MoS $_2$的本征晶格热导率是设计MoS $_2$基纳米电子器件的一个重要方面。我们利用第一性原理计算研究了MoS $_2$的晶格动力学性质。利用声子的玻尔兹曼输运方程计算了单层MoS $_2$的本征热导率。得到的热导率与测量值吻合良好。计算了声学声子和光学声子对晶格热导率的贡献。研究了热导率的尺寸依赖性。
英文摘要：
The intrinsic lattice thermal conductivity of MoS$_2$ is an important aspect in the design of MoS$_2$-based nanoelectronic devices. We investigate the lattice dynamics properties of MoS$_2$ by first principles calculations. The intrinsic thermal conductivity of single-layer MoS$_2$ is calculated using the Boltzmann transport equation for phonons. The obtained thermal conductivity agrees well with the measurements. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. The size dependence of thermal conductivity is investigated as well.
Intrinsic characteristic radius drives phonon anomalies in Janus transition metal dichalcogenide nanotubes
School of Mechatronic Engineering and Automation, Shanghai University（上海大学机电工程与自动化学院）；Shanghai Key Laboratory of Mechanics in Energy Engineering, Shanghai Institute of Applied Mathematics and Mechanics, Shanghai Frontier Science Center of Mechanoinformatics, School of Mechanics and Engineering Science, Shanghai University（上海大学力学与工程科学学院）
Polar phonons and intrinsic dielectric response of the ferromagnetic insulating spinel CdCr$_2$S$_4$ from first principles
本文从第一性原理出发研究了铁磁尖晶石CdCr $_2$ S $_4$的介电性质。在LSDA+U模型下，利用冻结声子和Berry相位技术计算了带心声子和玻恩有效电荷。我们发现，所有的红外活性声子是相当稳定的立方空间群内。计算的静态介电常数与以前的测量结果吻合得很好。这些结果表明，最近观察到的异常介电行为在CdCr $_2$ S $_4$是不是由于极性模式的软化。我们建议进一步的实验来阐明这一点。
Transport of electrons at high electric fields is investigated in an intrinsic three-dimensional Dirac semimetal cadmium arsenide, considering the scattering of electrons from acoustic and optical phonons. Screening and hot phonon effect are taken in to account. Expressions for the hot electron mobility $μ$ and power loss $P$ are obtained as a function of electron temperature $T_e$. The dependence of drift velocity $v_d$ on electric field $E$ and electron density $n_e$ has been studied. Hot phonon effect is found to set in the saturation of $v_d$ at relatively low $E$ and significantly degrade…
Machine learning techniques are used to explore the intrinsic origins of the hydrodynamic thermal transport and to find new materials interesting for science and engineering. The hydrodynamic thermal transport is governed intrinsically by the hydrodynamic scale and the thermal conductivity. The correlations between these intrinsic properties and harmonic and anharmonic properties, and a large number of compositional (290) and structural (1224) descriptors of 131 crystal compound materials are obtained, revealing some of the key descriptors that determines the magnitude of the intrinsic hydrody…
The paper presents the first-principle calculation of the electron-phonon coupling and the temperature dependence of the intrinsic electrical resistivity of the zirconium-hydrogen system with various hydrogen concentrations. The nature of the anomalous decrease in the electrical resistivity of the Zr-H system with the increase of hydrogen concentration (at the high concentrations of H/Zr$>$1.5) was studied. It was found that the hydrogen concentration, where the resistivity starts to decrease, is very close to the critical concentration of the $δ-\varepsilon$ phase transition. It was shown tha…
Phonon-phonon anharmonic effects have a strong influence on the phonon spectrum; most prominent manifestation of these effects are the softening (shift in frequency) and broadening (change in FWHM) of the phonon modes at finite temperature. Using Raman spectroscopy, we studied the temperature dependence of the FWHM and Raman shift of $\mathrm{E_{2g}^1}$ and $\mathrm{A_{1g}}$ modes for single-layer and natural bilayer MoS$_2$ over a broad range of temperatures ($8 < $T$ < 300$ K). Both the Raman shift and FWHM of these modes show linear temperature dependence for $T>100$ K, whereas they become …
Many promising optoelectronic devices, such as broadband photodetectors, nonlinear frequency converters, and building blocks for data communication systems, exploit photoexcited charge carriers in graphene. For these systems, it is essential to understand, and eventually control, the cooling dynamics of the photoinduced hot-carrier distribution. There is, however, still an active debate on the different mechanisms that contribute to hot-carrier cooling. In particular, the intrinsic cooling mechanism that ultimately limits the cooling dynamics remains an open question. Here, we address this que…
Atomic undercoordination, charge injection, mechanical and thermal activation mediate the properties of a material intrinsically by bond relaxation from one equilibrium to another while the phonon spectrometrics probes the ever-unexpected information of the binding energy density, atomic cohesive energy, single bond force constant, crystal elastic modulus, Debye temperature and the abundance-length-stiffness transition of bonds under perturbation.
