Search results for "Quasiparticle"
showing 10 items of 280 documents
Charge-exchange reactions on double-βdecaying nuclei populatingJπ=2−states
2017
The $(\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He},t)$ charge-exchange reaction populating ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$ states has been examined at 420 MeV incident energy for a series of double-$\ensuremath{\beta}$ decaying nuclei, i.e., $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{96}\mathrm{Zr}$, $^{100}\mathrm{Mo}$, $^{128}\mathrm{Te}$, $^{130}\mathrm{Te}$, and $^{136}\mathrm{Xe}$. The measurements were carried out at the Grand Raiden spectrometer of the Research Center for Nuclear Physics at the University Osaka with typical spectral resolution of 30--40 keV. It is found that the charge-exchange reaction leading to ${2}^{\ensuremath{-}}$ spin-dipole states is selective to…
Ab-Initio Studies of Electronic and Spectroscopic Properties of MgO, ZnO and CdO
2008
We present ab-initio calculations of excited-state properties within single-particle and two-particle approaches in comparison with corresponding experimental results. For the theoretical treatment of the electronic structure, we compute eigenvalues and eigenfunctions by using a spatially nonlocal exchange-correlation potential. From this starting point, quasiparticle energies within the fully frequency-dependent G(0)W(0) approximation are obtained. By solving the Bethe-Salpeter equation, we evaluate optical properties, including the electron-hole attraction and the local-field effects. The results are compared with experimental spectra from soft X-ray emission, as well as from X-ray photoe…
Transitions in the Quasiparticle Picture
2007
In this chapter we deal with electromagnetic and beta-decay transitions in terms of independent quasiparticles. Transition amplitudes are derived for transitions between one-quasiparticle states and between two-quasiparticle states. Derivations and applications are made within the BCS framework, but the expressions for the amplitudes are valid also in the LNBCS description.
Skyrmion Dynamics – from thermal diffusion to ultra-fast motion
2018
Summary form only given. Spintronics promises to be a paradigm shift from using the charge degree of freedom to using the spin degree of freedom. To this end three key requirements are: (i) stable spin structures for long term data retention; (ii) efficient spin manipulation for low power devices and (iii) ideally no susceptibility to stray fields as realized for antiferromagnets. We explore different materials classes to tackle these challenges and explore the science necessary for a disruptive new technology. To obtain ultimate stability, topological spin structures that emerge due to the Dzyaloshinskii-Moriya interaction (DMI), such as chiral domain walls and skyrmions are used. These po…
Coulomb excitation of re-accelerated 208Rn and 206Po beams
2013
In the present study, B( E2; 2(+)-> 0(+) ) values have been measured in the Rn-208 and Po-206 nuclei through Coulomb excitation of re-accelerated radioactive beams in inverse kinematics at CERN-ISOLDE. The resulting B(E2; 2(+)-> 0(+)) in 208Rn is similar to 0.08 e(2)b(2). These nuclei lie in, or at the boundary of the region where seniority scheme should persist. However, contributions from collective excitations may be present when moving away from the N = 126 shell closure. To date, surprisingly little is known of the transition probabilities between the low-spin states in this region.
Spin-multipole nuclear matrix elements in thepnquasiparticle random-phase approximation: Implications forβandββhalf-lives
2017
Half-lives for 148 potentially measurable 2nd-, 3rd-, 4th-, 5th-, 6th-, and 7th-forbidden unique beta transitions are predicted. To achieve this, the ratio of the nuclear matrix elements (NMEs), calculated by the proton-neutron quasiparticle random-phase approximation (pnQRPA), ${M}_{\mathrm{pnQRPA}}$, and a two-quasiparticle (two-qp) model, ${M}_{\mathrm{qp}}$, is studied and compared with earlier calculations for the allowed Gamow-Teller (GT) ${1}^{+}$ and first-forbidden spin-dipole (SD) ${2}^{\ensuremath{-}}$ transitions. The present calculations are done using realistic single-particle model spaces and $G$-matrix based microscopic two-body interactions. In terms of the ratio $k={M}_{\m…
Kadanoff-Baym approach to quantum transport through interacting nanoscale systems: from the transient to the steady-state regime
2009
We propose a time-dependent many-body approach to study the short-time dynamics of correlated electrons in quantum transport through nanoscale systems contacted to metallic leads. This approach is based on the time-propagation of the Kadanoff-Baym equations for the nonequilibrium many-body Green's function of open and interacting systems out of equilibrium. An important feature of the method is that it takes full account of electronic correlations and embedding effects in the presence of time-dependent external fields, while at the same time satisfying the charge conservation law. The method further extends the Meir-Wingreen formula to the time domain for initially correlated states. We stu…
Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque
2020
We investigate the influence of magnons on the temperature-dependence and the anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order perturbation theory in the framework of the Keldysh formalism in order to derive suitable equations to compute the magnonic SOT. We find several contributions to the magnonic SOT, which depend differently on the spin-wave stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba parameters the magnonic SOT is strongly anisotropic and for small quasiparticle broadening it m…
Unidirectional Magnon-Driven Domain Wall Motion Due to the Interfacial Dzyaloshinskii-Moriya Interaction
2018
We demonstrate a unidirectional motion of a quasiparticle without an explicit symmetry breaking along the space-time coordinate of the particle motion. This counterintuitive behavior originates from a combined action of two intrinsic asymmetries in the other two directions. We realize this idea with the magnon-driven motion of a magnetic domain wall in thin films with interfacial asymmetry. Contrary to previous studies, the domain wall moves along the same direction regardless of the magnon-flow direction. Our general symmetry analysis and numerical simulation reveal that the odd order contributions from the interfacial asymmetry is unidirectional, which is dominant over bidirectional contr…
Electric Control of Dirac Quasiparticles by Spin-Orbit Torque in an Antiferromagnet
2016
Spin-orbitronics and Dirac quasiparticles are two fields of condensed matter physics initiated independently about a decade ago. Here we predict that Dirac quasiparticles can be controlled by the spin-orbit torque reorientation of the N\'{e}el vector in an antiferromagnet. Using CuMnAs as an example, we formulate symmetry criteria allowing for the co-existence of Dirac quasiparticles and N\'{e}el spin-orbit torques. We identify the non-symmorphic crystal symmetry protection of Dirac band crossings whose on and off switching is mediated by the N\'{e}el vector reorientation. We predict that this concept, verified by minimal model and density functional calculations in the CuMnAs semimetal ant…