Content of SPECIAL TOPIC—Phononics and phonon engineering in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Impact of counter-rotating-wave term on quantum heat transfer and phonon statistics in nonequilibrium qubit-phonon hybrid system Chen Wang(王晨), Lu-Qin Wang(王鲁钦), and Jie Ren(任捷) Chin. Phys. B, 2021, 30 (3): 030506.   DOI: 10.1088/1674-1056/abcfa8 Abstract （451）   HTML （7）    PDF （4726KB）（163）       Knowledge map    Counter-rotating-wave terms (CRWTs) are traditionally viewed to be crucial in open small quantum systems with strong system-bath dissipation. Here by exemplifying in a nonequilibrium qubit-phonon hybrid model, we show that CRWTs can play the significant role in quantum heat transfer even with weak system-bath dissipation. By using extended coherent phonon states, we obtain the quantum master equation with heat exchange rates contributed by rotating-wave-terms (RWTs) and CRWTs, respectively. We find that including only RWTs, the steady state heat current and current fluctuations will be significantly suppressed at large temperature bias, whereas they are strongly enhanced by considering CRWTs in addition. Furthermore, for the phonon statistics, the average phonon number and two-phonon correlation are nearly insensitive to strong qubit-phonon hybridization with only RWTs, whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition. Therefore, CRWTs in quantum heat transfer system should be treated carefully. Select First-principles analysis of phonon thermal transport properties of two-dimensional WS2/WSe2 heterostructures Zheng Chang(常征), Kunpeng Yuan(苑昆鹏), Zhehao Sun(孙哲浩), Xiaoliang Zhang(张晓亮), Yufei Gao(高宇飞), Xiaojing Gong(弓晓晶), and Dawei Tang(唐大伟) Chin. Phys. B, 2021, 30 (3): 034401.   DOI: 10.1088/1674-1056/abd2a6 Abstract （456）   HTML （5）    PDF （3103KB）（281）       Knowledge map    The van der Waals (vdW) heterostructures of bilayer transition metal dichalcogenide obtained by vertically stacking have drawn increasing attention for their enormous potential applications in semiconductors and insulators. Here, by using the first-principles calculations and the phonon Boltzmann transport equation (BTE), we studied the phonon transport properties of WS2/WSe2 bilayer heterostructures (WS2/WSe2-BHs). The lattice thermal conductivity of the ideal WS2/WSe2-BHs crystals at room temperature (RT) was 62.98 W/mK, which was clearly lower than the average lattice thermal conductivity of WS2 and WSe2 single layers. Another interesting finding is that the optical branches below 4.73 THz and acoustic branches have powerful coupling, mainly dominating the lattice thermal conductivity. Further, we also noticed that the phonon mean free path (MFP) of the WS2/WSe2-BHs (233 nm) was remarkably attenuated by the free-standing monolayer WS2 (526 nm) and WSe2 (1720 nm), leading to a small significant size effect of the WS2/WSe2-BHs. Our results systematically demonstrate the low optical and acoustic phonon modes-dominated phonon thermal transport in heterostructures and give a few important guidelines for the synthesis of van der Waals heterostructures with excellent phonon transport properties. Select Designing thermal demultiplexer: Splitting phonons by negative mass and genetic algorithm optimization Yu-Tao Tan(谭宇涛), Lu-Qin Wang(王鲁钦), Zi Wang(王子), Jiebin Peng(彭洁彬), and Jie Ren(任捷) Chin. Phys. B, 2021, 30 (3): 036301.   DOI: 10.1088/1674-1056/abd68b Abstract （420）   HTML （1）    PDF （1321KB）（204）       Knowledge map    We propose the concept of thermal demultiplexer, which can split the heat flux in different frequency ranges into different directions. We demonstrate this device concept in a honeycomb lattice with dangling atoms. From the view of effective negative mass, we give a qualitative explanation of how the dangling atoms change the original transport property. We first design a two-mass configuration thermal demultiplexer, and find that the heat flux can flow into different ports in corresponding frequency ranges roughly. Then, to improve the performance, we choose the suitable masses of dangling atoms and optimize the four-mass configuration with genetic algorithm. Finally, we give out the optimal configuration with a remarkable effect. Our study finds a way to selectively split spectrum-resolved heat to different ports as phonon splitter, which would provide a new means to manipulate phonons and heat, and to guide the design of phononic thermal devices in the future. Select Enhanced thermoelectric properties in two-dimensional monolayer Si2BN by adsorbing halogen atoms Cheng-Wei Wu(吴成伟), Changqing Xiang(向长青), Hengyu Yang(杨恒玉), Wu-Xing Zhou(周五星), Guofeng Xie(谢国锋), Baoli Ou(欧宝立), and Dan Wu(伍丹) Chin. Phys. B, 2021, 30 (3): 037304.   