Explicit Local Integrals of Motion for the Many-Body Localized State

Recently, it has been suggested that the Many-Body Localized phase can be characterized by local integrals of motion. Here we introduce a Hilbert space preserving renormalization scheme that iteratively finds such integrals of motion exactly. Our method is based on the consecutive action of a similarity transformation using displacement operators. We show, as a proof of principle, localization and the delocalization transition in interacting fermion chains with random onsite potentials. Our scheme of consecutive displacement transformations can be used to study Many Body Localization in any dimension, as well as disorder-free Hamiltonians.Comment: 5 pages, 2 figures, and Supplementary Information. Second version contains new numerical result

Quantum Thermalization and the Expansion of Atomic Clouds

The ultimate consequence of quantum many-body physics is that even the air we breathe is governed by strictly unitary time evolution. The reason that we perceive it nonetheless as a completely classical high temperature gas is due to the incapacity of our measurement machines to keep track of the dense many-body entanglement of the gas molecules. The question thus arises whether there are instances where the quantum time evolution of a macroscopic system is qualitatively different from the equivalent classical system? Here we study this question through the expansion of noninteracting atomic clouds. While in many cases the full quantum dynamics is indeed indistinguishable from classical ballistic motion, we do find a notable exception. The subtle quantum correlations in a Bose gas approaching the condensation temperature appear to affect the expansion of the cloud, as if the system has turned into a diffusive collision-full classical system.Comment: 6 pages, 4 figures, and a 4-page supplementary informatio

Charge-transfer insulation in twisted bilayer graphene

We studied the real space structure of states in twisted bilayer graphene at the `magic angle' $\theta = 1.08^\circ$. The flat bands close to charge neutrality are composed of a mix of `ring' and `center' orbitals around the AA stacking region. An effective model with localized orbitals is constructed, which necessarily includes more than just the four flat bands. Long-range Coulomb interaction causes a charge-transfer at half-filling of the flat bands from the `center' to the `ring' orbitals. Consequently, the Mott phase is a featureless spin-singlet paramagnet. We estimate the effective Heisenberg coupling that favors the singlet coupling to be $J = 3.3$ K, consistent with experimental values. The superconducting state depends on the nature of the dopants: hole-doping yields $p+ip$-wave whereas electron-doping yields $d+id$-wave pairing symmetry.Comment: 8 pages, 6 figures. This second version contains more detailed computations on the Coulomb energy from the unequal charge distributio

Advertising Media and the Green Environmental Aspect

Previous research has shown that consumer trust in advertising is low and continues to diminish. Researchers have also found that a big share of advertising investments is placed in less favorable media which can contribute to consumers’ increasing disbelief towards advertising. The results of the present study add to these previous findings by showing that the consumers’ trust levels in advertising vary among the 11 different media studied and that the marketing managers’ beliefs about consumers are not consistent with the consumers’ attitudes toward and usage of advertising media. Ignoring this phenomenon may have consequences for companies investing in less favorable media and thereby adding to consumers’ increasing disbelief towards advertising. The greatest discrepancy was found for ads on TV. The marketing managers seem to believe incorrectly that ads on TV are not only more trusted but also more used by consumers than the consumers claim. The consumers were found to have more negative attitudes toward TV advertising than what the marketing managers believe about consumers. TV is also perceived by the consumers as more harmful for the green environment than the marketing managers believe about consumers. The results show that the consumers have more positive attitudes toward direct marketing than the marketing managers believe about them. The consumers perceive direct marketing as better, less irritating and less harmful for the environment compared to the marketing managers’ beliefs about them. In addition, the consumers claim to make more use of ads in many of the paper-based media than TV advertising when they want to buy different products. This was found to be not consistent with the marketing managers’ beliefs about consumers. The consumers were found to have more negative attitudes toward advertising through the mobile phone than the marketing managers believe about consumers. Advertising through the mobile phone is considered by the consumers as one of the worst, most irritating and least trusted medium among the 11 advertising media studied. Moreover, the consumers consider the mobile phone to be more harmful for the green environment compared to the marketing managers’ beliefs about consumers. The results also show that the marketing managers feel more personal responsible towards caring for the green environment than the consumers. In addition, both the marketing managers and the consumers were found to have equally high demands and expectations of organizations to act responsibly toward the green environment. This contradicts previous findings that showed that the green environmental aspect is among the factors that are the least considered when marketing managers work with marketing communication in general and advertising media selection in particular. Furthermore, this study found that green environmental responsibility attitude (GERA) is weakly related to the perception on the green environmental aspect of advertising media. Thus, the discrepancies found in this study between the consumers and marketing managers regarding their green environmental perceptions on the 11 different advertising media should be explained by other factors.Advertising Media; Attitudes; Consumers; Marketing Managers; Green Environment; Green Environmental Responsibility Attitude (GERA);

