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Tianshu Jiang

Publications and source records attributed to Tianshu Jiang.

15 recordsLinked to original sources
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↗
arXiv2026

Parabolic Bogomolov--Gieseker Inequality and Pluriharmonic Metrics on Regular Parabolic Higgs Sheaves over Compact K\"ahler Manifolds

We prove a parabolic Bogomolov--Gieseker inequality for stable regular parabolic Higgs sheaves on a compact K\"ahler manifold \((X,\omega)\) equipped with a simple normal crossing divisor \(D\). We also prove that a polystable regular parabolic Higgs sheaf admits a pluriharmonic metric on \(X\setminus D\), provided that each stable summand has parabolic degree zero and vanishing integrated second parabolic Chern character.

math.DG↗
arXiv2026

Orbifold Uniformization of Complex Algebraic Variety via Polystable Parabolic Higgs Bundle

Let \(X\) be a smooth complex projective variety of dimension \(n\geq 2\), and let \(D=D^p+D^c\), \(D^c=\sum_i D_i^c\), be a simple normal crossing divisor. We regard \(D^p\) as the cusp divisor and the components \(D_i^c\) as compact orbifold divisors with standard weights \(\alpha_i=1-1/p_i\). Let \(\mathcal X=X[\sqrt[p_i]{D_i^c}]_i\) be the root stack along the compact components. We study the canonical parabolic Higgs bundle \(E_*=(\Omega_X^1(\log D^p)\oplus\mathcal O_X)_*\), whose compact weights are the \(\alpha_i\) on the conormal lines of \(D_i^c\), while the parabolic structure along \(D^p\) is trivial. Assume that \((E_*,\theta)\) is polystable with respect to some ample line bundle and that equality holds in the parabolic Bogomolov--Gieseker inequality. We prove that the trace-free adjoint Higgs bundle is flat. The associated principal \(\mathrm{PU}(n,1)\)-variation gives a faithful monodromy representation \(\rho:\pi_1^{\mathrm{orb}}(\mathcal X^o)\to\mathrm{PU}(n,1)\) and a period map to the complex ball \(\mathbb B^n\). The period map is unramified in the orbifold sense and identifies \((\mathcal X,D^p)\) with the canonical orbifold toroidal compactification \((\mathcal T_\Gamma,D_\Gamma^{\mathrm{tor}})\) of a finite-volume ball quotient, where \(\Gamma=\rho(\pi_1^{\mathrm{orb}}(\mathcal X^o))\) is a finite-volume lattice satisfying the regular log-root condition. We also formulate this standard-weight uniformization as an equivalence of categories: the compactified quotient construction and the monodromy construction define quasi-inverse functors between the regular log-root lattice category \(\mathsf{Lat}_n^{\mathrm{reg}}\) and the standard Bogomolov--Gieseker category \(\mathsf{BG}_n^{\mathrm{std}}\).

math.AG↗
arXiv2024

Observation of non-Hermitian boundary induced hybrid skin-topological effect excited by synthetic complex frequencies

The hybrid skin-topological effect (HSTE) has recently been proposed as a mechanism where topological edge states collapse into corner states under the influence of the non-Hermitian skin effect (NHSE). However, directly observing this effect is challenging due to the complex frequencies of eigenmodes. In this study, we experimentally observe HSTE corner states using synthetic complex frequency excitations in a transmission line network. We demonstrate that HSTE induces asymmetric transmission along a specific direction within the topological band gap. Besides HSTE, we identify corner states originating from non-chiral edge states, which are caused by the unbalanced effective onsite energy shifts at the boundaries of the network. Furthermore, our results suggest that whether the bulk interior is Hermitian or non-Hermitian is not a key factor for HSTE. Instead, the HSTE states can be realized and relocated simply by adjusting the non-Hermitian distribution at the boundaries. Our research has deepened the understanding of a range of issues regarding HSTE, paving the way for advancements in the design of non-Hermitian topological devices.

physics.optics↗
arXiv2024

Off-stoichiometry engineering of the electrical and optical properties of SrNbO$_3$ by oxide molecular beam epitaxy

