arXiv subjects

Sjard Ole Krüger

Publications and source records attributed to Sjard Ole Krüger.

7 recordsLinked to original sources

arXiv2024

Energy states of Rydberg excitons in finite crystals: From weak to strong confinement

Due to quantum confinement, excitons in finite-sized crystals behave rather differently than in bulk materials. We investigate the dependence of energies of Rydberg excitons on the strengths of parabolic as well as rectangular confinement potentials in finite-sized crystals. The evolution of the energy levels of hydrogen-like excitons in the crossover region from weak to strong parabolic confinement is analyzed for different quantum numbers by numerical solution of the two-dimensional Schrödinger equation. The energy spectrum of hydrogen-like excitons in Cu$_{2}$O-based rectangular quantum wells is, in turn, obtained numerically from the solution of the three-dimensional Schrödinger equation as a function of the quantum well width. Various crossings and avoided crossings of Rydberg energy levels are observed and categorized based on the symmetry properties of the exciton wave function. Particular attention is paid to the two limiting cases of narrow and wide quantum wells attributed to strong and weak confinement, respectively. The energies obtained with the pure Coulomb interaction are compared with the results originating from the Rytova-Keldysh potential, i.e., by taking into account the dielectric contrast in the quantum well and in the barrier.

cond-mat.mes-hall↗

arXiv2021

Interseries dipole transitions from yellow to green excitons in cuprous oxide

We study dipole interseries transitions between the yellow and green exciton series in cuprous oxide including the complex valence band structure. To this end, we extend previous studies of the spectrum of complex green exciton resonances [Phys. Rev. B 101, 075208 (2020)] to optical transitions between different exciton states in addition to transitions from the crystal ground state. This allows us to augment the calculations on interseries transitions using a hydrogen-like model [Phys. Rev. B 100, 085201 (2019)] by a more comprehensive treatment of the valence band structure.

cond-mat.mes-hall↗

arXiv2020

Interaction of charged impurities and Rydberg excitons in cuprous oxide

We investigate the influence of a static, uncorrelated distribution of charged impurities on the spectrum of bound excitons in the copper oxide Cu$_{\text{2}}$O. We show that the statistical distribution of Stark shifts and ionisation rates leads to the vanishing of Rydberg resonances into an apparent continuum. The appearance of additional absorption lines due to the broken rotational symmetry, together with spatially inhomogeneous Stark shifts, leads to a modification of the observed line shapes that agree qualitatively with the changes observed in the experiment.

cond-mat.mes-hall↗

arXiv2019

Interaction of OAM light with Rydberg excitons: Modifying dipole selection rules

Orbital angular momentum (OAM) light possesses in addition to its usual helicity ($s=\pm \hbar$, depending on its circular polarization) an orbital angular momentum $l$. This means that in principle one can transfer more than a single quantum of $\hbar$ during an optical transition from light to a quantum system. However, quantum objects are usually so small (typically in the nm range) that they only locally probe the dipolar character of the local electric field. In order to sense the complete macroscopic electric field, we utilize Rydberg excitons in the semiconductor cuprite ($\text{Cu}_2\text{O}$), which are single quantum objects of up to $μm$ size. Their interaction with focused OAM light, allows for matching the focal spot size and the wavefunction diameter. Here, the common dipole selection rules ($Δj=\pm 1$) should be broken, and transitions of higher $Δj$ with higher order OAM states should become more probable. Based on group theory, we analyze in detail the optical selection rules governing this process. Then we are able to predict what kind of new exciton transitions (quantum number $n$ and $l_{\text{exc}}$) one would expect in absorption spectroscopy on $\text{Cu}_2\text{O}$ using different kinds of OAM light.

physics.optics↗

arXiv2019

Interseries transitions between Rydberg excitons in Cu$_{\mathrm{2}}$O

We investigate the infrared optical transitions between excitons of the yellow, green and blue series in the cuprous oxide Cu$_{\mathrm{2}}$O. We show that in many cases the dipole approximation is inadequate and, in particular, that it breaks down in yellow-blue transitions even for moderate principal quantum numbers of $n \approx 10$. The interband matrix elements of the transition operator needed for the evaluation of the excitonic transition strengths are derived from known as well as from fitted band parameters.

cond-mat.mes-hall↗

arXiv2018

Interactions between Rydberg excitons in Cu$_2$O

Highly-excited states of excitons in cuprous oxide have recently been observed at a record quantum number of up to $n=25$. Here, we evaluate the long-range interactions between pairs of Rydberg excitons in Cu$_2$O, which are due to direct Coulomb forces rather than short-range collisions typically considered for ground state excitons. A full numerical analysis is supplemented by the van der Waals asymptotics at large exciton separations, including the angular dependence of the potential surfaces.

cond-mat.quant-gas↗

arXiv2018

Waveguides for Rydberg excitons in Cu$_\text{2}$O from strain traps

We investigate the formation of waveguides for Rydberg excitons in Cu$_\text{2}$O from cylindrical stressors as alternatives to optical traps. We show that the achievable potential depths can easily reach the meV and the trap frequencies the GHz regimes. For Rydberg excitons, we find that it is sufficient to consider only the shift of the band gap, whereas the excitonic binding energies remain almost unchanged.

cond-mat.mes-hall↗