Physica E-low-dimensional Systems & Nanostructures最新文献

We have developed a theory of cooperative photoluminescence from two closely spaced particles using the density matrix method. The theory provides simulations of the photoluminescence excitation and emission spectra by nonidentical quantum emitters entangled by the dipole–dipole interaction in presence of a cw laser beam. The excitation spectra are shown to be consistent with all known experiments to date with pairs of coherently coupled organic molecules in thin solid layers. The simulations were performed with the use of the Bogoliubov–Born–Green–Kirkwood–Yvon (BBGKY) hierarchies for reduced density matrices and correlation operators of the quantum emitters and photonic subsystems. This method gives a straightforward way to describe the dipole–dipole coupling and entanglement of the emitters. We have also calculated the emission spectra to demonstrate the expected spectral patterns.

Understanding lithium (Li) adsorption in silicon quantum dots (SiQDs) is crucial for optimizing Li-ion battery (LIB) anode materials. We systematically investigated Li adsorption in ten hydrogenated SiQDs (Si₁₀H₁₆, Si₁₄H₂₀, Si₁₈H₂₄, Si₂₂H₂₈, Si₂₆H₃₀, Si₃₀H₃₄, Si₃₅H₃₆, Si₃₉H₄₀, Si₄₄H₄₂, and Si₄₈H₄₆) across five adsorption sites (bridge(B), on-top(T), hollow-tetrahedral inner(Td_inner), hollow-tetrahedral surface(Td_surface), and hollow-hexagonal(Hex)), utilizing density functional theory (DFT) with the M06–2X hybrid functional and 6-31G+(d) basis set. Findings identify Td_inner as the most favorable adsorption site, with a binding energy (E_bind) of 0.80–1.00 eV, dependent on SiQD size. The adsorption site exerts a more pronounced impact on E_bind than the cluster size. Multiple adsorptions in SiQDs show increased E_bind per Li atom with Li atom number. Molecular volume changes, independent of Li atom number but site-dependent, exhibit a maximum of 2.51 %. SiQD energy gap, influencing conductivity, varies with size, larger SiQDs being more conductive, especially with Li adsorption. Conclusively, our study recommends large-sized SiQDs as optimal LIB anode materials, offering high capacity, minimal volume expansion, and reasonable conductivity. This research addresses a theoretical gap, illuminating the impact of Li adsorption on SiQD molecular volumes and electronic structures, aiding in the design of enhanced capacity silicon anodes for LIB.

Bound states in the continuum (BICs) are quantum states with normalizable wave functions and energies that lie within the continuous spectrum for which extended or dispersive states are also available. These special states, which have shown great applicability in photonic systems for devices such as lasers and sensors, are also predicted to exist in electronic low-dimensional solid-state systems. The non-trivial topology of materials is within the known mechanisms that prevent the bound states to couple with the extended states. In this work we search for topologically protected BICs in a quantum Hall bar with an anti-dot formed by a pore far from the borders of the bar. The bound state energies and wavefunctions are calculated by means of the Recursive S-Matrix method. The resulting bound state energies coexist with extended states and exhibit a pattern complimentary to the Hofstadter butterfly. A symmetry-breaking diagonal disorder was introduced, showing that the BICs with energies far from the Landau levels remain robust. Moreover, the energy difference between consecutive BICs multiplied by the anti-dot perimeter follows the same curve despite disorder. Finally, a BIC-mediated current switching effect was found in a multi-terminal setup for zero and finite temperature, which might permit their experimental detection.

Studies of mesoscopic structures have become a leading and rapidly evolving research field ranging from physics, chemistry, and mineralogy to life sciences. The increasing miniaturization of devices with length scales of a few nanometers is leading to radical changes in the realization of new materials and in shedding light on our understanding of the fundamental laws of nature that govern the dynamics of systems at the mesoscopic scale. We investigate thermodynamic processes in small systems in Onsager’s region based on recent experimental results and previous theoretical research. We show that fundamental quantities such as the total entropy production, the thermodynamic variables conjugate to the thermodynamic forces, and the Glansdorff–Prigogine’s dissipative variable may be discretized at the mesoscopic scale. We establish the canonical com- mutation rules (CCRs) valid at the mesoscopic scale. The numerical value of the discretization constant is estimated experimentally. The ultraviolet divergence problem is solved by applying the correspondence principle with Einstein–Prigogine’s fluctuations theory in the limit of macroscopic systems. Examples of quantization of thermodynamic systems out of the Onsager region are currently being finalized.