The highly conducting and transparent inorganic perovskites SrBO$_3$ with V, Nb, Mo, and their mixtures at the B-site have recently attracted the attention of the oxide electronics community as novel alternative transparent conducting oxides. For different applications from solar cells to transparent electronics, it is desirable to tune the optical transmission window in the ultraviolet (UV), visible and infrared (IR) range. The conventional approach is substitutional design at the A- and/or B-site. Here, we suggest a method by engineering the off-stoichiometry of the perovskite, opening new pathways to broaden the range of applications without adding additional elements. For oxide molecular beam epitaxy grown SrNbO$_3$ on GdScO$_3$ substrates, we show that controlled Sr deficiency shifts the plasma edge from about 2 eV in the visible range into the near-infrared region, 1.37 eV (similar to stoichiometric SrVO$_3$). Here, epitaxial growth allows going beyond the limitations of phase stability set by thermodynamics. The suggested approach opens a new design toolbox by including controlled vacancy sites as quasi-substitutional virtual elements.

cond-mat.mtrl-sci↗
arXiv2024

Three-dimensional non-reciprocal transport in photonic topological heterostructure of arbitrary shape

Electromagnetic wave propagation in three-dimensional space typically suffers omnidirectional scattering when encountering obstacles. In this study, we employed Chern vectors to construct a topological heterostructure, where large-volume non-reciprocal topological transport in three-dimension is achieved. The shape of the cross-section in the heterostructure can be arbitrary designed, and we experimentally observed the distinctive cross-shaped field pattern transport, non-reciprocal energy harvesting, and most importantly, the remarkable ability of electromagnetic wave to traverse obstacles and abrupt structure changes without encountering reflections in 3D space.

physics.optics↗
arXiv2023

The Premartensite and Martensite in Fe50Rh50 System

Metallic/intermetalic materials with BCC structures hold an intrinsic instability due to phonon softening along [110] dirrection, causing BCC to lower-symmetry phases transformation when the BCC structures are thermally or mechanically stressed. Fe50Rh50 binary system is one of the exceptional BCC structures (ordered-B2) that has not been yet showing such transformation upon application of thermal stress, although mechanical deformation results in B2 to disordered FCC (gamma) and L10 phases transformation. Here, a comprehensive transmission electron microscopy (TEM) study is conducted on thermally-stressed samples of Fe50Rh50 aged at water and liquid nitrogen from 1150 degree C and 1250 degree C. The results show that, samples quenched from 1150 degree C into water and liquid nitrogen show presence of 1/4{110} and 1/2{110} satellite reflections, the latter of which is expected from phonon dispersion curves obtained by density functional theory calculation. Therefore, it is believed that Fe50Rh50 maintains the B2 structure that is in premartensite state. Once Fe50Rh50 is quenched from 1250 degree C into liquid nitrogen, formation of two short-range ordered tetragonal phases with various c/a ratios (~1.15 and 1.4) is observed in line with phases formed from mechanically deformed (30%) sample. According to our observations, an accurate atomistic shear model ({110}<1-10>) is presented that describes the martensitic transformation of B2 to these tetragonal phases. These findings offer implications useful for understanding of magnetic and physical characteristics of metallic/intermetallic materials.

cond-mat.mtrl-sci↗
arXiv2022

Edge and corner states in 2D non-Abelian topological insulators from an eigenvector frame rotation perspective

We propose the concept of 2D non-Abelian topological insulator which can explain the energy distributions of the edge states and corner states in systems with parity-time symmetry. From the viewpoint of non-Abelian band topology, we establish the constraints on the 2D Zak phase and polarization. We demonstrate that the corner states in some 2D systems can be explained as the boundary mode of the 1D edge states arising from the multi-band non-Abelian topology of the system. We also propose the use of off-diagonal Berry phase as complementary information to assist the prediction of edge states in non-Abelian topological insulators. Our work provides an alternative approach to study edge and corner modes and this idea can be extended to 3D systems.

cond-mat.mes-hall↗
arXiv2021

Disordered transmission-line networks with and without parity symmetry

Topological states are useful because they are robust against disorder and imperfection. In this study, we consider the effect of disorder and the breaking of parity symmetry on a topological network system in which the edge states are protected by Chern numbers. In the absence of periodicity, the local Chern number is adopted to characterize the topological features of the network. Our numerical results show that the local Chern number and the edge states are very robust against onsite disorder as long as the gap of the bulk state continuum remains open and survives even when the bulk band gap is closed. Breaking the parity symmetry can destroy the quantization of local Chern numbers, compromising the existence of edge modes. We observed non-integer local Chern number peaks that are non-zero inside the bulk bands but these non-zero non-integral local Chern numbers are not associated with the existence of robust edge states.

