scholarly journals Non-Hermitian Weyl Semimetals: Non-Hermitian Skin Effect and non-Bloch Bulk-Boundary Correspondence

2021 ◽  
Author(s):  
Xiaosen Yang ◽  
Yang Cao ◽  
Yunjia Zhai
Keyword(s):  
Skin Effect ◽  
Boundary Correspondence ◽  
Weyl Semimetals

Novel topological end modes and breaking of bulk boundary correspondence in skin-effect absent superconductive chain

2021 ◽  
Author(s):  
Huan-Yu Wang ◽  
Wu-Ming Liu
Keyword(s):  
Skin Effect ◽  
Open Quantum Systems ◽  
Quantum Systems ◽  
Topological Invariants ◽  
Quantum Matter ◽  
Topological Quantum ◽  
Boundary Correspondence ◽  
Quantum Chain ◽  
New Type ◽  
Majorana Modes

Abstract Topological nontrivial systems feature isolated gapless edge modes, and play a key role in advancing our understanding of quantum matter. A most profound way to characterize edge modes above is through bulk topological invariants, which is known as bulk boundary correspondence. Recent studies on non-Hermitian physics have pronounced the broken bulk-boundary correspondence with the presence of skin effect. Here, we propose a new type of fermionic topological edge modes η, satisfying η+= iη,η2=-i. Remarkably, we demonstrate that for both two cases: superconductive chain with purely η modes and quantum chain with η, Majorana modes γ on different ends, fermion parity can be well defined. Interestingly, for the latter case, broken bulk boundary correspondence is observed despite the absence of skin effects . The phenomenon above is unique to open quantum systems. For the junction with both η,γ modes, the current will not remain sinusoid form but decay exponentially. The exchange of η modes obeys the rules of non-abelian statistics, and can find its applications in topological quantum computing.

scholarly journals Non-Hermitian Skin Effect in a Non-Hermitian Electrical Circuit

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Shuo Liu ◽  
Ruiwen Shao ◽  
Shaojie Ma ◽  
Lei Zhang ◽  
Oubo You ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Periodic Boundary Condition ◽  
Periodic Boundary ◽  
Skin Effect ◽  
Open Circuit ◽  
Electrical Circuit ◽  
Finite System ◽  
Open Boundary ◽  
Edge States ◽  
Boundary Correspondence

The conventional bulk-boundary correspondence directly connects the number of topological edge states in a finite system with the topological invariant in the bulk band structure with periodic boundary condition (PBC). However, recent studies show that this principle fails in certain non-Hermitian systems with broken reciprocity, which stems from the non-Hermitian skin effect (NHSE) in the finite system where most of the eigenstates decay exponentially from the system boundary. In this work, we experimentally demonstrate a 1D non-Hermitian topological circuit with broken reciprocity by utilizing the unidirectional coupling feature of the voltage follower module. The topological edge state is observed at the boundary of an open circuit through an impedance spectra measurement between adjacent circuit nodes. We confirm the inapplicability of the conventional bulk-boundary correspondence by comparing the circuit Laplacian between the periodic boundary condition (PBC) and open boundary condition (OBC). Instead, a recently proposed non-Bloch bulk-boundary condition based on a non-Bloch winding number faithfully predicts the number of topological edge states.

scholarly journals Photonic non-Hermitian skin effect and non-Bloch bulk-boundary correspondence

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Xueyi Zhu ◽  
Huaiqiang Wang ◽  
Samit Kumar Gupta ◽  
Haijun Zhang ◽  
Biye Xie ◽  
...  
Keyword(s):  
Skin Effect ◽  
Boundary Correspondence

scholarly journals Defective edge states and anomalous bulk-boundary correspondence for topological insulators under non-Hermitian similarity transformation

2020 ◽  
Vol 34 (09) ◽  
pp. 2050146
Author(s):  
C. Wang ◽  
X.-R. Wang ◽  
C.-X. Guo ◽  
S.-P. Kou
Keyword(s):  
Chiral Symmetry ◽  
Topological Insulators ◽  
Skin Effect ◽  
Similarity Transformation ◽  
Topological Invariant ◽  
Inversion Symmetry ◽  
Edge States ◽  
Boundary Correspondence ◽  
Zhang Model ◽  
Symmetry Protected

