-
Anyon-Induced Criticality and Dynamical Stability in Non-Hermitian Many-Body Systems
Authors:
Yi Qin,
Yee Sin Ang,
Linhu Li,
Ching Hua Lee
Abstract:
We show that anyonic statistics fundamentally reshapes non-Hermitian many-body physics by intrinsically breaking pseudo-Hermiticity, leading to a unique real-complex spectral transition with characteristically dense states in Im$E$. This anyon-induced transition occurs even when bosonic and pseudofermionic counterparts remain entirely real, revealing a form of non-Hermitian criticality driven pure…
▽ More
We show that anyonic statistics fundamentally reshapes non-Hermitian many-body physics by intrinsically breaking pseudo-Hermiticity, leading to a unique real-complex spectral transition with characteristically dense states in Im$E$. This anyon-induced transition occurs even when bosonic and pseudofermionic counterparts remain entirely real, revealing a form of non-Hermitian criticality driven purely by exchange statistics. The resulting spectrum exhibits enhanced gaps in Im$E$ that dynamically isolate dominant eigenstates, producing anomalously stable short-time quench dynamics for anyons. Our results identify anyonic statistics as an intrinsic mechanism for generating unconventional non-Hermitian critical behavior usually associated with highly non-local systems.
△ Less
Submitted 18 March, 2026;
originally announced March 2026.
-
Generalized Brillouin Zone Fragmentation
Authors:
Haiyu Meng,
Yee Sin Ang,
Ching Hua Lee
Abstract:
The Generalized Brillouin Zone (GBZ) encodes how lattice momentum is complex-deformed due to non-Hermitian skin accumulation, and has proved essential in restoring bulk-boundary correspondences. However, we find that generically, the GBZ is neither unique nor well-defined if more than one skin localization direction or strength exists, even in systems with no asymmetric hoppings. Instead, open bou…
▽ More
The Generalized Brillouin Zone (GBZ) encodes how lattice momentum is complex-deformed due to non-Hermitian skin accumulation, and has proved essential in restoring bulk-boundary correspondences. However, we find that generically, the GBZ is neither unique nor well-defined if more than one skin localization direction or strength exists, even in systems with no asymmetric hoppings. Instead, open boundary condition (OBC) eigenstates become complicated superpositions of multiple competing skin modes from "fragments" of all possible GBZs solutions. We develop a formalism that computes the fragmented GBZ in a scalable manner, with fragmentation extent quantified through our newly-defined composition IPR and spectral relative entropy. GBZ fragmentation is revealed to fundamentally challenge the notion of discontinuous phase transitions, since topological winding contributions from different GBZ fragments can "melt away" at different rates. Phenomenologically, GBZ fragmentation also leads to edge localization in all observables in energetically weighted ensembles such as thermal ensembles. This contrasts with conventional GBZs where the skin localization completely cancels in biorthogonal expectations. Occurring universally in multi-mode non-Hermitian media, as we concretely demonstrate with photonic crystal simulations, GBZ fragmentation points towards a new paradigm that is essential for understanding the band structure and the topological and dynamical properties of diverse generic non-Hermitian systems.
△ Less
Submitted 15 February, 2026; v1 submitted 18 August, 2025;
originally announced August 2025.
-
Many-body critical non-Hermitian skin effect
Authors:
Yi Qin,
Yee Sin Ang,
Ching Hua Lee,
Linhu Li
Abstract:
Criticality in non-Hermitian systems unveils unique phase transitions and scaling behaviors beyond Hermitian paradigms, offering new insights into the interplay between gain/loss, non-reciprocity, and complex energy spectra. In this paper, we uncover a new class of many-body critical non-Hermitian skin effect (CSE) originating from the interplay between multiple non-Hermitian pumping channels and…
▽ More
Criticality in non-Hermitian systems unveils unique phase transitions and scaling behaviors beyond Hermitian paradigms, offering new insights into the interplay between gain/loss, non-reciprocity, and complex energy spectra. In this paper, we uncover a new class of many-body critical non-Hermitian skin effect (CSE) originating from the interplay between multiple non-Hermitian pumping channels and Hubbard interactions. In particular, criticality in the real-to-complex transitions can selectively emerge within the subspace of bound states or scattering states, as well as their interacting admixtures. These mechanisms possess no single-particle analog and can be diagnosed through a specially defined correlation function. As more particles are involved, higher-order CSEs naturally arise, with greatly enhanced effective coupling strengths and hence greater experimental accessibility. Our results reveal an enriched landscape of non-Hermitian critical phenomena in interacting many-body systems, and pave the way for investigating unconventional non-Hermitian criticality in the context of various interaction-induced particle clustering configurations.