cond-mat.dis-nn↗
arXiv2021

Four-band non-Abelian topological insulator and its experimental realization

Very recently, increasing attention has been focused on non-Abelian topological charges, e.g. the quaternion group Q8. Different from Abelian topological band insulators, these systems involve multiple tangled bulk bandgaps and support non-trivial edge states that manifest the non-Abelian topological features. Furthermore, a system with even or odd number of bands will exhibit significant difference in non-Abelian topological classifications. Up to now, there is scant research investigating the even-band non-Abelian topological insulators. Here, we both theoretically explored and experimentally realized a four-band PT (inversion and time-reversal) symmetric system, where two new classes of topological charges as well as edge states are comprehensively studied. We illustrate their difference from four-dimensional rotation senses on the stereographically projected Clifford tori. We show the evolution of bulk topology by extending the 1D Hamiltonian onto a 2D plane and provide the accompanying edge state distributions following an analytical method. Our work presents an exhaustive study of four-band non-Abelian topological insulators and paves the way to other even band systems.

cond-mat.mes-hall↗
arXiv2020

Experimental observation of non-Abelian topological charges and bulk-edge correspondence

In the past decades, topological concepts have emerged to classify matter states beyond the Ginzburg-Landau symmetry breaking paradigm. The underlying global invariants are usually characterized by integers, such as Chern or winding numbers. Very recently, band topology characterized by non-Abelian topological charges has been proposed, which possess non-commutative and fruitful braiding structures with multiple (>1) bandgaps entangled together. Despite many potential exquisite applications including quantum computations, no experimental observation of non-Abelian topological charges has been reported. Here, we experimentally observe the non-Abelian topological charges in a PT (parity and time-reversal) symmetric system. More importantly, we propose non-Abelian bulk-edge correspondence, where edge states are found to be described by non-Abelian charges. Our work opens the door towards non-Abelian topological phase characterization and manipulation.

cond-mat.mes-hall↗
arXiv2018

Angular momentum-dependent topological transport and its experimental realization using a transmission line network

Novel classical wave phenomenon analogs of the quantum spin Hall effect are mostly based on the construction of pseudo-spins. Here we show that the non-trivial topology of a system can also be realized using orbital angular momentum through angular-momentum-orbital coupling. The idea is illustrated with a tight-binding model and experimentally demonstrated with a transmission line network. We show experimentally that even a very small network cluster exhibits one-way topological edge states, and their properties can be described in terms of local Chern numbers. Our work provides a new mechanism to realize counterparts of the quantum spin Hall effect in classical waves and may offer insights for other systems.

cond-mat.mes-hall↗
arXiv2018

Dynamically encircling an exceptional point in anti-PT-symmetric systems: asymmetric mode switching for symmetry-broken states

Dynamically encircling an exceptional point (EP) in parity-time (PT) symmetric systems shows an interesting chiral dynamics, leading to asymmetric mode switching in which the output modes are different when the encircling direction is reversed. Here we show that the dynamical encircling of an EP in anti-PT-symmetric systems can also result in chiral dynamics if the starting/end point lies in the PT-broken phase, in contrast to PT-symmetric systems where chiral dynamics emerges if the starting/end point lies in the PT-unbroken phase. For many applications, such as signal processing using waveguides, the asymmetric mode switching of symmetry-broken modes in anti-PT-symmetric systems is more useful since each eigenmode is localized in one waveguide only. We develop an analytic theory for anti-PT-symmetric chiral dynamics and perform experiments using three waveguides to demonstrate the asymmetric mode switching. The new wave-manipulation phenomena observable in anti-PT-symmetric systems may pave the way towards designing on-chip optical systems with novel functionalities.

physics.optics↗
arXiv2016

A Generic Minimal Discrete Model for Toroidal Moments and Its Experimental Realization

It is well known that a closed loop of magnetic dipoles can give rise to the rather elusive toroidal moment. However, artificial structures required to generate the necessary magnetic moments are typically optically large, complex to make and easily compromised by the kinetic inductance at high frequencies. Instead of using magnetic dipoles, we propose a minimal model based on just three aligned discrete electric dipoles in which the occurrence of resonant toroidal modes is guaranteed by symmetry. The advantage of this model is its simplicity and the same model supports toroidal moments from the microwave regime up to optical frequencies as exemplified by a three-antenna array and a system consisting of three nano-sized plasmonic particles. Both the microwave and high-frequency configurations exhibit non-radiating "anapoles". Experiments in the microwave regime confirm the theoretical predictions.

physics.optics↗