arXiv subjects

Yejian Hu

Publications and source records attributed to Yejian Hu.

5 recordsLinked to original sources

arXiv2026

Implementing non-Abelian Hatano-Nelson model in electric circuits

Non-Hermitian systems generally host complex spectra that bring unique spectral topologies, leading to the spectral braiding and non-Hermitian skin effect. The experimental exploration of non-Hermitian physics is mainly concentrated in artificial systems due to the flexibility in the introduction of the non-Hermiticity, but to date has focused only on the systems without gauge fields or with Abelian gauge fields. Here, we propose a non-Abelian Hatano-Nelson model with a nonreciprocal U(2) gauge field. The gauge field induces two non-Hermitian phenomena: the first is the Hopf-link-shaped complex energy braiding, and the second is the bipolar skin effect arising under the non-Abelian condition. The non-Abelian Hatano-Nelson model is implemented in electric circuits, and the Hopf-link-shaped admittance spectra and bipolar skin admittance modes are observed. Our work enriches the experimental non-Hermitian physics, and provides an approach to designing multifunctional non-Hermitian devices.

quant-ph↗

arXiv2026

Observation of exceptional topology and nonlocal skin effect in Klein bottle electric circuits

Symmetry and its representation play a crucial role in topological phases, including both Hermitian and non-Hermitian paradigms. In the presence of synthetic gauge field, spatial symmetries should be projectively represented, which can modify the Brillouin manifold. However, this is often overlooked in non-Hermitian systems. Here, we present that momentum-space non-symmorphic reflection symmetry, a typical projective symmetry, induce exceptional topology and the nonlocal skin effect in a two-dimensional non-Hermitian electric circuit. We observe the total topological charges 2, rather than 0, for all exceptional points in a Brillouin Klein bottle manifold, and the phase transition when an exceptional point crosses the antiparallel boundary and flips its topological charge. We further observe a novel skin effect that the skin modes at one side are nonlocally connected to those on the opposite side separated by half of the reciprocal lattice. Our results unveil the unique non-Hermitian phenomena enabled by the projective symmetry, and open avenues for exploring the non-Hermitian topology beyond Brillouin torus manifold.

cond-mat.mes-hall↗

arXiv2025

Higher-order exceptional ring semimetal with real hinge states in phononic crystals

Non-Hermitian topological phase, with the novel concepts such as exceptional points and skin effect, has opened up a new paradigm beyond Hermitian topological physics. Exceptional ring semimetal, featured by a stable ring of exceptional points in three dimensions, exhibits first-order topological properties, including topological surface states and surface-dependent skin effect. Nevertheless, despite extensive research on Hermitian higher-order insulators and semimetals, higher-order exceptional ring semimetal is just emerging. Here, we report the first realization of a higher-order Weyl exceptional ring semimetal in a three-dimensional lossy phononic crystal. The non-Hermitian higher-order topology reflects in the topological hinge states and hinge-dependent skin effect. Counterintuitively, the topological hinge states maintain purely real energy even under a high loss level, ensuring robust hinge-state propagation. Our findings evidence the non-Hermitian higher-order bulk-boundary correspondence of exceptional ring semimetal, and may pave the way to non-Hermitian functional acoustic devices.

cond-mat.mes-hall↗

arXiv2024

Observation of exceptional line semimetal in three-dimensional non-Hermitian phononic crystals

Non-Hermitian topological phases, which exhibit unique features such as skin effect and exceptional points originated from nontrivial band topologies in complex plane, have attracted enormous attention in condensed-matter physics and metamaterials. Here we report the realization of an exceptional line semimetal in a three-dimensional non-Hermitian phononic crystal. A pair of exceptional rings with opposite topologies are connected by the drumhead bulk states in the first Brillouin zone. The exceptional rings not only possess wave-function topology and thus result in the drumhead surface states, but also host spectral topology and thereby give rise to the hybrid-order geometry-dependent skin effect in three dimensions. Our experimental results evidence the complete non-Hermitian bulk-boundary correspondence of the three-dimensional exceptional line semimetal, and may pave the way for designing non-Hermitian acoustic devices.

cond-mat.mes-hall↗

arXiv2022

Non-abelian gauge fields in circuit systems

Circuits can provide a platform to study novel physics and have been used, for example, to explore various topological phases. Gauge fields-particularly, non-Abelian gauge fields-can play a pivotal role in the design and modulation of novel physical states, but their circuit implementation has so far been limited. Here we show that non-Abelian gauge fields can be synthesized in circuits created from building blocks that consist of capacitors, inductors and resistors. With these building blocks, we create circuit designs for the spin-orbit interaction and the topological Chern state, which are phenomena that represent non-Abelian gauge fields in momentum space. We also use the approach to design non-reciprocal circuits that can be used to implement the non-Abelian Aharonov-Bohm effect in real space.

cond-mat.mes-hall↗