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Search Results: 1 - 10 of 462103 matches for " A. Heron "
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Alasdair
Heron
HTS Theological Studies/Teologiese Studies , 2012,
Abstract: The article aims to investigate the Calvin’s Genevan Service Order. It focuses on the question how the Psalter Calvin shaped the worship of the Reformed Church in Geneva. The article follows the critical edition of the Genevan prayer in Calvini Opera Selecta and in the German Studienausgabe as the two main published editions of the Genevan order with its related texts. The article shows that Calvin adhered to the general line of the Swiss and Upper German Reformations. It explores the understanding of worship reflected in the Genevan Service Order and the specific significance of its musical aspect. The article illustrates why Calvin gave the psalms the place he did in Genevan Reformed worship.
Nesting and lifetime effects in the FFLO state of quasi-one-dimensional imbalanced Fermi gases
Heron Caldas,Mucio A. Continentino
Physics , 2013, DOI: 10.1088/0953-4075/46/15/155301
Abstract: Motivated by the recent experimental realization of a candidate to the Fulde-Ferrell (FF) and the Larkin-Ovchinnikov (LO) states in one dimensional (1D) atomic Fermi gases, we study the quantum phase transitions in these enigmatic, finite momentum-paired superfluids. We focus on the FF state and investigate the effects of the induced interaction on the stability of the FFLO phase in homogeneous spin-imbalanced quasi-1D Fermi gases at zero temperature. When this is taken into account we find a direct transition from the fully polarized to the FFLO state. Also, we consider the effect of a finite lifetime of the quasi-particles states in the normal-superfluid instability. In the limit of long lifetimes, the lifetime effect is irrelevant and the transition is directly from the fully polarized to the FFLO state. We show, however, that for sufficiently short lifetimes there is a quantum critical point (QCP), at a finite value of the mismatch of the Fermi wave-vectors of the different quasi-particles, that we fully characterize. In this case the transition is from the FFLO phase to a normal partially polarized state with increasing mismatch.
Quantum normal-to-inhomogeneous superconductor phase transition in nearly two-dimensional metals
Heron Caldas,Mucio A. Continentino
Physics , 2012, DOI: 10.1103/PhysRevB.86.144503
Abstract: In multi-band systems, electrons from different orbitals coexist at the Fermi surface. An attractive interaction among these quasi-particles gives rise to inter-band or hybrid pairs which eventually condense in a superconducting state. These quasi-particles have a natural mismatch of their Fermi wave-vectors, $\delta k_F$, which depends on the strength of the hybridization between their orbitals. The existence of this natural scale suggests the possibility of inhomogeneous superconducting ground states in these systems, even in the absence of an applied magnetic field. Furthermore, since hybridization $V$ depends on pressure, this provides an external parameter to control the wave-vectors mismatch at the Fermi surface. In this work, we study the phase diagram of a two-dimensional, two-band metal with inter-band pairing. We show that as the mismatch between the Fermi wave-vectors of the two hybrid bands is reduced, the system presents a normal-to-inhomogeneous superconductor quantum phase transition at a critical value of the hybridization $V_c=\Delta_0$. The superconducting ground state for $V
Temperature Effects in a Fermi Gas with Population Imbalance
Heron Caldas,A. L. Mota
Statistics , 2008, DOI: 10.1088/1742-5468/2008/08/P08013
Abstract: We investigate temperature effects in a Fermi gas with imbalanced spin populations. From the general expression of the thermal gap equation we find, in {\it weak coupling limit}, an analytical expression for the transition temperature $T_c$ as a function of various possibilities of chemical potential and mass asymmetries between the two particle species. For a range of asymmetry between certain specific values, this equation always has two solutions for $T_c$ which has been interpreted as a reentrant phenomena or a pairing induced by temperature effect. We show that the lower $T_c$ is never related to a stable solution. The same results are obtained in {\it strong coupling limit}. The thermodynamical potential is carefully analyzed to avoid the consideration of the unstable solutions. We also obtain the tricritical points for the chemical potential and mass imbalanced cases, and beyond these points we properly minimize the thermodynamic potential to find the stable and metastable first order transition lines.
Renormalization group approach to a $p$-wave superconducting model
Mucio A. Continentino,Fernanda Deus,Heron Caldas
Physics , 2014, DOI: 10.1016/j.physleta.2014.03.044
Abstract: We present in this work an exact renormalization group (RG) treatment of a one-dimensional $p$-wave superconductor. The model proposed by Kitaev consists of a chain of spinless fermions with a $p$-wave gap. It is a paradigmatic model of great actual interest since it presents a weak pairing superconducting phase that has Majorana fermions at the ends of the chain. Those are predicted to be useful for quantum computation. The RG allows to obtain the phase diagram of the model and to study the quantum phase transition from the weak to the strong pairing phase. It yields the attractors of these phases and the critical exponents of the weak to strong pairing transition. We show that the weak pairing phase of the model is governed by a chaotic attractor being non-trivial from both its topological and RG properties. In the strong pairing phase the RG flow is towards a conventional strong coupling fixed point. Finally, we propose an alternative way for obtaining $p$-wave superconductivity in a one-dimensional system without spin-orbit interaction.
