arXiv subjects

Xuelong Chen

Publications and source records attributed to Xuelong Chen.

3 recordsLinked to original sources

arXiv2026

Ubiquitous topological materials protected by hidden partial symmetries

Symmetries play a crucial role in protecting the topological phases of insulators, ensuring the robustness of their surface states against perturbations. Traditionally, these symmetries have to be obeyed by the system as a whole, which is a rather strong constraint. In this work, we demonstrate that topological effects can also be realized through a substantially weaker form of symmetry that we coin \emph{partial latent symmetries}. For these, invariance is required only at certain energy scales of an effective Hamiltonian, rather than for the object as a whole. Applying this idea, we construct weak-symmetry versions of the Su-Schrieffer-Heeger and Benalcazar-Bernevig-Hughes models. These weak-symmetry models behave in many aspects just like their conventional brethren---in particular, they host robust edge states---, though the corresponding topological invariants are only \emph{approximately} quantized. We conclude this work by experimentally realizing Hermitian and non-Hermitian versions of such approximate topological insulators and probe their edge states. Overall, given the ubiquity of symmetry in all areas of physics and engineering, we foresee our work to serve as a cornerstone for exploring how conventional, strong symmetry requirements can be replaced by weak-symmetry ones.

cond-mat.mes-hall↗

arXiv2026

Beyond geometric symmetry: Broadband linear relations in wave scattering

The design and control of wave scattering, that is, of the reflection and transmission parameters of a device, is of ubiquitous importance. These parameters generally change with varying frequency, though certain \emph{frequency-independent} linear relations may exist between them. Reciprocity and geometric symmetry (reflections, rotations, etc.) are classic and well-known examples that are present in many devices and significantly ease their design. In this work, we go beyond these and introduce a new class of relations that cannot be induced by reciprocity or geometric symmetry. Choosing networks of waveguides as our workhorse, we discuss the conditions and consequences of such novel behaviour and showcase suitable example setups. We further experimentally test our predictions using coaxial cables and find excellent agreement in the broad frequency range between 0 and 1 GHz. Our work not only deepens the theoretical understanding of waveguide network dynamics, but also opens new avenues for applications in broadband signal processing, quantum information, and integrated photonics.

physics.optics↗

arXiv2023

Latent Su-Schrieffer-Heeger models

The Su-Schrieffer-Heeger (SSH) chain is the reference model of a one-dimensional topological insulator. Its topological nature can be explained by the quantization of the Zak phase, due to reflection symmetry of the unit cell, or of the winding number, due to chiral symmetry. Here, we harness recent graph-theoretical results to construct families of setups whose unit cell features neither of these symmetries, but instead a so-called latent or hidden reflection symmetry. This causes the isospectral reduction -- akin to an effective Hamiltonian -- of the resulting lattice to have the form of an SSH model. As we show, these latent SSH models exhibit features such as multiple topological transitions and edge states, as well as a quantized Zak phase. Relying on a generally applicable discrete framework, we experimentally validate our findings using electric circuits.

cond-mat.mes-hall↗