Two-photon magneto-optical transitions in quantum rings

In this study, for the first time, the combined effects of external magnetic, electric, and Aharonov-Bohm (AB) flux fields on quantum levels of the hydrogen atom embedded in Debye and quantum plasmas modeled by the more general exponential cosine screened Coulomb (MGECSC) potential are investigated within cylindrical coordinate formalism using the asymptotic iteration method. The MGECSC potential includes four different potential forms when considering different sets of the parameters in the potential. The corresponding Schrödinger equation is solved numerically in order to examine both strong and weak regimes and confinement effects of external fields. The influence of screening parameters of the MGECSC potential on quantum levels of the hydrogen atom is also studied in detail in the presence of external magnetic, electric, and AB flux fields. As it is possible to model both Debye and quantum plasmas by using screening parameters in the MGECSC potential, the effects of each plasma environment on quantum levels of the hydrogen atom are also considered in the external fields. It is observed that there are important results of external fields on the total interaction potential profile, and the most dominant one in these fields is the magnetic field. Furthermore, the effects of confinement on the physical state of the plasma environment is a subject of this study. These details would be important in experimental and theoretical investigations in plasma and atomic physics fields.

Quantum description of the isothermal and adiabatic magnetocaloric effect (MCE), thermomagnetic properties, and energy spectra of three diatomic molecules, namely: lithium hydride (LiH), titanium hydride (TiH), and scandium hydride (ScH), was examined with Deng-Fan-Screened Coulomb Potential using the Greene-Aldrich approximation to the centrifugal term. The numerical solutions of the proposed potential with and without the magnetic and AB flux fields obtained reveal that the combined impacts of the magnetic and AB flux fields completely remove the degeneracy of the energy spectra and control the behaviour of the MCE by acting as a regulating factor to cool or heat the MCE. Also, the proposed potential reduces to three exceptional cases, and the thermomagnetic plots obtained for the analysed dimer molecules agreed perfectly with previous work. This research has the potential to be applied in molecular physics and MCE studies for a variety of molecules.

We present a more general form of the Schrodinger equation in curved space by introducing the magnetic fields. Further, we solve the non-relativistic wave equation with the radial scalar power potential (RSPP) under the influence of magnetic and Aharonov-Bohm (AB) flux fields by using the curvilinear coordinates system in such space. With this requirement, the energy spectrum and the corresponding wave functions have been calculated by means of the series method. Our analytical results are compared with other results and found to be in a good agreement. Furthermore, the main thermodynamic functions, such as the free energy, the mean energy, the entropy, the specific heat, the persistent currents and the magnetization, have been calculated by using the characteristic function. Some plots of the numerical results of the thermodynamic quantities are shown. Finally, we discuss our results.

The influence of external magnetic and Aharonov‐Bohm (AB) flux fields on the energy spectra and thermal properties of N2, NO, CO and H2 diatomic molecules are investigated in this study. The two‐dimensional Schrödinger equation is solved with the Varshni‐screened Coulomb potential (VSCP) model using the well‐known Nikiforov‐Uvarov (NU) method. We obtained the energy eigenvalues and wavefunctions of the system and calculated the energy levels of some diatomic molecules in the m‐arbitrary state in the presence and absence of external magnetic and AB flux fields. The results show that combining the magnetic and AB flux fields eliminates degeneracy. We analyzed and plotted the partition function and other thermal properties in the presence of a magnetic field, an AB field, and a temperature‐dependent term.

PDM-charged particles in PD-magnetic plus Aharonov–Bohm flux fields: Unconfined “almost-quasi-free” and confined in a Yukawa plus Kratzer exact solvability

Since the discovery of high-order harmonic generation (HHG) in solids, much effort has been devoted to understanding its generation mechanism and both interband and intraband transitions are known to be essential. However, intraband transitions are affected by the electronic structure of a solid, and how they contribute to nonlinear carrier generation and HHG remains an open question. Here, we use mid-infrared laser pulses to study HHG in CdSe and CdS quantum dots (QDs), where quantum confinement can be used to control the intraband transitions. We find that both the HHG intensity per excited volume and the generated carrier density increase when the average QD size is increased from about 2 nm to 3 nm. We show that the reduction of the subband gap energy in larger QDs enhances intraband transitions, and this in turn increases the rate of photocarrier injection by coupling with interband transitions, resulting in enhanced HHG.

