Family of chiral two- plus three-nucleon interactions for accurate nuclear structure studies
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Hüther, Thomas (ORCID:000000031503613X)↗
Engineering topics
Roth, Robert
Publications and source records attributed to Roth, Robert.
Nuclear Charge Radii of B 10 , 11
The first laser spectroscopic determination of the change in the nuclear charge radius for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-accuracy measurement of the isotope shift in the 2s 2 2p 2 P 1/2 → 2s 2 3s 2 S 1/2 ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes 10,11 B and the results are used to extract their difference in the mean-square charge radius < r$^{2}_{c}$ > 11– < r$^{2}_{c}$ >10= –0.49(12) fm 2 . The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used to benchmark new ab initio nuclear structure calculations using the no-core shell model and Green’s function Monte Carlo approaches. These results are the foundation for a laser spectroscopic determination of the charge radius of the proton-halo candidate 8 B.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Designing Morphotropic Phase Composition in BiFeO 3
In classical morphotropic piezoelectric materials, rhombohedral and tetragonal phase variants can energetically compete to form a mixed phase regime with improved functional properties. Even though the discovery of morphotropic-like phases in multiferroic BiFeO 3 films has broadened this definition, accessing these phase spaces is still typically accomplished through isovalent substitution or heteroepitaxial strain which do not allow for continuous modification of phase composition postsynthesis. In this work, we show that it is possible to use low-energy helium implantation to tailor morphotropic phases of epitaxial BiFeO 3 films postsynthesis in a continuous and iterative manner. Applying this strain doping approach to morphotropic films creates a new phase space based on internal and external lattice stress that can be seen as an analogue to temperature–composition phase diagrams of classical morphotropic ferroelectric systems.
36 MATERIALS SCIENCE↗
Hypernuclear no-core shell model
We extend the No-Core Shell Model (NCSM) methodology to incorporate strangeness degrees of freedom and apply it to single-Λ hypernuclei. After discussing the transformation of the hyperon-nucleon (YN) interaction into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group transformation applied to it to improve model-space convergence, we introduce two complementary formulations of the NCSM, one that uses relative Jacobi coordinates and symmetry-adapted basis states to fully exploit the symmetries of the hypernuclear Hamiltonian, and one working in a Slater determinant basis of HO states where antisymmetrization and computation of matrix elements is simple and to which an importance-truncation scheme can be applied. For the Jacobi-coordinate formulation, we give an iterative procedure for the construction of the antisymmetric basis for arbitrary particle number and present the formulae used to embed two- and three-baryon interactions into the many-body space. For the Slater-determinant formulation, we report on the conversion of the YN interaction matrix elements from relative to single-particle coordinates, the importance-truncation scheme that tailors the model space to the description of the low-lying spectrum, and the role of the redundant center-of-mass degrees of freedom. We end with a confirmation of both formulations in the four-body system, giving converged ground-state energies for a chiral Hamiltonian, and present a short survey of the A ≤ 7 hyper-helium isotopes.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Field-Polarity-Dependent Domain Growth in Epitaxial BaTiO 3 Films
The growth of circular tip-induced domains has been studied in epitaxial BaTiO 3 (BTO) films as a function of writing voltage and time using piezoresponse force microscopy (PFM). While abundant for Pb(Zr,Ti)O 3 (PZT) films, such studies are rare for BTO. Strong relaxation of written domains is observed in the form of reduction of the PFM amplitude inside the area of written domains which occurs additionally to a decrease of the domain radius. The domain wall velocity observed for negative tip voltage is systematically smaller than that for positive tip voltage. Based on maps of the positive and negative switching fields, the effective driving field for both polarities has been estimated. The polarity-dependent effective field cannot account for the different velocities, indicating a polarity-dependent mobility of the domain walls.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