been reported in a high mobility dilute 2D electron gas with electron density as low as 0.2 $\times$ 10$^{11}$ cm $^{-2}$. In this work, we show that an excellent \emph{quantitative} description of these data can be obtained within the model of the magnetic-field-induced Stoner transition in the quantum Hall regime. This provides a powerful tool to probe the non-trivial density dependance of electron-electron interactions in the dilute regime of the 2D electron gas

Quasiparticle density of states in Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} single crystals probed using tunneling spectroscopy at ultra-low temperatures in high magnetic fields

Break-junction tunneling spectroscopy at temperatures 30-50 mK in high magnetic field is used to directly probe the quasiparticle density of states within the energy gap in a single crystal Bi2212 high-$T_c$ superconductor. The measured tunneling conductances $dI/dV(V)$ in the subgap region have a zero flat region with no evidence for a linear increase of the density of states with voltage. A number of tunnel break-junctions exhibited $dI/dV(V)$ curves with a second energy gap structure at the average magnitude 2$\Delta _{p-p}/e=13$ mV. Our data cannot be explained by either a pure $s$ pairing or a pure $d_{x^2-y^2}$ pairing

A consistent interpretation of the low temperature magneto-transport in graphite using the Slonczewski--Weiss--McClure 3D band structure calculations

Magnetotransport of natural graphite and highly oriented pyrolytic graphite (HOPG) has been measured at mK temperatures. Quantum oscillations for both electron and hole carriers are observed with orbital angular momentum quantum number up to $N\approx90$. A remarkable agreement is obtained when comparing the data and the predictions of the Slonczewski--Weiss--McClure tight binding model for massive fermions. No evidence for Dirac fermions is observed in the transport data which is dominated by the crossing of the Landau bands at the Fermi level, corresponding to $dE/dk_z=0$, which occurs away from the $H$ point where Dirac fermions are expected.Comment: 3 figure

Dirac fermions at the H point of graphite: Magneto-transmission studies

We report on far infrared magneto-transmission measurements on a thin graphite sample prepared by exfoliation of highly oriented pyrolytic graphite. In magnetic field, absorption lines exhibiting a blue-shift proportional to sqrtB are observed. This is a fingerprint for massless Dirac holes at the H point in bulk graphite. The Fermi velocity is found to be c*=1.02x10^6 m/s and the pseudogap at the H point is estimated to be below 10 meV. Although the holes behave to a first approximation as a strictly 2D gas of Dirac fermions, the full 3D band structure has to be taken into account to explain all the observed spectral features.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Second order resonant Raman scattering in single layer tungsten disulfide (WS2_{2})

Resonant Raman spectra of single layer WS$_{2}$ flakes are presented. A second order Raman peak (2LA) appears under resonant excitation with a separation from the E$^{1}_{2g}$ mode of only $4$cm$^{-1}$. Depending on the intensity ratio and the respective line widths of these two peaks, any analysis which neglects the presence of the 2LA mode can lead to an inaccurate estimation of the position of the E$^{1}_{2g}$ mode, leading to a potentially incorrect assignment for the number of layers. Our results show that the intensity of the 2LA mode strongly depends on the angle between the linear polarization of the excitation and detection, a parameter which is neglected in many Raman studies.Comment: 6 pages, 4 figure

Novel metallic and insulating states at a bent quantum Hall junction

A non-planar geometry for the quantum Hall (QH) effect is studied, whereby two quantum Hall (QH) systems are joined at a sharp right angle. When both facets are at equal filling factor nu the junction hosts a channel with non-quantized conductance, dependent on nu. The state is metallic at nu = 1/3, with conductance along the junction increasing as the temperature T drops. At nu = 1, 2 it is strongly insulating, and at nu = 3, 4 shows only weak T dependence. Upon applying a dc voltage bias along the junction, the differential conductance again shows three different behaviors. Hartree calculations of the dispersion at the junction illustrate possible explanations, and differences from planar QH structures are highlighted.Comment: 5 pages, 4 figures, text + figs revised for clarit