Coupled quantum wires

We study a set of crossed 1D systems, which are coupled with each other via tunnelling at the crossings. We begin with the simplest case with no electron-electron interactions and find that besides the expected level splitting, bound states can emerge. Next, we include an external potential and electron-electron interactions, which are treated within the Hartree approximation. Then, we write down a formal general solution to the problem, giving additional details for the case of a symmetric external potential. Concentrating on the case of a single crossing, we were able to explain recent experinents on crossed metallic and semiconducting nanotubes [J. W. Janssen, S. G. Lemay, L. P. Kouwenhoven, and C. Dekker, Phys. Rev. B 65, 115423 (2002)], which showed the presence of localized states in the region of crossing.Comment: 11 pages, 10 figure

Infrared spectroscopy of hole doped ABA-stacked trilayer graphene

Using infrared spectroscopy, we investigate bottom gated ABA-stacked trilayer graphene subject to an additional environment-induced p-type doping. We find that the Slonczewski-Weiss-McClure tight-binding model and the Kubo formula reproduce the gate voltage-modulated reflectivity spectra very accurately. This allows us to determine the charge densities and the potentials of the {\pi}-band electrons on all graphene layers separately and to extract the interlayer permittivity due to higher energy bands.Comment: 6 pages, 6 figures Corrected sign of fig 3 and visibilty of fig

Mathematical simulation of water and methanol segregation processes at field preparation of gas condensate

Calculation modulus for water and methanol segregation processes from gas condensate has been developed. Applying the developed technological system the influence of process variables on segregation processes of water and methanol is studied. Modes of operation of liquid separators at which the most efficient segregation of water-methanol solution from unstable condensate occurs are recommende

Effect of processing by femtosecond pulsed laser on mechanical properties of submicrocrystalline titanium

Effect of femtosecond laser processing on mechanical properties of plates made of submicrocrystalline VT1-0 titanium alloy is studied using active deformation and fatigue testing involving cantilever bendin

In-plane optical spectral weight transfer in optimally doped Bi2_{2}Sr2_{2}Ca2_{2}Cu3_{3}O10_{10}

We examine the redistribution of the in-plane optical spectral weight in the normal and superconducting state in tri-layer \bbb (Bi2223) near optimal doping ($T_c$ = 110 K) on a single crystal via infrared reflectivity and spectroscopic ellipsometry. We report the temperature dependence of the low-frequency integrated spectral weight $W(\Omega_c)$ for different values of the cutoff energy $\Omega_c$. Two different model-independent analyses consistently show that for $\Omega_c$ = 1 eV, which is below the charge transfer gap, $W(\Omega_c)$ increases below $T_c$, implying the lowering of the kinetic energy of the holes. This is opposite to the BCS scenario, but it follows the same trend observed in the bi-layer compound \bb (Bi2212). The size of this effect is larger in Bi2223 than in Bi2212, approximately scaling with the critical temperature. In the normal state, the temperature dependence of $W(\Omega_c)$ is close to $T^2$ up to 300 K

Infrared conductivity of hole accumulation and depletion layers in (Ga,Mn)As- and (Ga,Be)As-based electric field-effect devices

We have fabricated electric double-layer field-effect devices to electrostatically dope our active materials, either $x$=0.015 Ga$_{1-x}$Mn$_x$As or $x$=3.2$\times10^{-4}$ Ga$_{1-x}$Be$_x$As. The devices are tailored for interrogation of electric field induced changes to the frequency dependent conductivity in the accumulation or depletions layers of the active material via infrared (IR) spectroscopy. The spectra of the (Ga,Be)As-based device reveal electric field induced changes to the IR conductivity consistent with an enhancement or reduction of the Drude response in the accumulation and depletion polarities, respectively. The spectroscopic features of this device are all indicative of metallic conduction within the GaAs host valence band (VB). For the (Ga,Mn)As-based device, the spectra show enhancement of the far-IR itinerant carrier response and broad mid-IR resonance upon hole accumulation, with a decrease of these features in the depletion polarity. These later spectral features demonstrate that conduction in ferromagnetic (FM) Ga$_{1-x}$Mn$_x$As is distinct from genuine metallic behavior due to extended states in the host VB. Furthermore, these data support the notion that a Mn-induced impurity band plays a vital role in the electron dynamics of FM Ga$_{1-x}$Mn$_x$As. We add, a sum-rule analysis of the spectra of our devices suggests that the Mn or Be doping does not lead to a substantial renormalization of the GaAs host VB

Topological susceptibility in Yang-Mills theory in the vacuum correlator method

We calculate the topological susceptibility of the Yang-Mills vacuum using the field correlator method. Our estimate for the SU(3) gauge group, \chi^{1/4} = 196(7) MeV, is in a very good agreement with the results of recent numerical simulations of the Yang-Mills theory on the lattice.Comment: 5 pages (JETP Letters style

Effective Quark Lagrangian in the Instanton Vacuum with Nonzero Modes Included

A new approach to effective theory of quarks in the instanton vacuum is presented. Exact equations for the quark propagator and Lagrangian are derived which contain contributions of all quark modes with known coefficients. The resulting effective Lagrangian differs from the standard one and resembles that of the Nambu-Jona-Lasinio model.Comment: 5 page

The Missing Link: Magnetism and Superconductivity

The effect of magnetic moments on superconductivity has long been a controversial subject in condensed matter physics. While Matthias and collaborators experimentally demonstrated the destruction of superconductivity in La by the addition of magnetic moments (Gd), it has since been suggested that magnetic fluctuations are in fact responsible for the development of superconducting order in other systems. Currently this debate is focused on several families of unconventional superconductors including high-Tc cuprates, borocarbides as well as heavy fermion systems where magnetism and superconductivity are known to coexist. Here we report a novel aspect of competition and coexistence of these two competing orders in an interesting class of heavy fermion compounds, namely the 1-1-5 series: CeTIn5 where T=Co, Ir, or Rh. Our optical experiments indicate the existence of regions in momentum space where local moments remain unscreened. The extent of these regions in momentum space appears to control both the normal and superconducting state properties in the 1-1-5 family of heavy fermion (HF) superconductors.Comment: 6 pages, 2 figure