DOI: 10.1088/1674-1056/abd163 Abstract （422）   HTML （2）    PDF （2497KB）（159）       Knowledge map    Using the first principles calculation and Boltzmann transport theory, we study the thermoelectric properties of Si2BN adsorbing halogen atoms (Si2BN-4X, $X=\textF$, Cl, Br, and I). The results show that the adsorption of halogen atoms can significantly regulate the energy band structure and lattice thermal conductivity of Si2BN. Among them, Si2BN-4I has the best thermoelectric performance, the figure of merit can reach 0.50 K at 300 K, which is about 16 times greater than that of Si2BN. This is because the adsorption of iodine atoms not only significantly increases the Seebeck coefficient due to band degeneracy, but also rapidly reduces the phonon thermal conductivity by enhancing phonon scattering. Our work proves the application potential of Si2BN-based crystals in the field of thermoelectricity and the effective method for metal crystals to open bandgaps by adsorbing halogens. Select Nonequilibrium reservoir engineering of a biased coherent conductor for hybrid energy transport in nanojunctions "Bing-Zhong Hu(胡柄中), Lei-Lei Nian(年磊磊), and Jing-Tao Lü(吕京涛) Chin. Phys. B, 2020, 29 (12): 120505.   DOI: 10.1088/1674-1056/abb3ee Abstract （400）   HTML    PDF （730KB）（137）       Knowledge map    We show that a current-carrying coherent electron conductor can be treated as an effective bosonic energy reservoir involving different types of electron-hole pair excitations. For weak electron-boson coupling, hybrid energy transport between nonequilibrium electrons and bosons can be described by a Landauer-like formula. This allows for unified account of a variety of heat transport problems in hybrid electron-boson systems. As applications, we study the non-reciprocal heat transport between electrons and bosons, thermoelectric current from a cold-spot, and electronic cooling of the bosons. Our unified framework provides an intuitive way of understanding hybrid energy transport between electrons and bosons in their weak coupling limit. It opens the way of nonequilibrium reservoir engineering for efficient energy control between different quasi-particles at the nanoscale. Select A phononic rectifier based on carbon schwarzite host-guest system Zhongwei Zhang(张忠卫), Yulou Ouyang(欧阳宇楼), Jie Chen(陈杰), and Sebastian Volz Chin. Phys. B, 2020, 29 (12): 124402.   DOI: 10.1088/1674-1056/abbbf9 Abstract （352）   HTML    PDF （1624KB）（148）       Knowledge map    Thermal rectification is a promising way to manipulate the heat flow, in which thermal phonons are spectrally and collectively controlled. As phononic devices are mostly relying on monochromatic phonons, in this work we propose a phononic rectifier based on the carbon schwarzite host-guest system. By using molecular dynamic simulations, we demonstrate that the phononic rectification only happens at a specific frequency of the hybridized mode for the host-guest system, due to its strong confinement effect. Moreover, a significant rectification efficiency, ∼ 134 %, is observed, which is larger than most of the previously observed efficiencies. The study of length and temperature effects on the phononic rectification shows that the monochromaticity and frequency of the rectified thermal phonons depend on the intrinsic anharmonicity of the host-guest system and that the on-center rattling configuration with weak anharmonicity is preferable. Our study provides a new perspective on the rectification of thermal phonons, which would be important for controlling monochromatic thermal phonons in phononic devices. Select Reduction of interfacial thermal resistance of overlapped graphene by bonding carbon chains Yuwen Huang(黄钰文), Wentao Feng(冯文韬), Xiaoxiang Yu(余晓翔), Chengcheng Deng(邓程程), and Nuo Yang(杨诺) Chin. Phys. B, 2020, 29 (12): 126303.   DOI: 10.1088/1674-1056/abc677 Abstract （465）   HTML    PDF （919KB）（150）       Knowledge map    Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance are of great importance for thermal management and modulation. Herein, the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains as shown by molecular dynamics simulations. And the analytical model (phonon weak couplings model, PWCM) is utilized to analyze and explain the two-dimensional thermal transport mechanism at the cross-interface. An order of magnitude reduction of the interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain. Interestingly, the decreasing rate of the interfacial thermal resistance slows down gradually with the increasing number of carbon chains, which can be explained by the proposed theoretical relationship based on analytical model. Moreover, by the comparison of PWCM and the traditional simplified model, the accuracy of PWCM is demonstrated in the overlapped graphene nanoribbons. This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management. Select A polaron theory of quantum thermal transistor in nonequilibrium three-level systems Chen Wang(王晨), Da-Zhi Xu(徐大智) Chin. Phys. B, 2020, 29 (8): 080504.   