It was known that for non-Hermitian topological systems due to the non-Hermitian skin effect, the bulk-edge correspondence is broken down. In this paper, by using one-dimensional Su–Schrieffer–Heeger model and two-dimensional (deformed) Qi–Wu–Zhang model as examples, the focus is on a special type of non-Hermitian topological system without non-Hermitian skin effect — topological systems under non-Hermitian similarity transformation. In these non-Hermitian systems, the defective edge states and the breakdown of bulk-edge correspondence are discovered. To characterize the topological properties, a new type of inversion symmetry-protected topological invariant — total [Formula: see text] topological invariant — has been introduced. In topological phases, defective edge states appear. With the help of the effective edge Hamiltonian, it was found that the defective edge states are protected by (generalized) chiral symmetry and thus the (singular) defective edge states are unstable against the perturbation breaking the chiral symmetry. In addition, the results are generalized to non-Hermitian topological insulators with inversion symmetry in higher dimensions. This work could help people to understand the defective edge states and the breakdown of bulk-edge correspondence for non-Hermitian topological systems.

scholarly journals Universal non-Hermitian skin effect in two and higher dimensions

2021 ◽  
Author(s):  
Kai Zhang ◽  
Zhensen Yang ◽  
Chen Fang
Keyword(s):  
Skin Effect ◽  
Physical Phenomenon ◽  
Higher Dimensions ◽  
Three Dimensions ◽  
One Dimension ◽  
Finite Area ◽  
Open Chain ◽  
Kondo Insulators ◽  
Boundary Spectrum ◽  
Weyl Semimetals

Abstract Skin effect, experimentally discovered in one dimension, describes the physical phenomenon that on an open chain, an extensive number of eigenstates of a non-Hermitian hamiltonian are localized at the end(s) of the chain. Here in two and higher dimensions, we establish a theorem that the skin effect exists, if and only if periodic-boundary spectrum of the hamiltonian covers a finite area on the complex plane. This theorem establishes the universality of the effect, because the above condition is satisfied in almost every generic non-Hermitian hamiltonian, and, unlike in one dimension, is compatible with all spatial symmetries. We propose two new types of skin effect in two and higher dimensions: the corner-skin effect where all eigenstates are localized at one corner of the system, and the geometry-dependent-skin effect where skin modes disappear for systems of a particular shape, but appear on generic polygons. An immediate corollary of our theorem is that any non-Hermitian system having exceptional points (lines) in two (three) dimensions exhibits skin effect, making this phenomenon accessible to experiments in photonic crystals, Weyl semimetals, and Kondo insulators.

scholarly journals The topological counterparts of non-Hermitian SSH models

2021 ◽  
Author(s):  
Yanzhen Han ◽  
J. S. Liu ◽  
Cheng-Shi Liu
Keyword(s):  
Magnetic Flux ◽  
Skin Effect ◽  
Analytical Form ◽  
Topological Invariants ◽  
Similarity Transformations ◽  
Boundary Correspondence ◽  
Bohm Effect ◽  
A Chain ◽  
Aharonov Bohm ◽  
Ssh Model

Abstract Inspired by the relevance between the asymmetric coupling amplitude and the imaginary gauge field, we construct the counterpart of the non-Hermitian SSH model. The idea is the nonzero imaginary magnetic flux vanishing when the boundary condition changes from periodic to open. The zero imaginary magnetic flux of the counterpart leads to the eliminating of the non-Hermitian skin effect and the non-Hermitian Aharonov-Bohm effect which ensures the recovery of the conventional bulk-boundary correspondence from the non-Bloch bulk-boundary correspondence. We explain how some the non-Hermitian models can be transformed to the non-Hermitian SSH models and how the non-reciprocal hopping in the non-Hermitian SSH models can be transformed from one term to the other terms by the similarity transformations. We elaborate why the effective imaginary magnetic flux disappears due to the interplay of the non-reciprocal hoppings in the partner of the non-Hermitian SSH model. As the results, we obtain the topological invariants of the non-Hermitian SSH model in analytical form defined in conventional Brillouin zone. The non-Hermitian SSH model in domain configuration on a chain is discussed with this method. The technique gives an alternative way to study the topological properties of non-Hermitian systems.

