Conductance properties of rough quantum wires with colored surface disorder

Effects of correlated disorder on wave localization have attracted considerable interest. Motivated by the importance of studies of quantum transport in rough nanowires, here we examine how colored surface roughness impacts the conductance of two-dimensional quantum waveguides, using direct scattering calculations based on the reaction matrix approach. The computational results are analyzed in connection with a theoretical relation between the localization length and the structure factor of correlated disorder. We also examine and discuss several cases that have not been treated theoretically or are beyond the validity regime of available theories. Results indicate that conductance properties of quantum wires are controllable via colored surface disorder.Comment: 19 pages, 7 figure

Deconfinement and Thermodynamics in 5D Holographic Models of QCD

We review 5D holographic approaches to finite temperature QCD. Thermodynamic properties of the "hard-wall" and the "soft-wall" models are derived. Various non-realistic features in these models are cured by the set-up of improved holographic QCD, that we review here.Comment: Invited review paper for Mod. Phys. Let

Engineering nonlinear response of nanomaterials using Fano resonances

We show that, nonlinear optical processes of nanoparticles can be controlled by the presence of interactions with a molecule or a quantum dot. By choosing the appropriate level spacing for the quantum emitter, one can either suppress or enhance the nonlinear frequency conversion. We reveal the underlying mechanism for this effect, which is already observed in recent experiments: (i) Suppression occurs simply because transparency induced by Fano resonance does not allow an excitation at the converted frequency. (ii) Enhancement emerges since nonlinear process can be brought to resonance. Path interference effect cancels the nonresonant frequency terms. We demonstrate the underlying physics using a simplified model, and we show that the predictions of the model are in good agreement with the 3-dimensional boundary element method (MNPBEM toolbox) simulations. Here, we consider the second harmonic generation in a plasmonic converter as an example to demonstrate the control mechanism. The phenomenon is the semi-classical analog of nonlinearity enhancement via electromagnetically induced transparency.Comment: 10 pages, 6 figure

Phenomenology of AdS/QCD and Its Gravity Dual

We construct the dilaton potential in the gravity dual theory of AdS/QCD for the warp factor of Refs.{1,2}. Using this AdS_5-metric with properties similar to QCD, we find that the gravity dual leads to a meaningful gauge coupling in the region between the charmonium and bottonium mass, but differs slightly from QCD in the extreme UV. When we fix the ultraviolet behavior in accord with the beta-function, we can obtain good agreement with the overall heavy quark-antiquark potential. Although the leading order proportional to -\alpha^{4/3}/r differs from perturbative QCD, the full potential agrees quite well with the short distance QCD potential in NNLO.Comment: 42 pages, 13 figures, 1 tabl

Polyakov Loops in Strongly-Coupled Plasmas with Gravity Duals

We study the properties of the Polyakov loop in strongly-coupled gauge plasmas that are conjectured to be dual to five dimensional theories of gravity coupled to a nontrivial single scalar field. We find a gravity dual that can describe the thermodynamic properties and also the expectation value of the Polyakov loop in the deconfined phase of quenched SU(3) QCD up to $3T_c$.Comment: 7 pages, 2 figures, talk presented at the International Conference on Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - oct. 2, 200

A Holographic Model of Strange Metals

We give a review on our recent work arXiv:1006.0779 [hep-th] and arXiv:1006.1719 [hep-th], in which properties of holographic strange metals were investigated. The background is chosen to be anisotropic scaling solution in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC conductivity, the DC Hall conductivity and the AC conductivity are extensively analyzed. We classify behaviors of the conductivities according to the parameter ranges in the bulk theory and characterize conditions when the holographic results can reproduce experimental data.Comment: 34 pages, 15 figures, minor correction

Dressed spectral densities for heavy quark diffusion in holographic plasmas

We analyze the large frequency behavior of the spectral densities that govern the generalized Langevin diffusion process for a heavy quark in the context of the gauge/gravity duality. The bare Langevin correlators obtained from the trailing string solution have a singular short-distance behavior. We argue that the proper dressed spectral functions are obtained by subtracting the zero-temperature correlators. The dressed spectral functions have a sufficiently fast fall-off at large frequency so that the Langevin process is well defined and the dispersion relations are satisfied. We identify the cases in which the subtraction does not modify the associated low-frequency transport coefficients. These include conformal theories and the non-conformal, non-confining models. We provide several analytic and numerical examples in conformal and non-conformal holographic backgrounds.Comment: 51 pages, 2 figure

Holography and Thermodynamics of 5D Dilaton-gravity

The asymptotically-logarithmically-AdS black-hole solutions of 5D dilaton gravity with a monotonic dilaton potential are analyzed in detail. Such theories are holographically very close to pure Yang-Mills theory in four dimensions. The existence and uniqueness of black-hole solutions is shown. It is also shown that a Hawking-Page transition exists at finite temperature if and only if the potential corresponds to a confining theory. The physics of the transition matches in detail with that of deconfinement of the Yang-Mills theory. The high-temperature phase asymptotes to a free gluon gas at high temperature matching the expected behavior from asymptotic freedom. The thermal gluon condensate is calculated and shown to be crucial for the existence of a non-trivial deconfining transition. The condensate of the topological charge is shown to vanish in the deconfined phase.Comment: LaTeX, 61 pages (main body) + 58 pages (appendix), 25 eps figures. Revised version, published in JHEP. Two equations added in Section 7.4; typos corrected; references adde