Non trivial critical exponents for finite temperature chiral transitions at fixed total fermion number

We analyze the finite temperature chiral restoration transition of the $(D=d+1)$-dimensional Gross-Neveu model for the case of a large number of flavors and fixed total fermion number. This leads to the study of the model with a nonzero imaginary chemical potential. In this formulation of the theory, we have obtained that, in the transition region, the model is described by a chiral conformal field theory where the concepts of dimensional reduction and universality do apply due to a transmutation of statistics which makes fermions act as if they were bosons, having zero energy. This result should be generic for theories with dynamical symmetry breaking, such as Quantum Chromodynamics.Comment: 14 pages Latex, no figures, final version to be published in Phys. Lett.

Tailoring The Interface Using Thiophene Small Molecules In Tio 2/p3ht Hybrid Solar Cells

In this paper we focus on the effect of carboxylated thiophene small molecules as interface modifiers in TiO 2/P3HT hybrid solar cells. Our results show that small differences in the chemical structure of these molecules, for example, the presence of the -CH 2- group in the 2-thiopheneacetic acid (TAA), can greatly increase the TiO 2 surface wettability, improving the TiO 2/polymer contact. This effect is important to enhance exciton splitting and charge separation. This journal is © 2012 the Owner Societies.14341199011993Huang, Y.-C., Hsu, J.-H., Liao, Y.-C., Yen, W.-C., Li, S.-S., Lin, S.-T., Chen, C.-W., Su, W.-F., (2011) J. Mater. Chem., 21, p. 4450Bouclé, J., Ravirajan, P., Nelson, J., (2007) J. Mater. Chem., 17, p. 3141Bhongale, C.J., Thelakkat, M., (2010) Sol. Energy Mater. Sol. Cells, 94, p. 817Bolognesi, M., Sánchez-Díaz, A., Ajuria, J., Pacios, R., Palomares, E., (2011) Phys. Chem. Chem. Phys., 13, p. 6105Arici, E., Meissner, D., Schaffler, F., Sariciftci, N.S., (2003) Int. J. Photoenergy, 5, p. 199Arici, E., Sariciftci, N.S., Meissner, D., (2003) Adv. Funct. Mater., 13, p. 165De Freitas, J.N., Grova, I.R., Akcelrud, L.C., Arici, E., Sariciftcic, N.S., Nogueira, A.F., (2010) J. Mater. Chem., 20, p. 4845Yella, A., Lee, H.-W., Tsao, H.N., Yi, C., Chandiran, A.K., Nazeeruddin, M.K., Diau, E.W.-G., Grätzel, M., (2011) Science, 334, p. 629Yu, Q., Wang, Y., Yi, Z., Zu, N., Zhang, J., Zhang, M., Wang, P., (2010) ACS Nano, 4, p. 6032Lin, Y.-Y., Chu, T.-H., Li, S.-S., Chuang, C.-H., Chang, C.-H., Su, W.-F., Chang, C.-P., Chen, C.-W., (2009) J. Am. Chem. Soc., 131, p. 3644Sun, Z., Li, J., Liu, C., Yang, S., Yan, F., (2011) Adv. Mater., 23, p. 3648Coakley, K.M., Srinvasan, B.S., Ziebarth, J.M., Goh, C., Liu, Y.X., McGehee, M.D., (2005) Adv. Funct. Mater., 15, p. 1927Huang, Y.-C., Yen, W.-C., Liao, Y.-C., Yu, Y.-C., Hsu, C.-C., Ho, M.-L., Chou, P.-T., Su, W.-F., (2010) Appl. Phys. Lett., 96, p. 123501Zhang, W., Zhu, R., Li, F., Wang, Q., Liu, B., (2011) J. Phys. Chem. C, 115, p. 7038Johansson, E.M.J., Scholin, R., Siegbahn, H., Hagfeldt, A., Rensmo, H., (2011) Chem. Phys. Lett., 515, p. 146Ravirajan, P., Peiró, A.M., Nazeeruddin, M.K., Grätzel, M., Bradley, D.D.C., Durrant, J.R., Nelson, J., (2006) J. Phys. Chem. B, 110, p. 7635Weickert, J., Dunbar, R.B., Hesse, H.C., Wiedemann, W., Mende, L.S., (2011) Adv. Mater., 23, p. 1810Chang, J.A., Rhee, J.H., Im, S.H., Lee, Y.H., Kim, H.-J., Seok, S.I., Nazeeruddin, M.K., Gratzel, M., (2010) Nano Lett., 10, p. 2609Jiang, X., Karlsson, K.M., Gabrielsson, E., Johansson, E.M.J., Quintana, M., Karlsson, M., Sun, L., Hagfeldt, A., (2011) Adv. Funct. Mater., 21, p. 2944Snaith, H.J., Moule, A.J., Klein, C., Meerholz, K., Friend, R.H., Grätzel, M., (2007) Nano Lett., 7, p. 3372Weickert, J., Auras, F., Bein, T., Mende, L.S., (2011) J. Phys. Chem. C, 115, p. 15081Liu, Y., Scully, S.R., McGehee, M.D., Liu, J., Luscombe, C.K., Frechet, J.M.J., Shaheen, S.E., Ginley, D.S., (2006) J. Phys. Chem. B, 110, p. 3257Chang, Y.-M., Su, W.-F., Wang, L., (2008) Macromol. Rapid Commun., 29, p. 1303Cantu, M.L., Chafiq, A., Faissat, J., Valls, I.G., Yu, Y., (2011) Sol. Energy Mater. Sol. Cells, 95, p. 1362Jiang, K.-J., Manseki, K., Yu, Y.-H., Masaki, N., Suzuki, K., Suzuki, Y.-L., Yanagida, S., (2009) Adv. Funct. Mater., 19, p. 2481Goh, C., Scully, S.R., McGehee, M.D., (2007) J. Appl. Phys., 101, p. 114503Krüger, J., Bach, U., Grätzel, M., (2000) Adv. Mater., 12, p. 447Montanari, I., Nogueira, A.F., Nelson, J., Durrant, J.R., Winder, C., Loi, M.A., Sariciftci, N.S., Brabec, C., (2002) Appl. Phys. Lett., 81, p. 3001Nogueira, A.F., Montanari, I., Nelson, J., Brabec, C., Sariciftci, N.S., Durrant, J.R., (2003) J. Phys. Chem., 107, p. 1567Haque, S.A., Palomares, E., Cho, B.M., Green, A.N.M., Hirata, N., Klug, D.R., Durrant, J.R., (2005) J. Am. Chem. Soc., 127, p. 3456Clifford, J.N., Palomares, E., Nazeeruddin, M.K., Grätzel, M., Nelson, J., Li, X., Long, J., Durrant, J.R., (2004) J. Am. Chem. Soc., 126, p. 5225Bouclé, J., Chyla, S., Shaffer, M.S.P., Durrant, J.R., Bradley, D.D.C., Nelson, J., (2008) Adv. Funct. Mater., 18, p. 62