scholarly journals Topological properties of non-Hermitian Creutz Ladders

2021 ◽  
Author(s):  
Hui-Qiang Liang ◽  
Linhu Li
Keyword(s):  
Periodic Boundary Condition ◽  
Periodic Boundary ◽  
Skin Effect ◽  
Energy Gap ◽  
Dimensional Space ◽  
Two Dimensional ◽  
Topological Properties ◽  
One Dimensional ◽  
Boundary Correspondence ◽  
The One

Abstract In this work we study topological properties of the one-dimensional Creutz ladder model with different non-Hermitian asymmetric hoppings and on-site imaginary potentials, and obtain phase diagrams regarding the presence and absence of an energy gap and in-gap edge modes. The non-Hermitian skin effect (NHSE), which is known to break the bulk-boundary correspondence (BBC), emerges in the system only when the non-Hermiticity induces certain unbalanced non-reciprocity along the ladder. The topological properties of the model are found to be more sophisticated than that of its Hermitian counterpart, whether with or without the NHSE. In one scenario without the NHSE, the topological winding is found to exist in a two-dimensional plane embedded in a four-dimensional space of the complex Hamiltonian vector. The NHSE itself also possesses some unusual behaviors in this system, including a high spectral winding without the presence of long-range hoppings, and a competition between two types of the NHSE, with the same and opposite inverse localization lengths for the two bands, respectively. Furthermore, it is found that the NHSE in this model does not always break the conventional BBC, which is also associated with whether the band gap closes at exceptional points under the periodic boundary condition.

TREATMENT OF WELDED JOINTS BY A PULSE ELECTROMAGNETIC FIELD WITH SMALL SKIN-EFFECT

2018 ◽  
Vol 2018 (50) ◽  
pp. 106-114
Author(s):  
Yu. Vasetskiy ◽  
◽  
I. Kondratenko ◽  
I. Mazurenko ◽  
М. Pashchyn ◽  
...  
Keyword(s):  
Electromagnetic Field ◽  
Welded Joints ◽  
Skin Effect ◽  
Pulse Electromagnetic Field

Influence of fasteners and connections flexibility on deflections of steel building including the stressed skin effect

2018 ◽  
Vol 2 (21) ◽  
pp. 131-148 ◽  
Author(s):  
Natalia Korcz ◽  
Elżbieta Urbańska-Galewska
Keyword(s):  
Finite Elements ◽  
Skin Effect ◽  
Numerical Models ◽  
Orthotropic Shell ◽  
3D Structure ◽  
Negligible Effect ◽  
Transverse Stiffness ◽  
Shell Models ◽  
Steel Building ◽  
Two Sides

The paper presents the analysis of the influence of fasteners and connections flexibility on displacements of symmetrical single-bay pitched-roof steel building, including trapezoidal cladding acting as a diaphragm. The purpose of the article was to compare numerical models with and without taking into consideration fasteners and connections flexibility in order to observe the differences in transverse stiffness of the building during modifying model from the simple one to more complex and precise. The analyses were carried out for the 3D structure. Fasteners and connections were substituted by equivalent beam finite elements. Corrugated sheets were replaced by three types of equivalent orthotropic shell models and the influence of the choice of the model on the stiffness of the building was observed. The results showed that in the analysed structure the flexibility of fasteners and connections has negligible effect on transverse displacements of the building in the case of four sides fastening of the sheeting, however in the case of two sides fastening the influence significantly increases.

WELL TESTING HORIZONTALGAS-CONDENSATE WELLS

2017 ◽  
pp. 56-61
Author(s):  
M. L. Karnaukhov ◽  
O. N. Pavelyeva
Keyword(s):  
Comparative Analysis ◽  
Skin Effect ◽  
Horizontal Wells ◽  
Gas Condensate ◽  
Low Permeability ◽  
Well Testing ◽  
Flow Capacity ◽  
Formation Zone ◽  
Horizontal Wellbore

The well testing of gas-condensate horizontal wells are discussed in the article and the comparative analysis of borehole flow capacity, depending on the mode of it’s operation is presented. Extra attention is focused on the issue of timely identification of the reasons for the reduction of fluid withdrawal from the reservoir. The presence of high skin effect is proved, which confirms the existence of low-permeability of bottomhole formation zone related to condensation in the immediate area of the horizontal wellbore.

Sign in / Sign up

Export Citation Format

Share Document