A threshold for majority in the context of aggregating partial order relations

We consider a voting problem where voters have expressed their preferences on a single set of objects. These preferences take the shape of strict partial order relations. In order to allow extraction of a unique strict partial order relation corresponding to a social set of preferences, we determine the minimum number of votes a pairwise preference should receive in order to qualify as a social pairwise preference. Transitive closure of the social pairwise preferences will result in the social set of preferences. At the same time, the social set of preferences needs to be cycle-free, and the minimum number of votes should be determined with this constraint in mind. We provide an example application

Construction of Many-Body Eigenstates with Displacement Transformations

Many-body eigenstates beyond the gaussian approximation can be constructed in terms of local integrals of motion (IOM), although their actual computation has been until now a daunting task. We present a new practical computation of IOMS based on displacement transformations. It represents a general and systematic way to extend Hartree-Fock and configuration interaction theories to higher order. Our method combines minimization of energy and energy variance of a reference state with exact diagonalization. We show that our implementation is able to perform ground state calculations with high precision for relatively large systems. Since it keeps track of the IMO's forming a reference state, our method is particularly efficient dealing with excited states, both in accuracy and the number of different states that can be constructed

Avoiding Stripe Order: Emergence of the Supercooled Electron Liquid

In the absence of disorder, electrons can display glassy behavior through supercooling the liquid state, avoiding the solidification into a charge ordered state. Such supercooled electron liquids are experimentally found in organic $\theta$-$MM'$ compounds. We present theoretical results that qualitatively capture the experimental findings. At intermediate temperatures, the conducting state crosses over into a weakly insulating pseudogap phase. The stripe order phase transition is first order, so that the liquid phase is metastable below $T_s$. In the supercooled liquid phase the resistivity increases further and the density of states at the Fermi level is suppressed, indicating kinetic arrest and the formation of a glassy state. Our results are obtained using classical Extended Dynamical Mean Field Theory.Comment: 4 pages, 4 figures, submitted to the proceedings of "Superstripes 2015", Journal of Superconductivity and Novel Magnetism (2015

Suppressed Density of States in Self-Generated Coulomb Glasses

We investigate the structure of metastable states in self-generated Coulomb glasses. In dramatic contrast to disordered electron glasses, we find that these states lack marginal stability. Such absence of marginal stability is reflected by the suppression of the single-particle density of states into an exponentially soft gap of the form $g(\epsilon) \sim e^{-V / \xi |\epsilon|}$. To analytically explain this behavior, we extend the stability criterion of Efros and Shklovskii to incorporate local charge correlations, in qualitative agreement with our numerical findings. Our work suggests the existence of a new class of self-generated glasses dominated by strong geometric frustration.Comment: v3 is the published version in New Journal of Physic

Enhanced superconductivity due to forward scattering in FeSe thin films on SrTiO3 substrates

We study the consequences of an electron-phonon ($e$-$ph$) interaction that is strongly peaked in the forward scattering ($\mathbf{q} = 0$) direction in a two-dimensional superconductor using Migdal-Eliashberg theory. We find that strong forward scattering results in an enhanced $T_c$ that is linearly proportional to the strength of the dimensionless $e$-$ph$ coupling constant $\lambda_m$ in the weak coupling limit. This interaction also produces distinct replica bands in the single-particle spectral function, similar to those observed in recent angle-resolved photoemission experiments on FeSe monolayers on SrTiO$_3$ and BaTiO$_3$ substrates. By comparing our model to photoemission experiments, we infer an $e$-$ph$ coupling strength that can provide a significant portion of the observed high $T_c$ in these systems.Comment: Main text 5 pages, 4 figures; and Supplementary Informatio