Ideal type-II Weyl points in topological circuits

TL;DR

This paper reports the experimental realization of ideal type-II Weyl points in topological circuits, demonstrating their unique tilted band structure and surface states, thus enabling advanced studies in Weyl physics.

Contribution

The authors create an ideal topological circuit system with four type-II Weyl points by stacking 2D LC resonator layers, a novel approach for studying Weyl physics.

Findings

Observation of four ideal type-II Weyl points

Demonstration of tilted band structure with same sign group velocities

Detection of topological surface states in an incomplete bandgap

Abstract

Weyl points (WPs), as nodal degenerate points in three-dimensional (3D) momentum space, are ideal if they are symmetry-related, well-separated, residing at the same energy and far from the nontopological bands. Although type-II WPs show some unique features compared with type-I counterparts, ideal type-II WPs have not yet been reported due to the lack of an ideal Weyl system with enough flexibility to tilt the dispersion bands. By stacking two-dimensional (2D) layers of inductor-capacitor (LC) resonator dimers with the breaking of parity inversion symmetry, here we experimentally realize the topological circuits with only the topological bands and observe a minimal number of four ideal type-II WPs. Two hallmark features of type-II WPs: a strongly tilted band structure with two group velocities having the same sign near type-II WPs and the topological surface states in an incomplete bandgap have been demonstrated. Our results establish an ideal system to the further study of Weyl physics and provide a new perspective to the access of topological matters.