531 research outputs found
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
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
Low-temperature antihydrogen-atom scattering
A simple method to include the strong force in atom-antiatom scattering is
presented. It is based on the strong-force scatteringn length between the
nucleon and antinucleon. Using this method elastic and annihilation cross
sections are calculated for hydrogen-antihydrogen and helium-antihydrogen
scattering. The results are compared to first-order perturbation theory using a
pseudo potential. The pseudo-potential approach works fairly well for
hydrogen-antihydrogen scattering, but fails for helium-antihydrogen scattering
where strong-force effects are more prominent.Comment: 9 pages, 2 figures, to be published in Nuclear Instruments and
Methods
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
Molecular nanomagnets as quantum simulators
Quantum simulators are controllable systems that can be used to simulate
other quantum systems. Here we focus on the dynamics of a chain of molecular
qubits with interposed antiferromagnetic dimers. We theoretically show that its
dynamics can be controlled by means of uniform magnetic pulses and used to
mimic the evolution of other quantum systems, including fermionic ones. We
propose two proof-of-principle experiments, based on the simulation of the
Ising model in transverse field and of the quantum tunneling of the
magnetization in a spin-1 system.Comment: Phys. Rev. Lett., in pres
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