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Search Results: 1 - 10 of 401275 matches for " M. Barbier "
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On the Use of Quantum Algebras in Rotation-Vibration Spectroscopy
R. Barbier,M. Kibler
Physics , 1995,
Abstract: A two-parameter deformation of the Lie algebra u$_2$ is used, in conjunction with the rotor system and the oscillator system, to generate a model for rotation-vibration spectroscopy of molecules and nuclei.
Application of a Two-Parameter Quantum Algebra to Rotational Spectroscopy of Nuclei
R. Barbier,M. Kibler
Physics , 1996, DOI: 10.1016/0034-4877(96)88953-1
Abstract: A two-parameter quantum algebra $U_{qp}({\rm u}_2)$ is briefly investigated in this paper. The basic ingredients of a model based on the $U_{qp}({\rm u}_2)$ symmetry, the $qp$-rotator model, are presented in detail. Some general tendencies arising from the application of this model to the description of rotational bands of various atomic nuclei are summarized.
A System of Interest in Spectroscopy: The qp-Rotor System
R. Barbier,M. Kibler
Physics , 1999,
Abstract: A rotor system, having the symmetry afforded by the two-parameter quantum algebra Uqp(u(2)), is investigated in this communication. This system is useful in rotational spectroscopy of molecules and nuclei. In particular, it is shown to lead to a model (viz., the qp-rotor model) for describing (via an energy formula and a qp-deformation of E2 reduced transition probabilities) rotational bands of deformed and superdeformed nuclei.
Dirac electrons in a Kronig-Penney potential: dispersion relation and transmission periodic in the strength of the barriers
M. Barbier,P. Vasilopoulos,F. M. Peeters
Physics , 2009, DOI: 10.1103/PhysRevB.80.205415
Abstract: The transmission T and conductance G through one or multiple one-dimensional, delta-function barriers of two-dimensional fermions with a linear energy spectrum are studied. T and G are periodic functions of the strength P of the delta-function barrier V(x,y) / hbar v_F = P delta(x). The dispersion relation of a Kronig-Penney (KP) model of a superlattice is also a periodic function of P and causes collimation of an incident electron beam for P = 2 pi n and n integer. For a KP superlattice with alternating sign of the height of the barriers the Dirac point becomes a Dirac line for P = (n + 1/2) pi.
Extra Dirac points in the energy spectrum for superlattices on single-layer graphene
M. Barbier,P. Vasilopoulos,F. M. Peeters
Physics , 2010, DOI: 10.1103/PhysRevB.81.075438
Abstract: We investigate the emergence of extra Dirac points in the electronic structure of a periodically spaced barrier system, i.e., a superlattice, on single-layer graphene, using a Dirac-type Hamiltonian. Using square barriers allows us to find analytic expressions for the occurrence and location of these new Dirac points in k-space and for the renormalization of the electron velocity near them in the low-energy range. In the general case of unequal barrier and well widths the new Dirac points move away from the Fermi level and for given heights of the potential barriers there is a minimum and maximum barrier width outside of which the new Dirac points disappear. The effect of these extra Dirac points on the density of states and on the conductivity is investigated.
Kronig-Penney model on bilayer graphene: spectrum and transmission periodic in the strength of the barriers
M. Barbier,P. Vasilopoulos,F. M. Peeters
Physics , 2011, DOI: 10.1103/PhysRevB.82.235408
Abstract: We show that the transmission through single and double {\delta}-function potential barriers of strength P in bilayer graphene is periodic in P with period {\pi}. For a certain range of P values we find states that are bound to the potential barrier and that run along the potential barrier. Similar periodic behaviour is found for the conductance. The spectrum of a periodic succession of {\delta}-function barriers (Kronig-Penney model) in bilayer graphene is periodic in P with period 2{\pi}. For P smaller than a critical value, the spectrum exhibits two Dirac points while for P larger than this value an energy gap opens. These results are extended to the case of a superlattice of {\delta}-function barriers with P alternating in sign between successive barriers; the corresponding spectrum is periodic in P with period {\pi}.
