Scaling laws of Rydberg excitons

Article

关键词: FINE-STRUCTURE;    CU2O;    ABSORPTION;   

DOI  :  10.1103/PhysRevB.96.125142

来源: SCIE

【 摘 要 】

Rydberg atoms have attracted considerable interest due to their huge interaction among each other and with external fields. They demonstrate characteristic scaling laws in dependence on the principal quantum number n for features such as the magnetic field for level crossing or the electric field of dissociation. Recently, the observation of excitons in highly excited states has allowed studying Rydberg physics in cuprous oxide crystals. Fundamentally different insightsmay be expected for Rydberg excitons, as the crystal environment and associated symmetry reduction compared to vacuum give not only optical access to many more states within an exciton multiplet but also extend the Hamiltonian for describing the exciton beyond the hydrogen model. Here we study experimentally and theoretically the scaling of several parameters of Rydberg excitons with n, for some of which we indeed find laws different from those of atoms. For others we find identical scaling laws with n, even though their origin may be distinctly different from the atomic case. At zero field the energy splitting of a particular multiplet n scales as n-3 due to crystal-specific terms in the Hamiltonian, e. g., from the valence band structure. From absorption spectra in magnetic field we find for the first crossing of levels with adjacent principal quantum numbers a Br. n-4 dependence of the resonance field strength, Br, due to the dominant paramagnetic term unlike for atoms for which the diamagnetic contribution is decisive, resulting in a Br. n-6 dependence. By contrast, the resonance electric field strength shows a scaling as Er. n-5 as for Rydberg atoms. Also similar to atoms with the exception of hydrogen we observe anticrossings between states belonging to multiplets with different principal quantum numbers at these resonances. The energy splittings at the avoided crossings scale roughly as n-4, again due to crystal specific features in the exciton Hamiltonian. The data also allow us to assess the susceptibility of Rydberg excitons to the external fields: The crossover field strength in magnetic field from a hydrogenlike exciton to a magnetoexciton dominated by electron and hole Landau level quantization scales as n-3. In electric field, on the other hand, we observe the exciton polarizability to scale as n7. At higher fields, the exciton ionization can be studied with ionization voltages that demonstrate an n-4 scaling law. Particularly interesting is the field dependence of the width of the absorption lines which remains constant before dissociation for high enough n, while for small n less than or similar to 12 an exponential increase is found. These results are in excellent agreement with theoretical predictions.

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