Critical behavior of Ginzburg-Landau model coupled to massless Dirac fermions

We point out interesting effects of additional massless Dirac fermions with N_F colors upon the critical behavior of the Ginzburg-Landau model. For increasing N_F, the model is driven into the type II regime of superconductivity. The critical exponents are given as a function of N_F.Comment: RevTex4, 4 pages, 1 figure; author information and latest update to this paper at http://www.physik.fu-berlin.de/~kleinert/institution.html; version 2: new references and comments on chiral symmetry breaking adde

Incorporation Of Nanocrystals With Different Dimensionalities In Hybrid Tio2/p3ht Solar Cells

We investigate the effect of TiO2 nanoparticles-nanospheres and nanorods-inserted in the poly(3-hexylthiophene) (P3HT) matrix of TiO2?P3HT inverted hybrid solar cells. X-ray diffraction, high-resolution transmission electron microscopy, small-angle x-ray scattering, photoluminescence, and photoelectrochemical experiments were employed to investigate the structure, morphology, and photoactivity of TiO2 nanoparticles modified with 2-thiopheneacetic acid, mixed or not with P3HT. Both TiO2 nanospheres and TiO2 nanorods presented a good dispersion in the polymer matrix. The incorporation of TiO2 nanospheres and nanorods has improved the photocurrent generation, and devices with efficiency values up to 1.35% were obtained. Our results reveal that the nanoscale morphology enables an enhanced interfacial area for exciton dissociation. In particular, the nanospheres contribute with their high specific area, and the nanorods contribute with their high aspect ratio.51Lee, C.-K., Pao, C.-W., Chen, C.-W., Correlation of nanoscale organizations of polymer and nanocrystals in polymer/inorganic nanocrystal bulk heterojunction hybrid solar cells: Insights from multiscale molecular simulations (2013) Energy Environ. Sci., 6, pp. 307-315Huynh, W.U., Dittmer, J.J., Alivisatos, A.P., Hybrid nanorod: Polymer solar cells (2002) Science, 295, pp. 2425-2427Sian, S., Chen, C.-W., Polymer-metal-oxide hybrid solar cells (2013) J. Mater. Chem. A, 1, pp. 10574-10591Das, J., A facile nonaqueous route for fabricating titania nanorods and their viability in quasi-solid-state dye-sensitized solar cells (2010) J. Mater. Chem., 20, pp. 4425-4431Cozzoli, P.D., Kornowski, A., Weller, H., Low-temperature synthesis of soluble and processable organic-capped anatase TiO2 nanorods (2003) J. Am. Chem. 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Scaling critical behavior of superconductors at zero magnetic field