Single-layer and bilayer graphene superlattices: collimation, additional Dirac points and Dirac lines
M. Barbier,P. Vasilopoulos,F. M. Peeters
Physics , 2011, DOI: 10.1098/rsta.2010.0218
Abstract: We review the energy spectrum and transport properties of several types of one- dimensional superlattices (SLs) on single-layer and bilayer graphene. In single-layer graphene, for certain SL parameters an electron beam incident on a SL is highly collimated. On the other hand there are extra Dirac points generated for other SL parameters. Using rectangular barriers allows us to find analytic expressions for the location of new Dirac points in the spectrum and for the renormalization of the electron velocities. The influence of these extra Dirac points on the conductivity is investigated. In the limit of {\delta}-function barriers, the transmission T through, conductance G of a finite number of barriers as well as the energy spectra of SLs are periodic functions of the dimensionless strength P of the barriers, P{\delta}(x) ~ V (x). For a Kronig-Penney SL with alternating sign of the height of the barriers the Dirac point becomes a Dirac line for P = {\pi}/2 + n{\pi} with n an integer. In bilayer graphene, with an appropriate bias applied to the barriers and wells, we show that several new types of SLs are produced and two of them are similar to type I and type II semiconductor SLs. Similar as in single-layer graphene extra "Dirac" points are found. Non-ballistic transport is also considered.
An $U_{qp}(u_2)$ Rotor Model for Rotational Bands of Superdeformed Nuclei
R. Barbier,J. Meyer,M. Kibler
Physics , 1995, DOI: 10.1142/S0218301395000122
Abstract: A nonrigid rotor model is developed from the two-parameter quantum algebra $U_{qp}({\rm u}_2)$. [This model presents the $U_{qp}({\rm u}_2)$ symmetry and shall be referred to as the qp-rotor model.] A rotational energy formula as well as a qp-deformation of E2 reduced transition probabilities are derived. The qp-rotor model is applied (through fitting procedures) to twenty rotational bands of superdeformed nuclei in the $A \sim 130$, 150 and 190 mass regions. Systematic comparisons between the qp-rotor model and the q-rotor model of Raychev, Roussev and Smirnov, on one hand, and a basic three-parameter model, on the other hand, are performed on energy spectra, on dynamical moments of inertia and on B(E2) values. The physical signification of the deformation parameters q and p is discussed.
An Uqp(u2) Model for Rotational Bands of Nuclei
R. Barbier,J. Meyer,M. Kibler
Physics , 1994, DOI: 10.1088/0954-3899/20/1/003
Abstract: A rotational model is developed from a new version of the two-parameter quantum algebra $U_{qp}({\rm u}_2)$. This model is applied to the description of some recent experimental data for the rotating superdeformed nuclei $^{192-194-196-198}{\rm Pb}$ and $^{192-194 }{\rm Hg}$. A comparison between the $U_{qp}({\rm u}_2)$ model presented here and the Raychev-Roussev-Smirnov model with $U_{q }({\rm su}_2)$ symmetry shows the relevance of the introduction of a second parameter of a ``quantum algebra'' type.
Spontaneous four-wave mixing in liquid-core fibers: Towards fibered Raman-free correlated photon sources
M. Barbier,I. Zaquine,P. Delaye
Physics , 2015, DOI: 10.1088/1367-2630/17/5/053031
Abstract: We experimentally demonstrate, for the first time to our knowledge, the generation of correlated photon pairs in a liquid-core photonic crystal fiber. Moreover, we show that, thanks to the specific Raman properties of liquids, the Raman noise (which is the main limitation of the performance of silica-core fiber-based correlated photon pair sources) is highly reduced. With a demonstrated coincident-to-accidental ratio equal to 63 and a pair generation efficiency of about 10$^{-4}$ per pump pulse, this work opens the way for the development of high quality correlated photon pair sources for quantum communications.
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