Using the density matrix renormalization group algorithm, we investigate the lattice model for spinless fermions in one dimension in the presence of a strong interaction and disorder. The phase sensitivity of the ground state energy is determined with high accuracy for systems up to a size of 60 lattice constants. This quantity is found to be log-normally distributed. The fluctuations grow algebraically with system size with a universal exponent of ≈ 2/3 in the localized region of the phase diagram. Surprisingly, we find, for an attractive interaction, a delocalized phase of finite extension. The boundary of this delocalized phase is determined.PACS numbers: 71.30.+h, 72.15.RnThe influence of electron-electron interaction on Anderson localization has attracted a lot of interest for several years. Many recent studies were motivated by the experimental observation of persistent currents in mesoscopic rings [1]. Motivated by an early suggestion [2] that the interaction between the electrons may give a significant contribution to the average persistent current, this phenomenon in the presence of both interaction and disorder has been investigated by various methods [3][4][5][6][7][8]. Nevertheless, the magnitude of the effect is still not well understood.In one dimension, interacting systems in the absence of disorder [9][10][11], as well as for disordered systems in the absence of interactions [12] are well studied. However, a clear understanding of the interplay between interaction and disorder has not yet been obtained. In this Letter, we present novel results of a detailed study of a simple interacting-fermion model with disorder. We determine the ground state phase sensitivity with high accuracy for a wide range of parameters and system sizes up to 60 lattice constants. Our main results are (i) a universal behavior of the rms-value of the logarithmic phase sensitivity, which grows with system size, M , proportional to M 2/3 in the localized region, and (ii) the zero-temperature phase diagram, which shows, for an attractive interaction a delocalized phase of finite extension.The numerical results are obtained with the density matrix renormalization group algorithm (DMRG) [13], which allows calculation of ground state properties of disordered, interacting fermion systems with an accuracy which is comparable to exact diagonalization, but for much larger systems [14,15]. In our implementation of the DMRG we perform 5 finite lattice sweeps keeping up to 750 states per block.We consider a chain of spinless fermions with nearestneighbor interaction and disorder,and twisted boundary conditions, c 0 = e iφ c M . The length of the chain is denoted by M , and the particle number is N . For simplicity, we will set t = 1 in some of the formulas below.The ground state energy E(φ) depends on the phase φ. The energy difference between periodic and anti-periodic boundary conditions, ∆E = (−), and the charge stiffness, D ∼ E ′′ (φ = 0), are a measure of the phase sensitivity of the system. In the clean limit, i.e. ǫ n = 0 for al...

Performing an analysis within density functional theory, we develop insight into the structural and electronic properties of the oxide heterostructure LaAlO 3 /SrTiO 3 . Electrostatic surface effects are decomposed from the internal lattice distortion in order to clarify their interplay. We first study the interface relaxation by a multi-layer system without surface, and the surface effects, separately, by a substrate-film system. While elongation of the TiO 6 octahedra at the interface enhances the metallicity, reduction of the film thickness has the opposite effect due to a growing charge depletion.The interplay of these two effects, as reflected by the full lattice relaxation in the substrate-film system, however, strongly depends on the film thickness. An inversion of the TiO 6 distortion pattern for films thinner than four LaAlO 3 layers results in an insulating state.

We study the influence of many-particle interaction in a system which, in the single particle case, exhibits a metal-insulator transition induced by a finite amount of onsite pontential fluctuations. Thereby, we consider the problem of interacting particles in the one-dimensional quasiperiodic Aubry-André chain. We employ the density-matrix renormalization scheme to investigate the finite particle density situation. In the case of incommensurate densities, the expected transition from the single-particle analysis is reproduced. Generally speaking, interaction does not alter the incommensurate transition. For commensurate densities, we map out the entire phase diagram and find that the transition into a metallic state occurs for attractive interactions and infinite small fluctuations -in contrast to the case of incommensurate densities. Our results for commensurate densities also show agreement with a recent analytic renormalization group approach. 71.30.+h,71.27.+a

We report on surface effects on the electronic properties of interfaces in epitaxial LaAlO 3 /SrTiO 3 heterostructures. Our results are based on first-principles electronic structure calculations for wellrelaxed multilayer configurations, terminated by an ultrathin LaAlO 3 surface layer. On varying the thickness of this layer, we find that the interface conduction states are subject to almost rigid band shifts due to a modified Fermi energy. Confirming experimental data, the electronic properties of heterointerfaces therefore can be tuned systematically by alterating the surface-interface distance.We expect that this mechanism is very general and applies to most oxide heterostructures.

The magnetic and electronic properties of metal phthalocyanines (MPc) and fluorinated metal phthalocyanines (F 16 MPc) are studied by means of spin density functional theory (SDFT). Several metals (M) such as Ca, all first d-row transition metals and Ag are investigated. By considering different open shell transition metals it is possible to tune the electronic properties of MPc, in particular the electronic molecular gap and total magnetic moment. Besides assigning the structural and electronic properties of MPc and F 16 MPc, the vibrational modes analysis of the ScPc-ZnPc series have been studied and correlated to experimental measurements when available.