A twisted X-ray beam with orbital angular momentum is employed in a theoretical study to probe molecular chirality. A nonlocal response description of the matter-field coupling is adopted to account for the field short wavelength and the structured spatial profile. We use the minimal-coupling Hamiltonian, which implicitly takes into account the multipole contributions to all orders. The combined interactions of the spin and orbital angular momentum of the X-ray beam give rise to circular-helical dichroism signals, which are stronger than ordinary circular dichroism signals, and may serve as a useful tool for the study of molecular chirality in the X-ray regime.

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The spin-polarized scanning tunneling microscope (SP-STM) has served as a versatile tool for probing and manipulating the spintronic properties of atomic and molecular devices with high precision. The interplay between the local spin state and its surrounding magnetic environment significantly affects the transport behavior of the device. Particularly, in the contact regime, the strong hybridization between the SP-STM tip and the magnetic atom or molecule could give rise to unconventional Kondo resonance signatures in the differential conductance (dI/dV) spectra. This poses challenges for the simulation of a realistic tip control process. By combining the density functional theory and the hierarchical equations of motion methods, we achieve first-principles-based simulation of the control of a Ni-tip/Co/Cu(100) junction in both the tunneling and contact regimes. The calculated dI/dV spectra reproduce faithfully the experimental data. A cotunneling mechanism is proposed to elucidate the physical origin of the observed unconventional Kondo signatures.

We propose an interferometric pump-probe technique that employs three entangled photons generated by cascaded spontaneous parametric downconversion. A Mach–Zehnder interferometer made of two three-port waveguide arrays is inserted in the optical path. Two independent phases introduced to manipulate the entangled photon state serve as control parameters and can selectively excite matter pathways. Compared to two-photon-absorption of an entangled photon-pair, the three-photon signals are significantly enhanced by frequency-dispersed photon-counting detection.

Fine-tuning the magnetic anisotropy energy (MAE) of a magnetic molecule with a high precision of sub-meV has been realized experimentally by manipulating the tip of a scanning tunneling microscope (STM). Understanding the mechanisms behind the observed evolution of spin excitation energy is essentially important for potential spintronic applications. In particular, it is crucial to unveil the influence of the surrounding environment on the molecular spin state. To this end, we carry out the first-principles simulation on the STM-tip control of an iron octaethylporphyrin chloride (Fe-OEP-Cl) molecule adsorbed on the Pb(111) substrate. By carefully taking into account the atomic structures of the tip and the substrate as well as the multireference feature of the Fe 3d electrons, the experimentally measured evolution of spin excitation energy, including a continuous increase, followed by a sudden drop in the MAE, is accurately reproduced by our simulation with a maximal discrepancy of less than 0.3 meV. Based on a comprehensive analysis of the change in geometric and electronic structures of the whole single-molecule junction, the exotic evolution of MAE is attributed to the variation of the ligand confinement effect and the resulting charge transfer. The unique role of the single-atomic Cl ligand is clarified by comparing the evolution under the STM-tip control with that of the tip/Fe-OEP/Pb(111) junction. The theoretical insights provided by this work would be valuable for the on-demand design of the mechanically controlled magnetic nanojunctions.