We study a system tuned to an absorbing exceptional point and explore its use to efficiently receive and store an incoming wave with an envelope different from the absorbing-eigenmode envelope. Specifically, while abs...
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We study a system tuned to an absorbing exceptional point and explore its use to efficiently receive and store an incoming wave with an envelope different from the absorbing-eigenmode envelope. Specifically, while absorbing states of lossless resonators have an exponentially increasing envelope, we focus on capturing naturally emitted waves with an exponentially decreasing envelope. We find that, when tuning a cavity to an nth-order absorbing exceptional point (EP), n+1 temporal orders of any incoming waveform can be perfectly captured, leading to significantly less scattering and increasing the overall absorption efficiency for general waveforms. We present an approach to tune a cavity to an EP and demonstrate less scattering by an order of magnitude for a decaying incoming waveform. Our results may be used for efficient passive state transfer and detection of spontaneous emission.
The quantum spin Hall states are usually expected to possess gapless, helical edge modes. We show that the generic, n-fold-symmetric, momentum planes of three-dimensional, stable Dirac semimetals, which are orthogonal...
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The quantum spin Hall states are usually expected to possess gapless, helical edge modes. We show that the generic, n-fold-symmetric, momentum planes of three-dimensional, stable Dirac semimetals, which are orthogonal to the direction of nodal separation are examples of generalized quantum spin Hall systems, that possess quantized, spin or relative Chern numbers as bulk topological invariants, and gapped edge modes. We demonstrate these planes and the celebrated Bernevig-Zhang-Hughes model support identical quantized, non-Abelian Berry flux of magnitude 2π. Hence, they display identical quantized, topological response such as spin-charge separation and pumping of one Kramers-pair or SU(2) doublet, when probed with a magnetic flux tube. The Dirac points are identified as unit-strength, monopoles of SO(5) Berry connection, describing topological phase transitions between generalized quantum spin Hall and trivial insulators. Our work identifies precise bulk invariant and quantized response of Dirac semimetals, which are not diagnosed by nested Wilson loops and filling anomaly of corner-localized-states, and shows that many two-dimensional higher-order topological insulators can be understood as generalized quantum spin Hall systems.
Combinatorial optimization problems are ubiquitous in various disciplines and applications. Many heuristic algorithms have been devoted to solve these types of problems. In order to increase the efficiency for finding...
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One of the central goals of neuroscience is to gain a mechanistic understanding of how the dynamics of neural circuits give rise to their observed function. A popular approach towards this end is to train recurrent ne...
Magnetotransport measurements of the centrosymmetric square net Eu(Ga1−xAlx)4 compounds reveal evidence of both reciprocal- and real-space topology. For compositions 0.50≤x≤0.90, several intermediate field phases ar...
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Magnetotransport measurements of the centrosymmetric square net Eu(Ga1−xAlx)4 compounds reveal evidence of both reciprocal- and real-space topology. For compositions 0.50≤x≤0.90, several intermediate field phases are found by magnetization measurements when H∥c, where a maximum in the topological Hall effect is observed, pointing to the existence of topological (real-space topology) or noncoplanar spin textures. For 0.25≤x≤0.39, magnetization measurements reveal an intermediate field state, but no transition is visible in the Hall measurements. For x=0.15, only one magnetic transition occurs below the Néel temperature TN, and no intermediate field spin reorientations are observed. The Hall effect varies smoothly before the spin-polarized (SP) state. However, in the SP state, Hall measurements reveal a large anomalous Hall effect (AHE) for all compositions, a consequence of reciprocal-space topology. Density functional theory calculations in the paramagnetic state indeed reveal a Dirac point that lies very near the Fermi energy, which is expected to split into Weyl nodes in the SP state, thereby explaining the observed AHE. These results suggest the Eu(Ga1−xAlx)4 family is a rare material platform where real- and reciprocal-space topology exist in a single material platform.
The synergy between topology and non-Hermiticity in photonics holds potential for optical devices that are robust against defects. We demonstrate a non-Hermitian plasmonic-dielectric metasurface in the visible with no...
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The identification of distinct charge transport features, deriving from nontrivial bulk band and surface states, has been a challenging subject in the field of topological systems. In topological Dirac and Weyl semime...
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The identification of distinct charge transport features, deriving from nontrivial bulk band and surface states, has been a challenging subject in the field of topological systems. In topological Dirac and Weyl semimetals, nontrivial conical bands with Fermi-arc surface states give rise to negative longitudinal magnetoresistance due to chiral anomaly effect and unusual thickness dependent quantum oscillation from Weyl-orbit effect, which were demonstrated recently in experiments. In this work, we report the experimental observations of large nonlinear and nonreciprocal transport effects for both longitudinal and transverse channels in an untwinned Weyl metal of SrRuO3 thin film grown on a SrTiO3 substrate. From rigorous measurements with bias current applied along various directions with respect to the crystalline principal axes, the magnitude of nonlinear Hall signals from the transverse channel exhibits a simple sinα dependence at low temperatures, where α is the angle between bias current direction and orthorhombic [001]o, reaching a maximum when current is along orthorhombic [11¯0]o. On the contrary, the magnitude of nonlinear and nonreciprocal signals in the longitudinal channel attains a maximum for bias current along [001]o, and it vanishes for bias current along [11¯0]o. The observed α-dependent nonlinear and nonreciprocal signals in longitudinal and transverse channels reveal a magnetic Weyl phase with an effective Berry curvature dipole along [11¯0]o from surface states, accompanied by 1D chiral edge modes along [001]o.
Magnetotransport measurements on the centrosymetric square-net Eu(Ga1−xAlx)4 compounds reveal evidence for both reciprocal- and real-space topology. For compositions 0.50 ≤ x ≤ 0.90, several intermediate field phase...
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