Classification of scalar and dyadic nonlocal optical response models

Area of Science:

• Nanophotonics and Plasmonics
• Condensed Matter Physics

Background:

• Nonlocal optical response is a key nanoscale effect in metals and doped semiconductors.
• Existing models simplify this response, often assuming localized interactions.

Purpose of the Study:

• To classify and compare scalar and tensorial nonlocal optical response models.
• To investigate how tensorial models align with phenomenological descriptions of nonlocal response.

Main Methods:

• Explicit calculation comparing tensorial models (hydrodynamic Drude, generalized nonlocal optical response) with phenomenological scalar models.
• Analysis of nonlocal response functions, including their values (negative, complex) and regularization of optical near fields.

Main Results:

• Tensorial models exhibit significant differences from simple smeared-out distributions, with response functions taking negative and complex values.
• Nonlocal response partially regularizes diverging optical near fields.
• The hydrodynamic Drude model shows only 1/3 nonlocal smearing, while transverse and scalar models show 2/3 and 3/3, respectively.
• Scalar and transverse models predict plasmonic resonances below the plasma frequency, unlike the hydrodynamic model.

Conclusions:

• Nonlocal optical response models differ substantially in their mathematical descriptions and physical implications.
• The degree of nonlocal smearing varies significantly across different models.
• Specific nonlocal models offer unique predictions for plasmonic behavior, including resonances below the plasma frequency.