Topological defect and external fields influence on potential models has been significantly proven to shape the behaviour and interactions of different constituent quantum systems. Due on this fact, we employ the Nikiforov-Uvarov functional analysis method to solve the Schrödinger equation with Hulthén-Hellmann Potential, embedded with Aharonov-Bohm flux field and point-like global monopole defect. Analytical expression of the energies with topological defect and AB flus field was obtained. In addition, the scattering phase shift expression of the combined potential was obtained under the influence of the global monopole and external field. Numerical and graphical variations have been presented for various quantum states, flux field and topological defect values. It is observed that, energy eigenvalues and scattering phase shift of the combined potential are significantly affected by the topological defect parameters, Aharonov-Bohm flux field, screening parameter and quantum state values considered, in the curved space-time. Conventional results of this study in Minkowski space-time are realized as the topological defect parameter approaches unity, in the absence of the AB flux field and these results agree with available results in literature. The results in this study also point relatively to some physical phenomena in chemical and molecular physics.

In the bcc transition metals Cr, Mo, and W, the existence of the partially filled d bands makes interband transition occur at low photon frequencies and thus, it is difficult to differentiate it from intraband transition. Here, we present a thorough study on decomposing the intraband and interband contribution to finite temperature dielectric functions of these bcc transition metals by performing electron-phonon and electron-electron interaction calculations, as well as ellipsometry experiments. In this work, the Drude model and interband transition theory are applied to quantitatively describe the intraband and interband transition, respectively. To accurately determine intraband transition, the relevant parameters for the Drude model, such as plasma frequency and electron relaxation time, are calculated from first-principles. The electron-electron interaction within the many-body theory and electron-phonon interaction within the density functional perturbation theory are calculated to obtain the electron relaxation time and intraband dielectric function at finite temperature. As for interband transition, the spin-orbit coupling is included and it shows nontrivial influence on the interband dielectric function of Mo and W, especially at low frequencies. To verify theoretical calculations, ellipsometry experiments are performed to measure dielectric functions of Cr, Mo, and W over the temperature range of 300–700 K and energy range of 0.08–4.8 eV. The experimental results are then fitted by the Drude model, and it shows that the electron-phonon interaction rather than electron-electron interaction dominates the frequency dependence of the relaxation time for transition metals Cr, Mo, and W.

We investigated the transmission probability of a single electron transmission through a quantum ring device based on the single-band effective mass approximation method and transfer matrix theory. The time-dependent Schrödinger equation is applied on a Gaussian wave packet passing through the quantum ring system. The electron tunneling resonance peaks split when the electron transmits through a double quantum ring. The splitting energy increases as the distance between the two quantum rings decreases. We studied the tunneling time through the single electron transmission quantum ring from the temporal evolution of the Gaussian wave packet. The electron probability density is sensitive to the thickness of the barrier between the two quantum rings.

We investigate theoretically the size-dependence of two-photon absorption (TPA) for circular graphene quantum dots (GQDs) on the basis of electronic energy states obtained by solving the Dirac-Weyl equation analytically under infinite-mass boundary condition. The analytical expressions for TPA coefficient are derived with an arbitrary size-distribution and the transition selection rules are obtained. Results reveal that the intraband transitions in conduction band and valence band contribute much more to TPA than interband transitions. The energy spectrum and TPA peaks are tuned by the size of GQDs.

