The in-plane optical phonons around 200 meV in few-layer graphene are investigated utilizing infrared absorption spectroscopy. The phonon spectra exhibit unusual asymmetric features characteristic of Fano resonances, which depend critically on the layer thickness and stacking order of the sample. The phonon intensities in samples with rhombohedral (ABC) stacking are significantly higher than those with Bernal (AB) stacking. These observations reflect the strong coupling between phonons and interband electronic transitions in these systems and the distinctive variation in the joint density of electronic states in samples of differing thickness and stacking order.
我们研究了正则拓扑绝缘体Bi $_2$ Se $_3$的磁光响应，目的是解决一个有争议的问题的电子-声子耦合。磁场引起的反射率的修改是非常明显的红外光谱的一部分，表明强烈的电子-声子耦合。这种耦合导致60 cm $^{-1}$声子模式的不对称线形，并在Fano形式主义内进行分析。分析表明，当回旋共振随声子模简并时，Fano非对称性参数q变号。据我们所知，这是磁场驱动q反转的第一个例子。
Detection of local strain at the nanometer scale with high sensitivity remains challenging. Here we report near-field infrared nano-imaging of local strains in bilayer graphene through probing strain-induced shifts of phonon frequency. As a non-polar crystal, intrinsic bilayer graphene possesses little infrared response at its transverse optical (TO) phonon frequency. The reported optical detection of local strain is enabled by applying a vertical electrical field that breaks the symmetry of the two graphene layers and introduces finite electrical dipole moment to graphene phonon. The activate…
We study the influence of inelastic processes on shot noise and the Fano factor for a one-dimensional double-barrier structure, where resonant tunneling takes place between two terminals. Most studies to date have found, by means of various approximate or phenomenological methods, that shot noise is insensitive to dephasing caused by inelastic scattering. In this paper, we explore the status of this statement by deriving a general Landaur-Büttiker-type formula that expresses the current noise and Fano factor in a one-dimensional conductor through inelastic scattering amplitudes. For a double-b…
Weyl semimetals are 3D phases of matter with topologically protected states that have remarkable macroscopic transport behaviors. As phonon dynamics and electron-phonon scattering play a critical role in the electrical and thermal transport, we pursue a fundamental understanding of the origin of these effects in type-I Weyl semimetals NbAs and TaAs. In the temperature-dependent Raman spectra of NbAs, we reveal a previously unreported Fano lineshape, a signature stemming from the electron-phonon interaction. Additionally, the temperature dependence of the $A_{1}$ phonon linewidths in both NbAs …
Due to their possibility to encode information and realize low-energy-consumption quantum devices, control and manipulation of the valley degree of freedom have been widely studied in electronic systems. In contrast, the phononic counterpart--valley phononics--has been largely unexplored, despite the importance in both fundamental science and practical applications. In this work, we demonstrate that the control of "valleys" is also applicable for phonons in graphene by using a grain boundary. In particular, perfect valley filtering effect is observed at certain energy windows for flexural mode…
In the bilayer ReS$ _{2} $ channel of a field-effect transistor (FET), we demonstrate using Raman spectroscopy that electron doping (n) results in softening of frequency and broadening of linewidth of the in-plane vibrational modes, leaving out-of-plane vibrational modes unaffected. Largest change is observed for the in-plane Raman mode at $\sim$ 151 cm$^{-1} $, which also shows doping induced Fano resonance with the Fano parameter 1/q = -0.17 at doping concentration of $\sim 3.7\times10^{13}$ cm$^{-2} $. A quantitative understanding of our results is provided by first-principles density funct…
On Fano effect in IR spectra of hydrogenated nanodiamonds
Frumkin Institute of physical chemistry and electrochemistry Russian Academy of Sciences（俄罗斯科学院弗鲁姆金物理化学与电化学研究所）；Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences（俄罗斯科学院别列查金高压物理研究所）
We investigate the interaction between a topological insulator nanoparticle and a quantum dot in an impulse magnetic field. Since topological insulators are nonmagnetic, after the impulse has ended only the localised topological surface modes, which are quantised in terms of dipolar bosonic modes, thus coupling dipolarly to the quantum dot. Hence, the hybrid system can be treated as a single bosonic mode interacting with a two-level system, where the coupling strength is quantised in terms of the magnetoelectric polarizability. We implement the interaction of the hybrid with the environment th…
We have studied spectral evolution of the $E_u^1$ phonon line of a topological insulator Bi$_{2-x}$Sr$_x$Se$_3$ with temperature. Unlike the Raman-active phonons, the $E_u^1$ mode demonstrates softening upon cooling the crystal, and the corresponding spectral line acquires a pronounced Fano-like shape at temperatures $T\lesssim100$ K. We interpret the latter effect as a signature of specific coupling of the bulk infrared active phonons to surface Dirac electrons. Using coherent resonant excitation of the $E_u^1$ mode as a surface sensitive tool, we have detected softening of the surface counte…
Shot noise and conductivity at high bias in bilayer graphene: Signatures of electron-optical phonon coupling
研究了双层石墨烯（BLG）片在高偏压和低浴温$T_0=4.2$ K下的电子电导率和散粒噪声。作为偏置的函数，我们发现最初增加的微分电导率，我们归因于自加热。在较高的偏压下，由于光学声子的背散射，电导率饱和甚至下降。电子-声子相互作用也负责在偏置电压$V>0.1$ V的Fano因子的衰减。高偏置电子温度已从散粒噪声测量计算，它上升到$\sim1200$ K在$V=0.75$ V。使用BLG电导率的理论温度依赖性，我们提取一个有效的电子-光学声子散射时间$τ_{e-op}$。在230 nm长的迁移率为$μ=3600$ cm $^2$ V $^{-1}$ s $^{-1}$的BLG样品中，我们发现$τ_{e-op}$随着电压的增加而减小，并且接近于$V=0.6$ V处的带电杂质散射时间$τ_{imp}=60$ fs。
Hyperbolic-enhanced Raman scattering in van der Waals MoOCl2: from Fano resonances to picomolar detection
XPANCEO；University of Chemistry and Technology Prague（布拉格化工大学）；National Graphene Institute (NGI), University of Manchester（曼彻斯特大学国家石墨烯研究所）；National University of Singapore（新加坡国立大学）
