735 research outputs found
A perturbative approach to J mixing in f-electron systems: Application to actinide dioxides
We present a perturbative model for crystal-field calculations, which keeps
into account the possible mixing of states labelled by different quantum number
J. Analytical J-mixing results are obtained for a Hamiltonian of cubic symmetry
and used to interpret published experimental data for actinide dioxides. A
unified picture for all the considered compounds is proposed by taking into
account the scaling properties of the crystal-field potential.Comment: 16 pages + 4 figures; will appear http://prb.aps.or
Many-body models for molecular nanomagnets
We present a flexible and effective ab-initio scheme to build many-body
models for molecular nanomagnets, and to calculate magnetic exchange couplings
and zero-field splittings. It is based on using localized Foster-Boys orbitals
as one-electron basis. We apply this scheme to three paradigmatic systems, the
antiferromagnetic rings Cr8 and Cr7Ni and the single molecule magnet Fe4. In
all cases we identify the essential magnetic interactions and find excellent
agreement with experiments.Comment: 5 pages, 3 figure
Quantum-gate implementation in permanently coupled AF spin rings without need of local fields
We propose a scheme for the implementation of quantum gates which is based on
the qubit encoding in antiferromagnetic molecular rings. We show that a proper
engineering of the intercluster link would result in an effective coupling that
vanishes as far as the system is kept in the computational space, while it is
turned on by a selective excitation of specific auxiliary states. These are
also shown to allow the performing of single- and two-qubit gates without an
individual addressing of the rings by means of local magnetic fields.Comment: To appear in Physical Review Letter
S-mixing and quantum tunneling of the magnetization in molecular nanomagnets
The role of -mixing in the quantum tunneling of the magnetization in
nanomagnets has been investigated. We show that the effect on the tunneling
frequency is huge and that the discrepancy (more than 3 orders of magnitude in
the tunneling frequency) between spectroscopic and relaxation measurements in
Fe can be resolved if -mixing is taken into account.Comment: REVTEX, 10 pages, 3 jpg figures, to appear in PR
Enhancement of rare-earth--transition-metal exchange interaction in PrFe probed by inelastic neutron scattering
The fundamental magnetic interactions of PrFe are studied by
inelastic neutron scattering and anisotropy field measurements. Data analysis
confirms the presence of three magnetically inequivalent sites, and reveals an
exceptionally large value of the exchange field. The unexpected importance of
-mixing effects in the description of the ground-state properties of
PrFe is evidenced, and possible applications of related compounds
are envisaged.Comment: 4 RevTeX pages, 4 EPS figures. Accepted for publication by Appl.
Phys. Lett. (will be found at http://apl.aip.org
The First Cold Antihydrogen
Antihydrogen, the atomic bound state of an antiproton and a positron, was
produced at low energy for the first time by the ATHENA experiment, marking an
important first step for precision studies of atomic antimatter. This paper
describes the first production and some subsequent developments.Comment: Invitated Talk at COOL03, International Workshop on Beam Cooling and
Related Topics, to be published in NIM
Magnetic Susceptibility of Multiorbital Systems
Effects of orbital degeneracy on magnetic susceptibility in paramagnetic
phases are investigated within a mean-field theory. Under certain crystalline
electric fields, the magnetic moment consists of two independent moments, e.g.,
spin and orbital moments. In such a case, the magnetic susceptibility is given
by the sum of two different Curie-Weiss relations, leading to deviation from
the Curie-Weiss law. Such behavior may be observed in d- and f-electron systems
with t_{2g} and Gamma_8 ground states, respectively. As a potential application
of our theory, we attempt to explain the difference in the temperature
dependence of magnetic susceptibilities of UO_2 and NpO_2.Comment: 4 pages, 3 figure
The Ising-Kondo lattice with transverse field: an f-moment Hamiltonian for URu2Si2?
We study the phase diagram of the Ising-Kondo lattice with transverse
magnetic field as a possible model for the weak-moment heavy-fermion compound
URu2Si2, in terms of two low-lying f singlets in which the uranium moment is
coupled by on-site exchange to the conduction electron spins. In the mean-field
approximation for an extended range of parameters, we show that the conduction
electron magnetization responds logarithmically to f-moment formation, that the
ordered moment in the antiferromagnetic state is anomalously small, and that
the Neel temperature is of the order observed. The model gives a qualitatively
correct temperature-dependence, but not magnitude, of the specific heat. The
majority of the specific heat jump at the Neel temperature arises from the
formation of a spin gap in the conduction electron spectrum. We also discuss
the single-impurity version of the model and speculate on ways to increase the
specific heat coefficient. In the limits of small bandwidth and of small
Ising-Kondo coupling, we find that the model corresponds to anisotropic
Heisenberg and Hubbard models respectively.Comment: 20 pages RevTeX including 5 figures (1 in LaTeX, 4 in uuencoded EPS),
Received by Phys. Rev. B 19 April 199
Molecular engineering of antiferromagnetic rings for quantum computation
The substitution of one metal ion in a Cr-based molecular ring with dominant
antiferromagnetic couplings allows to engineer its level structure and
ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means
of low-temperature specific-heat and torque-magnetometry measurements, thus
determining the microscopic parameters of the corresponding spin Hamiltonian.
The energy spectrum and the suppression of the leakage-inducing S-mixing render
the Cr7Ni molecule a suitable candidate for the qubit implementation, as
further substantiated by our quantum-gate simulations.Comment: To appear in Physical Review Letter
- …