Spintronic devices with enhanced spin quantum transport are crucial for future computing technology. Here we investigate the magnetic, electro-optical, and transport properties of 2D chains from laterally connected zigzag triangular graphene (ZTG) nanodots using first principle calculations. The optimized structures show that ZTG connected with an even number of C-atoms have a planer structure while those linked with odd numbers experience noticeable twisting. The twisting can be removed by considering the effect of the substrate due to van der Waals interactions with the substrate. Vibrational frequencies and binding energies confirmed the structural stability of the considered ZTG chains. The ZTG chains have ferromagnetic spin ordering proportional to the number of linked ZTG that can even increase in odd-linked chains due to the unpaired electrons from the odd link. For instance, 3ZTG coupled by an even link (2C) is a ferromagnetic chain coupled by a nonmagnetic link while odd linking (3C) results in a ferromagnetic chain with higher net spin and ferromagnetic coupling. The I–V curves indicate that the current in the latter chain is significantly higher than that in the former, especially for the spin-up current. Moreover, its transmission spectra reveal only one sharp spin-up peak within the bias window at an applied voltage of 1.5 V. Therefore, the considered ZTG chains with odd links are promising spin filters for spintronic applications.

Integration of two-dimensional materials into van der Waals heterostructures (vdWHs) provides advantages in terms of structural flexibility, interfacial modulation capabilities, and diverse device designs. We constructed the WTe₂/WSi₂As₄ vdWHs and explored the electronic and optical properties in detail, revealing the modulation behavior for electronic structure of WTe₂/WSi₂As₄ by applied electric field and biaxial strain. The intrinsic heterostructures exhibits a type I band alignment with a direct band gap of 0.701 eV, covering the optical absorption properties from the infrared to the ultraviolet range with absorption coefficients up to 10⁵. In particular, the WTe₂/WSi₂As₄ vdWHs can transition from a type I to type II band alignment in the presence of an external electric field. The present work provides directions for tunable multi-band alignment in WTe₂/WSi₂As₄ vdWHs, contributing to high-efficiency photodetectors and multipurpose optoelectronic device applications.

We study the quantum dynamics of an electron subject to the Dresselhaus spin–orbit interaction (SOI) and few magnetic impurities confined in a narrow semiconductor quantum ring. The exchange interaction between the electron and the magnetic Mn impurities is modeled via a Kondo-like Hamiltonian. The role of the Dresselhaus SOI is to mediate between the orbital and spin angular momentum of the electron. Our goal is to explore and analyze in the time domain the transference of angular momentum between the electron and the system of Mn impurities. We aim to contribute to the search for mechanisms that facilitate the effective magnetization of the impurity system via the interaction with charge carriers, without the use of external magnetic fields. We pose and numerically solve the equations of motion of the reduced density matrix for our multiparticle system, resorting to a state-of-the-art truncation scheme. We first obtain the dynamics without the SOI and show how the Mn impurities strongly modify the electronic angular momentum. Secondly, we add the SOI and describe the competition that occurs between the two interaction mechanisms. In our analysis, we profit from the fact that for a one-dimensional quantum ring with only SOI the Hamiltonian reduces to block-diagonal form and the exchange interaction couples rather weakly different blocks. As general trends, we find that the SOI slows down the magnetization of the impurities and superimposes rapid oscillations in the evolution of the electron’s orbital angular momentum.

In this study, CNNZO (N–ZnO/g-C₃N₄) nanocomposites were synthesized via a facile hydrothermal method and characterized using XRD, FTIR and FESEM. The resulting N–ZnO nano-needles and plate-like structures, anchored onto g-C₃N₄ agglomerates, formed distinctive nano-flower topography. CNNZO demonstrated superior photocatalytic activity compared to CN and N–ZnO, achieving ∼98 % degradation of Methylene Blue, 85.53 % of Methyl Green and 87.29 % of Methyl Orange under visible light irradiation within 90 min. This enhanced performance is attributed to the unique morphology of CNNZO, which promotes efficient charge carrier transfer and inhibits recombination. Additionally, CNNZO exhibited improved electrocatalytic activity with smaller HER and OER potentials. This study underscores the potential of CNNZO nanocomposites as effective catalysts for the degradation of organic contaminants and hydrogen and oxygen evolution for energy production.

We show that the authors of a paper published recently failed to obtain the thermodynamic properties of the system (Helmholtz free energy, entropy, internal energy, specific heat, magnetization and magnetic susceptibility). The reason is that they omitted the sum over the magnetic quantum number which is essential for the calculation of the partition function. As a consequence, their analytical expressions are unsuitable for any physical application.