Induced p-wave superconductivity without spin-orbit interactions
Fernanda Deus,Mucio A. Continentino,Heron Caldas
Physics , 2015,
Abstract: The study of Majorana fermions is of great importance for the implementation of a quantum computer. These modes are topologically protected and very stable. It is now well known that a p-wave superconducting wire can sustain, in its topological non-trivial phase, Majorana quasi-particles at its ends. Since this type of superconductor is not found in nature, many methods have been devised to implement it. Most of them rely on the spin-orbit interaction. In this paper we study the superconducting properties of a two-band system in the presence of antisymmetric hybridization. We consider inter-band attractive interactions and also an attractive interaction in one of the bands. We show that superconducting fluctuations with p-wave character are induced in the non-interacting band due to the combined effects of inter-band coupling and hybridization. In the case of a wire, this type of induced superconductivity gives rise to four Majorana modes at its ends. The long range correlation between the different charge states of these modes offers new possibilities for the implementation of protected q-bits.
Mechanism for enhancement of superconductivity in multi-band systems with odd parity hybridization
Mucio A. Continentino,Igor T. Padilha,Heron Caldas
Physics , 2013, DOI: 10.1088/1742-5468/2014/07/P07015
Abstract: The study of multi-band superconductivity is relevant for a variety of systems, from ultra cold atoms with population imbalance to particle physics, and condensed matter. As a consequence, this problem has been widely investigated bringing to light many new and interesting phenomena. In this work we point out and explore a correspondence between a two-band metal with a $k$-dependent hybridization and a uniformly polarized fermionic system in the presence of spin-orbit coupling (SOC). We study the ground state phase diagram of the metal in the presence of an attractive interaction. We find remarkable superconducting properties whenever hybridization mixes orbitals of different parities in neighboring sites. We show that this mechanism enhances superconductivity and drives the crossover from weak to strong coupling in analogy with SOC in cold atoms. We obtain the quantum phase transitions between the normal and superfluid states, as the intensity of different parameters characterizing the metal are varied, including Lifshitz transitions, with no symmetry breaking, associated with the appearance of soft modes in the Fermi surface.
Topological states in normal and superconducting $p$-wave chains
Mucio A. Continentino,Heron Caldas,David Nozadze,Nandini Trivedi
Physics , 2014, DOI: 10.1016/j.physleta.2014.09.022
Abstract: We study a two-band model of fermions in a 1d chain with an antisymmetric hybridization that breaks inversion symmetry. We find that for certain values of its parameters, the $sp$-chain maps formally into a $p$-wave superconducting chain, the archetypical 1d system exhibiting Majorana fermions. The eigenspectra, including the existence of zero energy modes in the topological phase, agree for both models. The end states too share several similarities in both models, such as the behavior of the localization length, the non-trivial topological index and robustness to disorder. However, we show by mapping the $s$- and $p$- fermions to two copies of Majoranas, that the excitations in the ends of a finite $sp$ chain are indeed conventional fermions though endowed with protected topological properties. Our results are obtained by a scattering approach in a semi-infinite chain with an edge defect treated within the $T$-matrix approximation. We augment the analytical results with exact numerical diagonalization that allow us to extend our results to arbitrary parameters and also to disordered systems.
Phase Transition in Asymmetrical Superfluids I: Equal Fermi Surfaces
Heron Caldas,C. W. Morais,A. L. Mota
Physics , 2005, DOI: 10.1103/PhysRevD.72.045008
Abstract: In this paper, we study phase transitions in asymmetrical fermion superfluids. In this scenario, the candidates to form pair are particles with mismatched masses and chemical potentials. We derive an expression for the critical temperature in terms of the gap and masses (or chemical potentials) when the constraint of equal Fermi surfaces $m_a\mu_a = m_b\mu_b$ is imposed.
“If Luther will accept us with our confession …”: The Eucharistic controversy in Calvin’s correspondence up to 1546
Alasdair Heron
HTS Theological Studies/Teologiese Studies , 2009, DOI: 10.4102/hts.v62i3.390
Abstract: The article explores Calvin's attitude to the Eucharistic controversy between Wittenberg and Zurich in the years up till Luther's death in 1546. The main source is Calvin’s letters from that period, which cast a differentiated light on his aims, hopes and disappointments on the question as well as on his relations to other leading Reformers. Account is also taken of several recent publications, which suggest revision of some long-standing views in Calvin scholarship.
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