  Metamaterials made of periodic arrangements of electric permittivity and
magnetic permeability and arrays of resonators can provide optic properties
unexperienced in conventional materials, such as negative refractive index
which can be used to achieve superlensing and cloaking. Developing new simpler
structures with richer electromagnetic (EM) properties and wider working
frequency bands is highly demanded for fast light-based information transfer
and information processing. In the present work, we propose theoretically that
a honeycomb-structured LC circuit with short-range textures in inductance can
generate a topological photonic state accompanied by inversion between p- and
d-orbital like EM modes carrying optic orbital angular momenta (OAM). We
realize experimentally the topological photonic state in planar microstrips, a
sandwich structure of bottom metallic substrate, middle dielectric film and top
metallic strips with hexagonal patterns in strip width, in microwave frequency.
Measuring accurately the amplitude and phase of EM fields, we demonstrate
explicitly that topological interfacial EM waves launched from a linearly
polarized dipole source propagate in opposite directions according to the sign
of OAM, with the relative weight of p- and d-orbital like EM modes tunable
precisely by sweeping the frequency in the topological band gap, which can
hardly be achieved in other photonic systems and condensed-matter systems.
Achieving the topological photonic state in a simple and easy fabricable
structure, the present work uncovers a new direction for generating and
manipulating EM modes with rich internal degrees of freedom, which can be
exploited for various applications.
