arXiv subjects

Robert Wieser

Publications and source records attributed to Robert Wieser.

7 recordsLinked to original sources

arXiv2026

Exact admissibility radii for the lattice topological charge of quantum spin textures

How much can a magnetic field change before a quantum spin texture loses its skyrmion charge? For a triangulated spin-$s$ texture on $N$ quantum sites, we determine the smallest change in its local moments that makes the reconstructed topological charge ill-defined, allowing unequal error bounds and fixed boundary moments. Combined with spectral perturbation theory, this geometric threshold yields explicit magnetic-field intervals that preserve the ground-state charge, scaling as $1/N$ when the gap and geometric margin have positive limits. We apply the bounds to finite spin-$1/2$ systems with exchange and Dzyaloshinskii-Moriya interactions. In a rigorously verified seven-spin example the charge changes at a single certified field, while the excitation gap and all local spin polarizations remain bounded away from zero; there the geometric margin vanishes linearly.

math-ph↗

arXiv2026

Quantum-classical crossover in finite spin-1/2 rings with Dzyaloshinsky-Moriya interaction

We study finite spin-$\tfrac12$ rings with nearest-neighbor Heisenberg exchange, Dzyaloshinsky--Moriya interaction, and an external magnetic field. We introduce an interpolation parameter between the fully quantum Hamiltonian and a state-dependent mean-field description. Using dissipative Gisin--Schrödinger dynamics, we analyze the resulting quantum--classical crossover through local magnetization, connected spin correlations, single-site entropy, and the saturation field of the fully polarized state.

cond-mat.str-el↗

arXiv2026

Bridging Quantum and Classical Descriptions of Spin Dynamics in a Dzyaloshinsky-Moriya Trimer

The spin dynamics of a trimer with Dzyaloshinsky-Moriya (DM) interaction are investigated within a unified Hamiltonian framework that connects quantum-mechanical and semiclassical descriptions. The interpolation between the two regimes is realised by solving the modified Gisin-Schrödinger equation, in which the relative weight of a quantum coherence and local mean-field contributions is continuously tuned. The resulting dynamical behaviour is analysed and summarised in a ground state diagram that illustrates how the character of the spin motion evolves from fully quantum to semiclassical as the DM interaction is treated at different levels of approximation. In the last part of the publication, the chiral spin dynamics proposed by Da-Wei Wang et al. is examined theoretically, taking into account its behaviour at the boundary between quantum and classical physics.

cond-mat.mes-hall↗

arXiv2016

Derivation of a time dependent Schrödinger equation as quantum mechanical Landau-Lifshitz-Bloch equation

The derivation of the time dependent Schrödinger equation with transversal and longitudinal relaxation, as the quantum mechanical analog of the classical Landau-Lifshitz-Bloch equation, has been described. Starting from the classical Landau-Lifshitz-Bloch equation the transition to quantum mechanics has been performed and the corresponding von-Neumann equation deduced. In a second step the time Schrödinger equation has been derived. Analytical proofs and computer simulations show the correctness and applicability of the derived Schrödinger equation.

cond-mat.mes-hall↗

arXiv2015

Current and field driven domain wall motion under influence of the Dzyaloshinsky-Moriya interaction

A complete analytical description of the dynamics of current and field driven transverse domain walls under the influence of the Dzyaloshinsky-Moriya interaction using the $ϕ- q$ model will be given. Five different scenarios will be observed where the Dzyaloshinsky-Moriya vector is either parallel or perpendicular to the easy axis anisotropy of the system and a direct reversal respectively precessional motion will be assumed.

cond-mat.mes-hall↗

arXiv2014

Quantum spin dynamics

The classical Landau-Lifshitz equation has been derived from quantum mechanics. Starting point is the assumption of a non-Hermitian Hamilton operator to take the energy dissipation into account. The corresponding quantum mechanical time dependent Schrödinger, Liouville and Heisenberg equation have been described and the similarities and differences between classical and quantum mechanical spin dynamics have been discussed. Furthermore, a time dependent Schrödinger equation corresponding to the classical Landau-Lifshitz-Gilbert equation and two ways to include temperature into the quantum mechanical spin dynamics have been proposed.

quant-ph↗

arXiv2012

Information transfer by vector spin chirality in finite magnetic chains

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin-spiral in finite individual bi-atomic Fe chains on the (5x1)-Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of nanometers away, suggesting a new way of transmitting information about the state of magnetic objects on the nanoscale.

cond-mat.mes-hall↗