Effective Spin Couplings in the Mott Insulator of the Honeycomb Lattice Hubbard Model

Motivated by the recent discovery of a spin liquid phase for the Hubbard model on the honeycomb lattice at half-filling, we apply both perturbative and non-perturbative techniques to derive effective spin Hamiltonians describing the low-energy physics of the Mott-insulating phase of the system. Exact diagonalizations of the so-derived models on small clusters are performed, in order to assess the quality of the effective low-energy theory in the spin-liquid regime. We show that six-spin interactions on the elementary loop of the honeycomb lattice are the dominant sub-leading effective couplings. A minimal spin model is shown to reproduce most of the energetic properties of the Hubbard model on the honeycomb lattice in its spin-liquid phase. Surprisingly, a more elaborate effective low-energy spin model obtained by a systematic graph expansion rather disagrees beyond a certain point with the numerical results for the Hubbard model at intermediate couplings.Comment: 20 pages, 10 figure

Quantum Critical Scaling of Fidelity Susceptibility

The behavior of the ground-state fidelity susceptibility in the vicinity of a quantum critical point is investigated. We derive scaling relations describing its singular behavior in the quantum critical regime. Unlike it has been found in previous studies, these relations are solely expressed in terms of conventional critical exponents. We also describe in detail a quantum Monte Carlo scheme that allows for the evaluation of the fidelity susceptibility for a large class of many-body systems and apply it in the study of the quantum phase transition for the transverse-field Ising model on the square lattice. Finite size analysis applied to the so obtained numerical results confirm the validity of our scaling relations. Furthermore, we analyze the properties of a closely related quantity, the ground-state energy's second derivative, that can be numerically evaluated in a particularly efficient way. The usefulness of both quantities as alternative indicators of quantum criticality is examined.Comment: 13 pages, 7 figures. Published versio

X, Y and Z States

Many new states in the charmonium mass region were recently discovered by BaBar, Belle, CLEO-c, CDF, D0, BESIII, LHCb and CMS Collaborations. We use the QCD Sum Rule approach to study the possible structure of some of these states.Comment: Contribution for the proceedings of the "XII Quark Confinement and the Hadron Spectrum - CONF12" conferenc

Shotguns vs Lasers: Identifying barriers and facilitators to scaling-up plant molecular farming for high-value health products.

Plant molecular farming (PMF) is a convenient and cost-effective way to produce high-value recombinant proteins that can be used in the production of a range of health products, from pharmaceutical therapeutics to cosmetic products. New plant breeding techniques (NPBTs) provide a means to enhance PMF systems more quickly and with greater precision than ever before. However, the feasibility, regulatory standing and social acceptability of both PMF and NPBTs are in question. This paper explores the perceptions of key stakeholders on two European Union (EU) Horizon 2020 programmes-Pharma-Factory and Newcotiana-towards the barriers and facilitators of PMF and NPBTs in Europe. One-on-one qualitative interviews were undertaken with N = 20 individuals involved in one or both of the two projects at 16 institutions in seven countries (Belgium, France, Germany, Italy, Israel, Spain and the UK). The findings indicate that the current EU regulatory environment and the perception of the public towards biotechnology are seen as the main barriers to scaling-up PMF and NPBTs. Competition from existing systems and the lack of plant-specific regulations likewise present challenges for PMF developing beyond its current niche. However, respondents felt that the communication of the benefits and purpose of NPBT PMF could provide a platform for improving the social acceptance of genetic modification. The importance of the media in this process was highlighted. This article also uses the multi-level perspective to explore the ways in which NPBTs are being legitimated by interested parties and the systemic factors that have shaped and are continuing to shape the development of PMF in Europe

Parameter space of experimental chaotic circuits with high-precision control parameters

ACKNOWLEDGMENTS The authors thank Professor Iberê Luiz Caldas for the suggestions and encouragement. The authors F.F.G.d.S., R.M.R., J.C.S., and H.A.A. acknowledge the Brazilian agency CNPq and state agencies FAPEMIG, FAPESP, and FAPESC, and M.S.B. also acknowledges the EPSRC Grant Ref. No. EP/I032606/1.Peer reviewedPublisher PD

Efeito de retardadores de crescimento na producao de biomassa aerea da cultivar de videira festival.

Com objetivo de observar o efeito dos retardadores de crescimento, Chlormequat e Paclobutrazol 25% aplicados após a poda (AP), sobre a quantidade de biomassa fresca e seca proveniente das plantas de videira ?Festival?, em dois ciclos de produção, realizou-se um experimento em condições de campo em Petrolina-PE