DOI: 10.1088/1674-1056/ab973b Abstract （542）   HTML    PDF （855KB）（146）       Knowledge map    We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polaron-transformed Redfield equation combined with full counting statistics. The steady state heat currents are obtained via this unified approach over a wide region of system-bath coupling, and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits, respectively. A giant heat amplification phenomenon emerges in the strong system-bath coupling limit, where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism. Moreover, the heat amplification is also exhibited with moderate coupling strength, which can be properly explained within the polaron framework. Select Scaling behavior of thermal conductivity in single-crystalline α-Fe2O3 nanowires Qilang Wang(王啟浪), Yunyu Chen(陈允玉), Adili Aiyiti(阿地力·艾依提), Minrui Zheng(郑敏锐), Nianbei Li(李念北), Xiangfan Xu(徐象繁) Chin. Phys. B, 2020, 29 (8): 084402.   DOI: 10.1088/1674-1056/ab90f0 Abstract （574）   HTML    PDF （1530KB）（102）       Knowledge map    Unveiling the thermal transport properties of various one-dimensional (1D) or quasi-1D materials like nanowires, nanotubes, and nanorods is of great importance both theoretically and experimentally. The dimension or size dependence of thermal conductivity is crucial in understanding the phonon-phonon interaction in the low-dimensional systems. In this paper, we experimentally investigate the size-dependent thermal conductivity of individual single crystalline α-Fe2O3 nanowires collaborating the suspended thermal bridge method and the focused electron-beam self-heating technique, with the sample diameter (d) ranging from 180 nm to 661 nm and length (L) changing from 4.84 μm to 20.73 μm. An empirical relationship for diameter-/length-dependent thermal conductivity is obtained, which shows an approximately linear dependence on the aspect ratio (L/(1+Cd)) at T=300 K, where C is a fitting parameter. This is related to the boundary scattering and diameter effect of α-Fe2O3 nanowires although rigorous calculations are needed to confirm the result. Select Ultra-low thermal conductivity of roughened silicon nanowires: Role of phonon-surface bond order imperfection scattering Heng-Yu Yang(杨恒玉), Ya-Li Chen(陈亚利), Wu-Xing Zhou(周五星), Guo-Feng Xie(谢国锋), Ning Xu(徐宁) Chin. Phys. B, 2020, 29 (8): 086502.   DOI: 10.1088/1674-1056/ab99af Abstract （546）   HTML    PDF （706KB）（161）       Knowledge map    The ultra-low thermal conductivity of roughened silicon nanowires (SiNWs) can not be explained by the classical phonon-surface scattering mechanism. Although there have been several efforts at developing theories of phonon-surface scattering to interpret it, but the underlying reason is still debatable. We consider that the bond order loss and correlative bond hardening on the surface of roughened SiNWs will deeply influence the thermal transport because of their ultra-high surface-to-volume ratio. By combining this mechanism with the phonon Boltzmann transport equation, we explicate that the suppression of high-frequency phonons results in the obvious reduction of thermal conductivity of roughened SiNWs. Moreover, we verify that the roughness amplitude has more remarkable influence on thermal conductivity of SiNWs than the roughness correlation length, and the surface-to-volume ratio is a nearly universal gauge for thermal conductivity of roughened SiNWs. Select First principles calculations on the thermoelectric properties of bulk Au2S with ultra-low lattice thermal conductivity Y Y Wu(伍义远), X L Zhu(朱雪良), H Y Yang(杨恒玉), Z G Wang(王志光), Y H Li(李玉红), B T Wang(王保田) Chin. Phys. B, 2020, 29 (8): 087202.   DOI: 10.1088/1674-1056/ab973c Abstract （716）   HTML    PDF （3634KB）（164）       Knowledge map    Sulfide nanocrystals and their composites have shown great potential in the thermoelectric (TE) field due to their extremely low thermal conductivity. Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized. Herein, we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory, which provides the basis for its further experimental studies. Our results indicate that the highly twofold degeneracy of the bands appears at the Γ point in the Brillouin zone, resulting in a high Seebeck coefficient. Besides, Au2S exhibits an ultra-low lattice thermal conductivity ( ~0.88 W·m-1·K-1 at 700 K). At 700 K, the thermoelectric figure of merit of the optimal p-type doping is close to 1.76, which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K. Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.