△ Less
Submitted 2 June, 2025;
originally announced June 2025.
-
Strongly correlated multi-electron bunches from interaction with quantum light
Authors:
Suraj Kumar,
Jeremy Lim,
Nicholas Rivera,
Wesley Wong,
Yee Sin Ang,
Lay Kee Ang,
Liang Jie Wong
Abstract:
Strongly correlated electron systems are a cornerstone of modern physics, being responsible for groundbreaking phenomena from superconducting magnets to quantum computing. In most cases, correlations in electrons arise exclusively due to Coulomb interactions. In this work, we reveal that free electrons interacting simultaneously with a light field can become highly correlated via mechanisms beyond…
▽ More
Strongly correlated electron systems are a cornerstone of modern physics, being responsible for groundbreaking phenomena from superconducting magnets to quantum computing. In most cases, correlations in electrons arise exclusively due to Coulomb interactions. In this work, we reveal that free electrons interacting simultaneously with a light field can become highly correlated via mechanisms beyond Coulomb interactions. In the case of two electrons, the resulting Pearson correlation coefficient (PCC) for the joint probability distribution of the output electron energies is enhanced over 13 orders of magnitude compared to that of electrons interacting with the light field in succession (one after another). These highly correlated electrons are the result of momentum and energy exchange between the participating electrons via the external quantum light field. Our findings pave the way to the creation and control of highly correlated free electrons for applications including quantum information and ultra-fast imaging.
△ Less
Submitted 13 May, 2024; v1 submitted 23 April, 2024;
originally announced April 2024.
-
Exceptional points in non-Hermitian Photonics: Applications and Recent Developments
Authors:
Haiyu Meng,
Yee Sin Ang,
Ching Hua Lee
Abstract:
Exceptional points are complex branching singularities of non-Hermitian bands that have lately attracted considerable interest, particularly in non-Hermitian photonics. In this article, we review some recent developments in non-Hermitian photonic platforms such as waveguides, photonic crystals, Fabry-Perot resonators and plasmonic systems, and suggest how optical non-linearities and exceptional bo…
▽ More
Exceptional points are complex branching singularities of non-Hermitian bands that have lately attracted considerable interest, particularly in non-Hermitian photonics. In this article, we review some recent developments in non-Hermitian photonic platforms such as waveguides, photonic crystals, Fabry-Perot resonators and plasmonic systems, and suggest how optical non-linearities and exceptional bound states can significantly impact the development of non-Hermitian photonics in the near future.
△ Less
Submitted 27 October, 2023; v1 submitted 25 October, 2023;
originally announced October 2023.
-
Experimental observation of exceptional bound states in a classical circuit network
Authors:
Deyuan Zou,
Tian Chen,
Haiyu Meng,
Yee Sin Ang,
Xiangdong Zhang,
Ching Hua Lee
Abstract:
Exceptional bound (EB) states represent an unique new class of robust bound states protected by the defectiveness of non-Hermitian exceptional points. Conceptually distinct from the more well-known topological states and non-Hermitian skin states, they were recently discovered as a novel source of negative entanglement entropy in the quantum entanglement context. Yet, EB states have been physicall…
▽ More
Exceptional bound (EB) states represent an unique new class of robust bound states protected by the defectiveness of non-Hermitian exceptional points. Conceptually distinct from the more well-known topological states and non-Hermitian skin states, they were recently discovered as a novel source of negative entanglement entropy in the quantum entanglement context. Yet, EB states have been physically elusive, being originally interpreted as negative probability eigenstates of the propagator of non-Hermitian Fermi gases. In this work, we show that EB states are in fact far more ubiquitous, also arising robustly in broad classes of systems whether classical or quantum. This hinges crucially on a newly-discovered spectral flow that rigorously justifies the EB nature of small candidate lattice systems. As a highlight, we present their first experimental realization through an electrical circuit, where they manifest as prominent stable resonant voltage profiles. Our work brings a hitherto elusive but fundamentally distinctive quantum phenomenon into the realm of classical metamaterials, and provides a novel pathway for the engineering of robust modes in otherwise sensitive systems.
△ Less
Submitted 3 August, 2023;
originally announced August 2023.