We consider the scaling behavior in the critical domain of superconductors at zero external magnetic field. The first part of the paper is concerned with the Ginzburg-Landau model in the zero magnetic field Meissner phase. We discuss the scaling behavior of the superfluid density and we give an alternative proof of Josephson's relation for a charged superfluid. This proof is obtained as a consequence of an exact renormalization group equation for the photon mass. We obtain Josephson's relation directly in the form $\rho_{s}\sim t^{\nu}$, that is, we do not need to assume that the hyperscaling relation holds. Next, we give an interpretation of a recent experiment performed in thin films of $YBa_{2}Cu_{3}O_{7-\delta}$. We argue that the measured mean field like behavior of the penetration depth exponent $\nu'$ is possibly associated with a non-trivial critical behavior and we predict the exponents $\nu=1$ and $\alpha=-1$ for the correlation lenght and specific heat, respectively. In the second part of the paper we discuss the scaling behavior in the continuum dual Ginzburg-Landau model. After reviewing lattice duality in the Ginzburg-Landau model, we discuss the continuum dual version by considering a family of scalings characterized by a parameter $\zeta$ introduced such that $m_{h,0}^2\sim t^{\zeta}$, where $m_{h,0}$ is the bare mass of the magnetic induction field. We discuss the difficulties in identifying the renormalized magnetic induction mass with the photon mass. We show that the only way to have a critical regime with $\nu'=\nu\approx 2/3$ is having $\zeta\approx 4/3$, that is, with $m_{h,0}$ having the scaling behavior of the renormalized photon mass.Comment: RevTex, 15 pages, no figures; the subsection III-C has been removed due to a mistak

Anomalous dimensions and phase transitions in superconductors

The anomalous scaling in the Ginzburg-Landau model for the superconducting phase transition is studied. It is argued that the negative sign of the $\eta$ exponent is a consequence of a special singular behavior in momentum space. The negative sign of $\eta$ comes from the divergence of the critical correlation function at finite distances. This behavior implies the existence of a Lifshitz point in the phase diagram. The anomalous scaling of the vector potential is also discussed. It is shown that the anomalous dimension of the vector potential $\eta_A=4-d$ has important consequences for the critical dynamics in superconductors. The frequency-dependent conductivity is shown to obey the scaling $\sigma(\omega)\sim\xi^{z-2}$. The prediction $z\approx 3.7$ is obtained from existing Monte Carlo data.Comment: RevTex, 20 pages, no figures; small changes; version accepted in PR

Symmetry Nonrestoration in a Gross-Neveu Model with Random Chemical Potential

We study the symmetry behavior of the Gross-Neveu model in three and two dimensions with random chemical potential. This is equivalent to a four-fermion model with charge conjugation symmetry as well as Z_2 chiral symmetry. At high temperature the Z_2 chiral symmetry is always restored. In three dimensions the initially broken charge conjugation symmetry is not restored at high temperature, irrespective of the value of the disorder strength. In two dimensions and at zero temperature the charge conjugation symmetry undergoes a quantum phase transition from a symmetric state (for weak disorder) to a broken state (for strong disorder) as the disorder strength is varied. For any given value of disorder strength, the high-temperature behavior of the charge conjugation symmetry is the same as its zero-temperature behavior. Therefore, in two dimensions and for strong disorder strength the charge conjugation symmetry is not restored at high temperature.Comment: 16 pages, 3 figure

Hamiltonian Study of Improved U(1U(1 Lattice Gauge Theory in Three Dimensions

A comprehensive analysis of the Symanzik improved anisotropic three-dimensional U(1) lattice gauge theory in the Hamiltonian limit is made. Monte Carlo techniques are used to obtain numerical results for the static potential, ratio of the renormalized and bare anisotropies, the string tension, lowest glueball masses and the mass ratio. Evidence that rotational symmetry is established more accurately for the Symanzik improved anisotropic action is presented. The discretization errors in the static potential and the renormalization of the bare anisotropy are found to be only a few percent compared to errors of about 20-25% for the unimproved gauge action. Evidence of scaling in the string tension, antisymmetric mass gap and the mass ratio is observed in the weak coupling region and the behaviour is tested against analytic and numerical results obtained in various other Hamiltonian studies of the theory. We find that more accurate determination of the scaling coefficients of the string tension and the antisymmetric mass gap has been achieved, and the agreement with various other Hamiltonian studies of the theory is excellent. The improved action is found to give faster convergence to the continuum limit. Very clear evidence is obtained that in the continuum limit the glueball ratio $M_{S}/M_{A}$ approaches exactly 2, as expected in a theory of free, massive bosons.Comment: 13 pages, 15 figures, submitted to Phys. Rev.