1,319 research outputs found
Phase structure of the two-fluid proton-neutron system
The phase structure of a two-fluid bosonic system is investigated. The
proton-neutron interacting boson model (IBM-2) posesses a rich phase structure
involving three control parameters and multiple order parameters. The surfaces
of quantum phase transition between spherical, axially-symmetric deformed, and
SU*(3) triaxial phases are determined.Comment: RevTeX 4, 4 pages, as published in Phys. Rev. Let
X(5) Critical-Point Structure in a Finite System
X(5) is a paradigm for the structure at the critical point of a particular
first-order phase transition for which the intrinsic energy surface has two
degenerate minima separated by a low barrier. For a finite system, we show that
the dynamics at such a critical point can be described by an effective
deformation determined by minimizing the energy surface after projection onto
angular momentum zero, and combined with two-level mixing. Wave functions of a
particular analytic form are used to derive estimates for energies and
quadrupole rates at the critical point.Comment: 14 pages, 1 figure, 2 tables, Phys. Rev. C in pres
Quantum Shape-Phase Transitions in Finite Nuclei
Quantum shape-phase transitions in finite nuclei are considered in the
framework of the interacting boson model. Critical-point Hamiltonians for
first- and second-order transitions are identified by resolving them into
intrinsic and collective parts. Suitable wave functions and finite-N estimates
for observables at the critical-points are derived.Comment: 6 pages, 2 figures, Proc. 2nd Int. Conf. on "Collective Motion in
Nuclei under Extreme Conditions" (COMEX 2), June 20-23, 2006, Sankt Goar,
German
Analytic descriptions for transitional nuclei near the critical point
Exact solutions of the Bohr Hamiltonian with a five-dimensional square well
potential, in isolation or coupled to a fermion by the five-dimensional
spin-orbit interaction, are considered as examples of a new class of dynamical
symmetry or Bose-Fermi dynamical symmetry. The solutions provide baselines for
experimental studies of even-even [E(5)] and odd-mass [E(5|4)] nuclei near the
critical point of the spherical to deformed gamma-unstable phase transition.Comment: LaTeX (elsart), 53 pages; typographical correction to (3.15
Quantum phase transitions in Bose-Fermi systems
Quantum phase transitions in a system of N bosons with angular momentum L=0,2
(s,d) and a single fermion with angular momentum j are investigated both
classically and quantum mechanically. It is shown that the presence of the odd
fermion strongly influences the location and nature of the phase transition,
especially the critical value of the control parameter at which the phase
transition occurs. Experimental evidence for the U(5)-SU(3) (spherical to
axially-deformed) transition in odd-even nuclei is presented.Comment: 38 pages, 29 figure
Algebraic approach to vibrational spectra of tetrahedral molecules: a case study of silicon tetrafluoride
Both the stretch and bend vibrational spectrum and the intensity of infrared
transitions in a tetrahedral molecule are studied in a U(2) algebraic model,
where the spurious states in the model Hamiltonian and the wavefunctions are
exactly removed. As an example, we apply the model to silicon tetrafluoride
SiF.Comment: Revtex, 7 pages, no figure, to appear in Chem. Phys. Let
Quantum Phase Transitions in the U(5)-O(6) Large N limit
The U(5)-O(6) transitional behavior of the Interacting Boson Model in the
large N limit is revisited. Some low-lying energy levels, overlaps of the
ground state wavefunctions, B(E2) transition rate for the decay of the first
excited energy level to the ground state, and the order parameters are
calculated for different total numbers of bosons. The results show that
critical behaviors of these quantities are greatly enhanced with increasing of
the total number of bosons N, especially fractional occupation probability for
d bosons in the ground state, the difference between the expectation value of
n_d in the first excited 0^+ state and the ground state, and another quantity
related to the isomer shift behave similarly in both the O(6)-U(5) large N and
U(5)-SU(3) phase transitions.Comment: 7 Pages LaTeX, 3 figure
Coulomb analogy for nonhermitian degeneracies near quantum phase transitions
Degeneracies near the real axis in a complex-extended parameter space of a
hermitian Hamiltonian are studied. We present a method to measure distributions
of such degeneracies on the Riemann sheet of a selected level and apply it in
classification of quantum phase transitions. The degeneracies are shown to
behave similarly as complex zeros of a partition function.Comment: 4 page
Critical point symmetries in boson-fermion systems. The case of shape transition in odd nuclei in a multi-orbit model
We investigate phase transitions in boson-fermion systems. We propose an
analytically solvable model (E(5/12)) to describe odd nuclei at the critical
point in the transition from the spherical to -unstable behaviour. In
the model, a boson core described within the Bohr Hamiltonian interacts with an
unpaired particle assumed to be moving in the three single particle orbitals
j=1/2,3/2,5/2. Energy spectra and electromagnetic transitions at the critical
point compare well with the results obtained within the Interacting Boson
Fermion Model, with a boson-fermion Hamiltonian that describes the same
physical situation.Comment: Phys. Rev. Lett. (in press
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