Giant Intrinsic Carrier Mobilities in Graphene and Its Bilayer
我们研究了石墨烯及其双层中电子输运的温度依赖性，发现极低的电子-声子散射率，这对室温下可能的载流子迁移率设置了基本限制。我们的测量表明，迁移率显着高于200，000 cm 2/Vs是可以实现的，如果外在的障碍被消除。在大约200 K以上观察到的电阻率的急剧（阈值状）增加是出乎意料的，但是可以在波纹石墨烯片的模型内定性地理解，其中散射发生在波纹内弯曲声子上。
Domain Walls Stabilized by Intrinsic Phonon Modes and Engineered Defects Enable Robust Ferroelectricity in HfO2
School of Integrated Circuits, Peking University（北京大学集成电路学院）；Advanced Instrumental Analysis Center, School of Chemical Engineering and Technology, Tianjin University（天津大学化学工程与技术学院先进仪器分析中心）
Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus
本文提出了一种适用于单层黑磷（BP）的各向异性二维半导体中的单声子和双声子载流子散射理论。我们表明，在对比石墨烯，其中双声子过程中，由于弯曲声子的散射占主导地位，在任何实际相关的温度和独立的载流子浓度$n$，双声子散射BP是不太重要的，可以被认为是可以忽略不计的$n\gtrsim10^{13}$厘米$^{-2}$。然而，在较小的$n$，声子进入基本上是非谐的制度。与在BP的主方向之间不表现出强各向异性的空穴迁移率（$μ_{xx}/μ_{yy}\sim1.4$ at $n=10^{13}$ cm $^{-2}$ and $T=300$ K）相比，发现电子迁移率显著更各向异性（$μ_{xx}/μ_{yy}\sim6.2$）。对于空穴（电子），$μ_{xx}$的绝对值不超过250（700）cm $^2$ V $^{-1}$ s $^{-1}$，这可以被认为是室温下BP中迁移率的上限。
Analytical theory of large size intrinsic localized modes (ILMs) in anharmonic two-atomic chain is presented. It is shown that ILMs with frequencies close to the borders of phonon gap are govern by quartic anharmonicity while the effect of cubic anharmonicity is essentially reduced. This reduction effect is a consequence of small amplitude of vibrations of every second atom. As a result, an ILM cannot split down from the optical phonon band, in contradiction with the commonly accepted point of view. But it can spit up from the top of the acoustic phonon band making possible the existence of th…
Designing new quantum materials with long-lived electron spin states urgently requires a general theoretical formalism and computational technique to reliably predict intrinsic spin relaxation times. We present a new, accurate and universal first-principles methodology based on Lindbladian dynamics of density matrices to calculate spin-phonon relaxation time ($τ_s$) of solids with arbitrary spin mixing and crystal symmetry. This method describes contributions of Elliott-Yafet (EY) and D'yakonov-Perel' (DP) mechanisms to spin relaxation for systems with and without inversion symmetry on an equa…
The anharmonicity of phonons in solid is ultimately rooted in the chemical bonding. However, the direct connection between phonon anharmoncity and chemical bonding is difficult to make experimentally or theoretically, due mainly to their complicated lattice structures. Here, with the help of density functional theory based calculations, we discovery that electrostatic inter-layer coupling in Bi$_2$O$_2$X (X=S,Se,Te) leads to intrinsically low lattice thermal conductivity. We explain our discovery by the strong anharmonic chemical bonding between Bi and chalcogen atoms. Our results shed light o…
The intrinsic charge transport of stanene is investigated by using density function theory and density function perturbation theory coupled with Boltzmann transport equations from first principles. The accurate Wannier interpolations are applied to calculate the charge carrier scatterings with all branches of phonons with dispersion contribution. The intrinsic carrier mobilities are predicted to be 2~3$\times10^3$ cm$^2$/(V s) at 300 K, and we find that the intervalley scatterings from the out-of-plane and transverse acoustic phonon modes dominate the carrier relaxation. In contrast, the intri…