-
Quantum interference between fundamentally different processes is enabled by shaped input wavefunctions
Authors:
J. Lim,
Y. S. Ang,
L. K. Ang,
L. J. Wong
Abstract:
We present a general framework for quantum interference (QI) between multiple, fundamentally different processes. Our framework reveals the importance of shaped input wavefunctions in enabling QI, and predicts unprecedented interactions between free electrons, bound electrons, and photons: (i) the vanishing of the zero-loss peak by destructive QI when a shaped electron wavepacket couples to light,…
▽ More
We present a general framework for quantum interference (QI) between multiple, fundamentally different processes. Our framework reveals the importance of shaped input wavefunctions in enabling QI, and predicts unprecedented interactions between free electrons, bound electrons, and photons: (i) the vanishing of the zero-loss peak by destructive QI when a shaped electron wavepacket couples to light, under conditions where the electron's zero-loss peak otherwise dominates; (ii) QI between free electron and atomic (bound electron) spontaneous emission processes, which can be significant even when the free electron and atom are far apart, breaking the common notion that electron and atom must be close by to significantly affect each other's processes. Our work shows that emerging quantum waveshaping techniques unlock the door to greater versatility in light-matter interactions and other quantum processes in general.
△ Less
Submitted 10 August, 2022; v1 submitted 26 November, 2021;
originally announced November 2021.
-
Universal model for electron thermal-field emission from two-dimensional semimetals
Authors:
L. K. Ang,
Yee Sin Ang,
Ching Hua Lee
Abstract:
We present the theory of out-of-plane (or vertical) electron thermal-field emission from 2D semimetals. We show that the current-voltage-temperature characteristic is well-captured by a universal scaling relation applicable for broad classes of 2D semimetals, including graphene and its few-layer, nodal point semimetal, Dirac semimetal at the verge of topological phase transition and nodal line sem…
▽ More
We present the theory of out-of-plane (or vertical) electron thermal-field emission from 2D semimetals. We show that the current-voltage-temperature characteristic is well-captured by a universal scaling relation applicable for broad classes of 2D semimetals, including graphene and its few-layer, nodal point semimetal, Dirac semimetal at the verge of topological phase transition and nodal line semimetal. Here an important consequence of the universal emission behavior is revealed: in contrast to the common expectation that band topology shall manifest differently in the physical observables, band topologies in two spatial dimension are indistinguishable from each others and bear no special signature in the electron emission characteristics. Our findings represent the quantum extension of the universal semiclassical thermionic emission scaling law in 2D materials, and provide the theoretical foundations for the understanding of electron emission from cathode and charge interface transport for the design of 2D-material-based vacuum nanoelectronics.
△ Less
Submitted 17 April, 2023; v1 submitted 31 March, 2020;
originally announced March 2020.
-
Relativistic space-charge-limited current for massive Dirac fermions
Authors:
Y. S. Ang,
M. Zubair,
L. K. Ang
Abstract:
A theory of relativistic space-charge-limited current (SCLC) is formulated to determine the SCLC scaling, $J\propto V^α/L^β$, for a finite bandgap Dirac material of length $L$ biased under a voltage $V$. In a one-dimensional (1D) bulk geometry, our model allows ($α$, $β$) to vary from (2,3) for the non-relativistic model in traditional solids to (3/2,2) for the ultra-relativistic model of massless…
▽ More
A theory of relativistic space-charge-limited current (SCLC) is formulated to determine the SCLC scaling, $J\propto V^α/L^β$, for a finite bandgap Dirac material of length $L$ biased under a voltage $V$. In a one-dimensional (1D) bulk geometry, our model allows ($α$, $β$) to vary from (2,3) for the non-relativistic model in traditional solids to (3/2,2) for the ultra-relativistic model of massless Dirac fermions. For a two-dimensional (2D) thin-film geometry, we obtain $α= β$ that varies between 2 and 3/2, respectively, at the non-relativistic and ultra-relativistic limits. We further provide a rigorous proof based on a Green's function approach that for uniform SCLC model described by carrier density-dependent mobility, the scaling relations of the 1D bulk model can be directly mapped into the case of 2D thin film for any contact geometries. Our simplified approach provides a convenient tool to obtain the 2D thin-film SCLC scaling relations without the need of explicitly solving the complicated 2D problems. Finally, this work clarifies the inconsistency in using the traditional SCLC models to explain the experimental measurement of 2D Dirac semiconductor. We conclude that the voltage-scaling $3/2 < α< 2$ is a distinct signature of massive Dirac fermions in Dirac semiconductor and is in agreement with experimental SCLC measurement in MoS$_2$.
△ Less
Submitted 16 March, 2017;
originally announced March 2017.