This study presents a numerical and computational investigation into the energy fluctuations of three diatomic molecules—carbon monoxide (CO), hydrogen (H₂), and scandium hydride (ScH)— under a varying temperature parameter β based on two – dimension Schrödinger equation governed by Nikiforov – Uvarov Functional Analysis (NUFA) approach under the influence of magnetic field and magnetic flux. The numerical analysis indicates that when no external magnetic field is applied B = 0T and AB = 0, the energy spectrum experiences a slight increase. However, a higher energy spectrum is observed when an external field is introduced at ∅AB = 9 and B = 9 T. Examining the individual effects reveals that ∅AB = 9 and B = 0 T have a somewhat stronger impact on the energy spectrum compared to B = 0T, and ∅AB = 0 has a limited effect on the overall energy spectrum. Additionally, it was numerically demonstrated that the energy levels remain consistent across three diatomic molecules, regardless of changes in the magnetic quantum number. Furthermore, shifts were noted in orbitals (s, p, d, f), which are uniformly affected by external variables. The values of these orbitals decrease as the orbital quantum number (n) increases, following the expected sequence: s > p > d > f. Computational findings, derived from a thermodynamic approach using partition analysis, show a reduction in the partition function when plotted against temperature, influenced by the magnetic field and flux. It was also observed that both molecules exhibit heightened energy fluctuations as the magnetic field strength and flux increase. The study underscores the critical role of external magnetic factors in shaping molecular energy behaviour through entropy, internal energy, free energy, specific heat capacity and energy fluctuation across various temperature ranges.

Optical absorption spectra of GaSb/GaAs quantum-ring-with-dot structures (QRDSs) are calculated using Fermi’s golden rule by which the electronic states involved in the optical transitions are obtained from the eight-band k ⋅ p method. The absorption spectra of multi-stacked QRDS layers show that the interband and intraband transitions are favorable to intermediate band solar cells (IBSCs). A drift-diffusion model with rate equations for a solar cell containing multi-stacked QRDS layers is formulated based on the absorption spectra. The external quantum efficiency (EQE) determined by the model with the AM1.5 solar spectrum and additional infrared light demonstrates that the confined hole states in the quantum ring (QR) parts of the QRDSs effectively function as an IB. The more efficient two-step photon absorption indicated by the enhancement of the EQE also suggests the potential of QRDSs for the IBSCs.

We investigate the electron states and optical absorption in square- and hexagonal-shaped two-dimensional (2D) HgTe quantum dots and quantum rings in the presence of a perpendicular magnetic field. The electronic structure is modeled by means of the $s{p}^{3}{d}^{5}{s}^{*}$ tight-binding method within the nearest-neighbor approximation. Both bulklike and edge states appear in the energy spectrum. The bulklike states in quantum rings exhibit Aharonov-Bohm oscillations in magnetic field, whereas no such oscillations are found in quantum dots, which is ascribed to the different topology of the two systems. When magnetic field varies, all the edge states in square quantum dots appear as quasibands composed of almost fully flat levels, whereas some edge states in quantum rings are found to oscillate with magnetic field. However, the edge states in hexagonal quantum dots are localized like in rings. The absorption spectra of all the structures consist of numerous absorption lines, which substantially overlap even for small line broadening. The absorption lines in the infrared are found to originate from transitions between edge states. It is shown that the magnetic field can be used to efficiently tune the optical absorption of HgTe 2D quantum dot and quantum ring systems.

The theoretical investigation of interband and intraband transitions in asymmetric ellipsoidal InAs quantum dot have been considered. The interband absorption coefficient dependencies from quantum dot geometrical parameters have been calculated. Linear and nonlinear absorption spectra behaviors have been observed for different geometrical sizes. Also, the second and third harmonic generation coefficients have been studied.

For the first time, exact analytical solutions of electronic wavefunctions in quantum ring-like structures are found using a symmetry-adapted coordinate system. In the case of an infinite potential barrier, it is related to a more general problem of finding resonance modes in a ring-like cavity. The solutions in the parabolic coordinate system are Bessel or confluent hypergeometric functions for quantum dot, ring and wire including objects with flat bases. The continuous evolution from the 0D quantum dot system to the perfect 1D quantum ring system is analysed. The electronic properties (energy levels, wavefunctions and density of states) are continuously followed during the dot to ring transformation until the limit of a perfect 1D quantum ring is reached. The creation of a ring structure by changing the material composition in a dot centre leads to a sharp variation in the energy levels of totally symmetric states. This is a consequence of the immediate build-up of a potential barrier energy in the centre of the ring. Finally the use of the structure of electronic levels to identify the signature of self-organized quantum rings when compared to quantum dots is proposed.