Perturbations on the superconducting state of metallic nanoparticles: influence of geometry and impurities

The pair condensation energy of a finite-size superconducting particle is studied as a function of two control parameters. The first control parameter is the shape of the particle, and the second parameter is a position-dependent impurity introduced in the particle. Whereas the former parameter is known to induce strong fluctuations in the condensation energy, the latter control parameter is found to be a more gentle probe of the pairing correlations.Comment: Submitted for the special issue of the International Symposium on Small Particles and Inorganic Clusters XVI, at KULeuven (July 8-13, 2012). PACS: 74.78.Na, 74.20.F

Exact solution of the px+ipyp_x + ip_y pairing Hamiltonian by deforming the pairing algebra

The present paper makes a connection between collective bosonic states and the exact solutions of the $p_x + ip_y$ pairing Hamiltonian. This makes it possible to investigate the effects of the Pauli principle on the energy spectrum, by gradually reintroducing the Pauli principle. It also introduces an efficient and stable numerical method to probe all the eigenstates of this class of Hamiltonians.Comment: 18 pages, 10 figure

The Dicke model as the contraction limit of a pseudo-deformed Richardson-Gaudin model

The Dicke model is derived in the contraction limit of a pseudo-deformation of the quasispin algebra in the su(2)-based Richardson-Gaudin models. Likewise, the integrability of the Dicke model is established by constructing the full set of conserved charges, the form of the Bethe Ansatz state, and the associated Richardson-Gaudin equations. Thanks to the formulation in terms of the pseudo-deformation, the connection from the su(2)-based Richardson-Gaudin model towards the Dicke model can be performed adiabatically

Eigenvalue-based determinants for scalar products and form factors in Richardson-Gaudin integrable models coupled to a bosonic mode

Starting from integrable $su(2)$ (quasi-)spin Richardson-Gaudin XXZ models we derive several properties of integrable spin models coupled to a bosonic mode. We focus on the Dicke-Jaynes-Cummings-Gaudin models and the two-channel $(p+ip)$-wave pairing Hamiltonian. The pseudo-deformation of the underlying $su(2)$ algebra is here introduced as a way to obtain these models in the contraction limit of different Richardson-Gaudin models. This allows for the construction of the full set of conserved charges, the Bethe Ansatz state, and the resulting Richardson-Gaudin equations. For these models an alternative and simpler set of quadratic equations can be found in terms of the eigenvalues of the conserved charges. Furthermore, the recently proposed eigenvalue-based determinant expressions for the overlaps and form factors of local operators are extended to these models, linking the results previously presented for the Dicke-Jaynes-Cummings-Gaudin models with the general results for Richardson-Gaudin XXZ models

An eigenvalue-based method and determinant representations for general integrable XXZ Richardson-Gaudin models

We propose an extension of the numerical approach for integrable Richardson-Gaudin models based on a new set of eigenvalue-based variables. Starting solely from the Gaudin algebra, the approach is generalized towards the full class of XXZ Richardson-Gaudin models. This allows for a fast and robust numerical determination of the spectral properties of these models, avoiding the singularities usually arising at the so-called singular points. We also provide different determinant expressions for the normalization of the Bethe Ansatz states and form factors of local spin operators, opening up possibilities for the study of larger systems, both integrable and non-integrable. These expressions can be written in terms of the new set of variables and generalize the results previously obtained for rational Richardson-Gaudin models and Dicke-Jaynes-Cummings-Gaudin models. Remarkably, these results are independent of the explicit parametrization of the Gaudin algebra, exposing a universality in the properties of Richardson-Gaudin integrable systems deeply linked to the underlying algebraic structure

Probing pairing correlations in Sn isotopes using Richardson-Gaudin integrability

Pairing correlations in the even-even A=102-130 Sn isotopes are discussed, based on the Richardson-Gaudin variables in an exact Woods-Saxon plus reduced BCS pairing framework. The integrability of the model sheds light on the pairing correlations, in particular on the previously reported sub-shell structure.Comment: Proceedings of the XX International School on Nuclear Physics, Neutron Physics and Applications, Varna, Bulgaria, 16-22 September, 201

Gold nanoparticle-mediated photoporation enables delivery of macromolecules over a wide range of molecular weights in human CD4+ T cells

The modification of CD4+ T cells with exogenous nucleic acids or proteins is a critical step in several research and therapeutic applications, such as HIV studies and cancer immunotherapies. However, efficient cell transfections are not always easily achieved when working with these primary hard-to-transfect cells. While the modification of T cells is typically performed by viral transduction or electroporation, their use is associated with safety issues or cytotoxicity. Vapor nanobubble (VNB) photoporation with sensitizing gold nanoparticles (AuNPs) has recently emerged as a new technology for safe and flexible cell transfections. In this work, we evaluated the potential of VNB photoporation as a novel technique for the intracellular delivery of macromolecules in primary human CD4+ T cells using fluorescent dextrans as model molecules. Our results show that VNB photoporation enables efficient delivery of fluorescent dextrans of 10 kDa in Jurkat (>60% FD10+ cells) as well as in primary human CD4+ T cells (+/- 40% FD10+ cells), with limited cell toxicity (>70% cell viability). We also demonstrated that the technique allows the delivery of dextrans that are up to 500 kDa in Jurkat cells, suggesting its applicability for the delivery of biological macromolecules with a wide range of molecular weights. Altogether, VNB photoporation represents a promising technique for the universal delivery of macromolecules in view of engineering CD4+ T cells for use in a wide variety of research and therapeutic applications

Polynomial scaling approximations and dynamic correlation corrections to doubly occupied configuration interaction wave functions

A class of polynomial scaling methods that approximate Doubly Occupied Configuration Interaction (DOCI) wave functions and improve the description of dynamic correlation is introduced. The accuracy of the resulting wave functions is analysed by comparing energies and studying the overlap between the newly developed methods and full configuration interaction wave functions, showing that a low energy does not necessarily entail a good approximation of the exact wave function. Due to the dependence of DOCI wave functions on the single-particle basis chosen, several orbital optimisation algorithms are introduced. An energy-based algorithm using the simulated annealing method is used as a benchmark. As a computationally more affordable alternative, a seniority number minimising algorithm is developed and compared to the energy based one revealing that the seniority minimising orbital set performs well. Given a well-chosen orbital basis, it is shown that the newly developed DOCI based wave functions are especially suitable for the computationally efficient description of static correlation and to lesser extent dynamic correlation.Fil: Van Raemdonck, Mario. Ghent University; BélgicaFil: Alcoba, Diego Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Poelmans, Ward. Ghent University; BélgicaFil: De Baerdemacker, Stijn. Ghent University; BélgicaFil: Torre, Alicia. Universidad del País Vasco; EspañaFil: Lain, Luis. Universidad del País Vasco; EspañaFil: Massaccesi, Gustavo Ernesto. Universidad de Barcelona. Facultad de Física. Departamento de Física Fomental; EspañaFil: Van Neck, D.. Ghent University; BélgicaFil: Bultinck, P.. Ghent University; Bélgic