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    Home > Biochemistry News > Biotechnology News > The team of Professor Changying Zhao from Shanghai Jiaotong University revealed the asymmetric evolution mechanism of phase singularities in spectral space, and proposed a new method for nonreciprocal thermal radiation control

    The team of Professor Changying Zhao from Shanghai Jiaotong University revealed the asymmetric evolution mechanism of phase singularities in spectral space, and proposed a new method for nonreciprocal thermal radiation control

    • Last Update: 2021-12-25
    • Source: Internet
    • Author: User
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    Recently, the team of Professor Changying Zhao from Shanghai Jiaotong University published a research paper "Evolution and nonreciprocity of loss-induced topological phase singularity pairs" in the international journal Physical Review Letters.
    The team studied the loss-induced spectral space topology under a nonreciprocal system.
    The asymmetric dynamic evolution of the phase singularity and its application in breaking Kirchhoff’s law of thermal radiation

    .
    The first author of the paper is PhD student Liu Mengqi, and the corresponding authors are Professor Zhao Changying and Professor Qiu Chengwei from the National University of Singapore

    .

    Kirchhoff’s law of thermal radiation states that the emissivity and absorptivity of a material under thermal equilibrium conditions are equal e(λ,θ)=α(λ,θ)
    .
    This law guides the design and development of almost all heat radiation devices at present

    .
    But in fact, thermal radiation devices designed based on this law have inherent energy loss.
    For example, for solar absorbers, how much energy the absorber absorbs from sunlight, the absorber itself will also radiate the same proportion of energy to the sun

    .
    Therefore, studying how to break this law is of great significance for further improving the theory of micro-nano heat radiation and designing new micro-nano energy devices

    .
    In theory, Kirchhoff’s law is rooted in the reciprocity of Maxwell’s equations.
    Research on how to break the balance of emission/absorption requires attention to how to break the symmetry of time reversal (such as the use of magnetic materials) to achieve non-reciprocal thermal emission

    .
    However, at present, domestic and foreign scholars' research on non-reciprocal heat radiation mostly relies on large external or internal magnetic field conditions, and it is difficult to completely break Kirchhoff's law in a wide angle range (|e-α|→1 )

    .

    Figure 1 (Left picture) The generation mechanism of topological phase singularities; (Right picture) The relationship between the asymmetric evolutionary regulation of topological phase singularities in spectral space and system radiation loss

    The research team used magneto-optical materials to systematically reveal material loss by studying the asymmetric characteristics of topological phase singularity pairs (TPSPs) split by bound states (BICs) in the continuum in the spectrum-parameter space.
    And radiation loss, the impact mechanism on the generation, evolution and annihilation of asymmetric TPSPs, and its high Q factor characteristics make it possible to observe strong non-reciprocity even under low external magnetic field conditions

    .
    In particular, different from the polarization singularities of vortex light in real space and momentum space, the phase singularities existing in the spectrum-parameter space induced by loss are discovered as a new class of topological features: phase diagrams in the spectrum-parameter space Above, an integer topological charge can be obtained around this point; when the system parameters are changed, these singularities will not suddenly disappear, only their position in the spectrum-parameter space will be changed

    .
    In addition, by controlling the system parameters, the research established the relationship between the number of BICs and the angular position under the non-reciprocal system, which ensures the active regulation of TPSPs for topology protection in a wide range of angles

    .

    Figure 2 Non-reciprocal thermal radiation control based on phase singularity of asymmetric topology

    This kind of singularity appears at the position where the reflection intensity is 0.
    According to the conservation of energy, it means that the absorptivity/emissivity at the singularity is 1

    .
    Therefore, the above-mentioned asymmetric phase singularity characteristics can be directly applied to the design of non-reciprocal heat radiation devices

    .
    Using asymmetric TPSPs, perfect non-reciprocal emission can be achieved at multiple angles, and absorption can be suppressed across the entire spectrum

    .
    The article also systematically compared the existing design methods of non-reciprocal heat radiation devices, and extended the related findings of TPSPs to the Weyl semi-metal system

    .

    This research applies asymmetric TPSPs to the design of non-reciprocal heat radiation devices, and provides a new method for theoretical and experimental research that breaks Kirchhoff's law
    .
    The combination of nonreciprocity and topological characteristics has produced some novel physical phenomena, and also provided new ideas for application research in micro-nano thermal radiation control, new thermal radiation energy device development, enhanced magneto-optical effect, and topological metasurface design.
    Ideas

    .

    The research work has been funded by key projects of the National Natural Science Foundation of China, key international cooperation projects, and key basic research projects of Shanghai
    .
    Professor Changying Zhao’s team has long been committed to the research of micro-nano-scale thermal radiation mechanism, experiment and application, especially in disordered media and metamaterial/metasurface radiation mechanism, near-field thermal radiation theory and experiment, coherent scattering, micro-nano heating Systematic in-depth research has been carried out in the design and development of radiation energy devices, and has been published in international journals such as Physical Review Letters, Advanced Materials, Nano Letters, Annual Review of Heat Transfer, ACS Photonics, Physical Review Applied, Physical Review B, IJHMT, etc.
    in recent years A series of research papers

    .

    Link to the paper : https://journals.
    aps.
    org/prl/abstract/10.
    1103/PhysRevLett.
    127.
    266101





    Institute of Engineering Thermophysics




    School of Mechanical and Power Engineering



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