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Preferential weakening of rotational magnetic anisotropy by keV-He ion bombardment in polycrystalline exchange bias layer systems
(2018-05-04)
The consequences of keV light-ion bombardment of polycrystalline exchange bias layer systems on individual magnetic anisotropies composing the effective unidirectional magnetic anisotropy are investigated by vectorial magneto-optic Kerr effect measurements. Preferential reduction of rotatable magnetic anisotropy as compared to the other magnetic anisotropies is observable, disproving the intuitive assumption of an equable weakening of all magnetic anisotropies due to the bombardment. It is concluded that light-ion ...
Aufsatz
Exploiting non-Markovianity for quantum control
(Nature Publishing Group, 2015)
Quantum technology, exploiting entanglement and the wave nature of matter, relies on the ability to accurately control quantum systems. Quantum control is often compromised by the interaction of the system with its environment since this causes loss of amplitude and phase. However, when the dynamics of the open quantum system is non-Markovian, amplitude and phase flow not only from the system into the environment but also back. Interaction with the environment is then not necessarily detrimental. We show that the ...
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Vesicle motion during sustained exocytosis in chromaffin cells
(PLoS, 2015)
Chromaffin cells release catecholamines by exocytosis, a process that includes vesicle docking, priming and fusion. Although all these steps have been intensively studied, some aspects of their mechanisms, particularly those regarding vesicle transport to the active sites situated at the membrane, are still unclear. In this work, we show that it is possible to extract information on vesicle motion in Chromaffin cells from the combination of Langevin simulations and amperometric measurements. We developed a numerical ...
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Femtosecond probing of sodium cluster ion Na_n ^+ fragmentation
(1992)
We report on the first femtosecond time-resolved experiments in cluster physics. The photofragmentation
dynamics of small sodium cluster ions Na_n ^+ have been studied with pump-probe techniques. Ultrashort
laser pulses of 60-fs duration are employed to photoionize the sodium clusters and to probe the
photofragments. We find that the ejection of neutral dimer Na_2 and, observed for the first time, neutral
trimer Na_3 photofragments occur on ultrashort time scales of 2.5 and 0.4 ps, respectively. This and the
absence ...
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Femtosecond time-resolved molecular multiphoton ionization: the Na_2 system
(1991)
We report here the first experimental study of femtosecond time-resolved molecular multiphoton ionization.
Femtosecond pump-probe techniques are combined with time-of-flight spectroscopy to measure
transient ionization spectra of Na_2 in a molecular-beam experiment. The wave-packet motions in
different molecular potentials show that incoherent contributions from direct photoionization of a singly
excited state and from excitation and autoionization of a bound doubly excited molecular state determine
the observed ...
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Relativistic Dirac-Fock-Slater program to calculate potential-energy curves for diatomic molecules
(1986)
A LCAO-MO (linear combination of atomic orbitals - molecular orbitals) relativistic Dirac-Fock-Slater program is presented, which allows one to calculate accurate total energies for diatomic molecules.
Numerical atomic Dirac-Fock-Slater wave functions are used as basis functions. All integrations as well as the solution of the Poisson equation are done fully numerical, with a relative accuracy of 10{^-5} - 10{^-6}. The details of the method as well as first results are presented here.
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Delocalization of a hole in van der Waals clusters: Ionization potential of rare-gas and small Hg_n clusters
(American Physical Society, 1993)
The size dependence of the ionization potential I_p(n) of van der Waals (vdW) bound clusters has been calculated by using a model Hamiltonian, which includes electron hopping, vdW interactions, and charge-dipole interactions. The charge-density and dipole-density distributions for both neutral and ionized n-atom clusters are determined self-consistently. The competition between the polarization energy of the neutral atoms surrounding a partially localized hole and the tendency toward hole delocalization in the ionized ...
Aufsatz
Squeezed thermal phonons precurse nonthermal melting of silicon as a function of fluence
(2013)
A femtosecond-laser pulse can induce ultrafast nonthermal melting of various materials along pathways
that are inaccessible under thermodynamic conditions, but it is not known whether there is any structural
modification at fluences just below the melting threshold. Here, we show for silicon that in this regime the
room-temperature phonons become thermally squeezed, which is a process that has not been reported
before in this material. We find that the origin of this effect is the sudden femtosecond-laser-induc ...
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Theoretical study of the structural dependence of nuclear quadrupole frequencies in high-T_c superconductors
(American Physical Society, 1989)
The remarkable difference between the nuclear quadrupole frequencies v_Q of Cu(1) and Cu(2) in YBa_2Cu_3O_6 and YBa_2Cu_3O_7 is analyzed. We calculate the ionic contribution to the electric field gradients and estimate, by using experimental results for Cu_2O and La_2CuO_4, the contribution of the d valence electrons. Thus, we determine v_Q1, v_Q2, and the asymmetry parameter η for YBa_2Cu_3O_6 and YBa_2Cu_3O_7. The number of holes in dthe Cu-O planes and chains is found to be important for the different behavior of ...
Aufsatz
Theory for the Photoacoustic Response to X-Ray Absorption
(American Physical Society, 1988)
A microscopic theory is presented for the photoacoustic effect induced in solids by x-ray absorption. The photoacoustic effect results from the thermalization of the excited Auger electrons and photoelectrons. We explain the dependence of the photoacoustic signal S on photon energy and the proportionality to the x-ray absorption coefficient in agreement with recent experiments on Cu. Results are presented for the dependence of S on photon energy, sample thickness, and the electronic structure of the absorbing solid.