SearcharxivSearch

arXiv subjects

Helmut Zacharias

Publications and source records attributed to Helmut Zacharias.

3 recordsLinked to original sources

A Chirality-Based Quantum Leap

Chiral degrees of freedom occur in matter and in electromagnetic fields and constitute an area of research that is experiencing renewed interest driven by recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials. The CISS effect underpins the fact that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision. Any technology that relies on optimal charge transport, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which is presently lacking. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking perspective provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and presents a vision for their future roles in enabling room-temperature quantum technologies.

cond-mat.mes-hall

Nonlinear coherence effects in transient-absorption ion spectroscopy with stochastic extreme-ultraviolet free-electron laser pulses

We demonstrate time-resolved nonlinear extreme-ultraviolet absorption spectroscopy on multiply charged ions, here applied to the doubly charged neon ion, driven by a phase-locked sequence of two intense free-electron laser pulses. Absorption signatures of resonance lines due to 2$p$--3$d$ bound--bound transitions between the spin-orbit multiplets $^3$P$_{0,1,2}$ and $^3$D$_{1,2,3}$ of the transiently produced doubly charged Ne$^{2+}$ ion are revealed, with time-dependent spectral changes over a time-delay range of $(2.4\pm0.3)\,\text{fs}$. Furthermore, we observe 10-meV-scale spectral shifts of these resonances owing to the AC Stark effect. We use a time-dependent quantum model to explain the observations by an enhanced coupling of the ionic quantum states with the partially coherent free-electron-laser radiation when the phase-locked pump and probe pulses precisely overlap in time.

physics.atom-ph

Spin-flip scattering in chiral induced spin selectivity using the Riccati equation

The chiral induced spin selectivity (CISS) in layers of helical molecules gained considerable attention in the emerging field of spintronics, because the effect enables spin-filter devices under ambient conditions. Several theoretical studies have been carried out to explain this effect on a microscopic scale, but the origin of the effect is still controversial. In particular the role of spin-flip scattering during electron transport is an open issue. In this study we describe the electron and spin transport by rate equations including spin-dependent losses and spin-flip scattering. We reduce the problem to the solution of the Riccati differential equation to obtain analytical solutions. The results allow to determine and interpret the strength and scalability of CISS based spin-filters from experimental data or quantum mechanical models. For the helical systems studied experimentally so far it turns out that spin-flip scattering plays a minor role.

cond-mat.mes-hall