Electron-phonon(e-ph) interaction in Ca2N monolayer, the first electrene material with two-dimensional(2D) electron gas floating in free space, is expected to be very weak and such a character can be used to design weak-scattering transport channels. Therefore, it is highly desirable to quantitatively evaluate the carrier mobility of electrene. In this study, e-ph interaction in Ca2N monolayer is investigated using a precise Wannier interpolation-based first principles technique. The calculated e-ph coupling matrix elements of Ca2N monolayer are indeed small compared to other 2D materials such…
The observation of replica bands by angle-resolved photoemission spectroscopy has ignited interest in the study of electron-phonon coupling at low carrier densities, particularly in monolayer FeSe/SrTiO$_3$, where the appearance of replica bands has motivated theoretical work suggesting that the interfacial coupling of electrons in the FeSe layer to optical phonons in the SrTiO$_3$ substrate might contribute to the enhanced superconducting pairing temperature. Alternatively, it has also been recently proposed that such replica bands might instead originate from extrinsic final state losses ass…
Two-dimensional (2D) semiconductors have demonstrated great potential for next-generation electronics and optoelectronics. An important property for these applications is the phonon-limited charge carrier mobility. The common approach to calculate the mobility from first principles relies on the interpolation of the electron-phonon coupling (EPC) matrix. However, it neglects the scattering by the dynamical quadrupoles generated by phonons, limiting its accuracy. Here we present a first-principles method to incorporate the quadrupole scattering, which results in a much better interpolation qual…
Recently, massive efforts have been done on controlling thermal transport via coherent phonons in the various periodic nanostructures. However, the intrinsic lattice difference between the constituent materials inevitably generates the disorder at the interfaces, thus limiting the opportunity of directly observing the coherent phonon transport. Here, we investigate the controllability and visualization of the coherent phonon transport in a periodic MoS2/MoSe2 arrayed heterostructure with minimum lattice mismatching using non-equilibrium molecular dynamics simulation. It is found that the coher…
Measurement of intrinsic Dirac fermion cooling on the surface of a topological insulator Bi$_2$Se$_3$ using time- and angle-resolved photoemission spectroscopy
我们进行时间和角度分辨的光电子能谱的原型拓扑绝缘体Bi $_2$ Se $_3$的表面和体电子光激发后的超快动力学研究。通过分析表面态和体能带谱的演化，分别得到了它们的电子温度和化学势弛豫动力学。这些动力学揭示了强声子辅助的表面-体耦合在高晶格温度和总抑制在低晶格温度的表面和体之间的非弹性散射。在这个低温制度下，独特的冷却狄拉克费米子在TI的声学声子表现出通过幂律依赖的表面温度衰减速率载流子密度。
We report resonant Raman spectroscopy of neutral excitons X$^0$ and intravalley trions X$^-$ in hBN-encapsulated MoS$_2$ monolayer embedded in a nanobeam cavity. By temperature tuning the detuning between Raman modes of MoS$_2$ lattice phonons and X$^0$/X$^-$ emission peaks, we probe the mutual coupling of excitons, lattice phonons and cavity vibrational phonons. We observe an enhancement of X$^0$-induced Raman scattering and a suppression for X$^-$-induced, and explain our findings as arising from the tripartite exciton-phonon-phonon coupling. The cavity vibrational phonons provide intermedia…
Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2
石墨烯中的线性色散关系[1，2]产生了令人惊讶的预测：由于各向同性散射体（例如白噪声无序[3]或声子[4-8]）引起的电阻率与载流子密度n无关。在这里，我们表明声学声子散射[4-6]确实与n无关，并且在室温（RT）下石墨烯的电阻率仅为30欧姆。在技术相关的载流子密度为10^12 cm^-2时，电声声子散射的平均自由程大于2微米，本征迁移率极限为2x10^5 cm ^2/Vs，超过了已知最高的无机半导体（InSb，~7.7x10^4 cm ^2/Vs[9]）和半导体碳纳米管（~1x10^5 cm ^2/Vs[10]）。我们还表明，SiO2衬底[11，12]的表面声子的非本征散射增加了高于~200 K的强温度依赖性电阻率[8]，将RT迁移率限制为~4x10^4 cm^2/Vs，指出了石墨烯器件衬底选择的重要性[13]。
The reduced dielectric screening in atomically thin transition metal dichalcogenides allows to study the hydrogen-like series of higher exciton states in optical spectra even at room temperature. The width of excitonic peaks provides information about the radiative decay and phonon-assisted scattering channels limiting the lifetime of these quasi-particles. While linewidth studies so far have been limited to the exciton ground state, encapsulation with hBN has recently enabled quantitative measurements of the broadening of excited exciton resonances. Here, we present a joint experiment-theory …
Realization of Room-Temperature Phonon-limited Carrier Transport in Monolayer MoS2 by Dielectric and Carrier Screening
我们发现，通过结合高k介质衬底和高密度的载流子，库仑杂质可以有效地屏蔽，导致前所未有的室温迁移率约150 cm 2/Vs的单层二硫化钼。高质量的样品使我们能够定量提取受库仑杂质、本征和表面光学声子限制的迁移率分量，并研究它们随温度、载流子密度和介电常数的变化。我们的理论分析和实验数据之间的良好的协议明确表明，室温声子限制的传输实现在单层二硫化钼，这是电子器件应用的必要因素。
In the context of recent experimental observations of an unexpectedly large thermal Hall conductivity, $κ_H$, in insulating $\mathrm{La_2CuO_4}$ (LCO) and $\mathrm{SrTiO_3}$ (STO), we theoretically explore conditions under which acoustic phonons can give rise to such a large $κ_H$. Both the intrinsic and extrinsic contributions to $κ_H$ are large in proportion to the dielectric constant, $ε$, and the flexoelectric coupling, $F$. While the intrinsic contribution is still orders of magnitude smaller than the observed effect, an extrinsic contribution proportional to the phonon mean free path app…
Two-dimensional (2D) semiconductors have demonstrated great potential for next-generation electronics and optoelectronics. However, the current 2D semiconductors suffer from intrinsically low carrier mobility at room temperature, which significantly limits its applications. Here we discover a variety of new 2D semiconductors with mobility one order of magnitude higher than the current ones. The discovery is made by developing effective descriptors for high-throughput computationally screening of the 2D materials database, followed by using state-of-the-art first principles method to accurately…
When Cubic Is Not Isotropic: Phonon-Exciton Decoupling in CuInSnS$_4$ Single Crystals
Helmholtz-Zentrum Berlin für Materialien und Energie（柏林赫尔姆霍兹中心）；University of Manchester（曼彻斯特大学）；University of Zurich（苏黎世大学）；University of Basel（巴塞尔大学）；University of Cambridge（剑桥大学）；Freie Universität Berlin（柏林自由大学）
Adaptation of Wallace's Approach to the Specific Heat of Elemental Solids with Significant Intrinsic Anharmonicity, Particularly the Light Actinide Metals
