Ab-initio Theory of Fourier-transformed Quasiparticle Interference Maps and Application to the Topological Insulator Bi$_2$Te$_3$

Universal signatures of Fermi arcs in quasiparticle interference on the surface of Weyl semimetals

Weyl semimetals constitute a newly discovered class of three-dimensional topological materials with linear touchings of valence and conduction bands in the bulk. The most striking property of topological origin in these materials, so far unequivocally observed only in photoemission experiments, is the presence of open constant-energy contours at the boundary --- the so-called Fermi arcs. In this work, we establish the universal characteristics of Fermi-arc contributions to surface quasiparticle interference. Using a general phenomenological model, we determine the defining interference pattern…

Exact analysis on the singularity of the joint density of states and its relationship to the quasiparticle interference

Singularities of the joint density of states (JDOS) and Fourier-transformed local density of states (FT-LDOS) correspond to the hot spots in quasiparticle interference patterns. In this paper the singularity of JDOS is analyzed exactly, with three types of singularities being classified. In particular, the third type of singularities are found exactly to be envelopes of the contours of constant energy. Remarkably, we show that JDOS and FT-LDOS have the same singular points. Approaching to the singular points, both quantities diverge complementarily in an inverse-square-root manner if the joint…

重金属/铁双层膜中磁性斯格明子准粒子的化学势

Chemical potential of magnetic skyrmion quasiparticles in heavy metal/iron bilayers

该研究利用基于从头算参数的元动力学蒙特卡罗模拟，计算两种重金属/铁双层膜中自由能随拓扑荷的变化，确定斯格明子与反斯格明子化学势的温度及磁场依赖。

从头计算方法用于吸附质在超薄绝缘体上的能量对齐和电荷态预测

An ab initio approach to energy alignment and charge-state prediction of adsorbates on ultrathin insulators

本文提出一种基于第一性原理的计算方法，用于确定吸附质在氧化物/金属基底上的能量对齐，通过GW计算获得离子化势和电子亲和能，量化电子带隙极化，评估费米能钉扎，并确定工作函数变化，为分子量子比特和有机电子界面的高通量筛选提供高效框架。

Theory of quasiparticle interference in mirror symmetric 2D systems and its application to surface states of topological crystalline insulators

We study symmetry protected features in the quasiparticle interference (QPI) pattern of 2D systems with mirror symmetries and time-reversal symmetry, around a single static point impurity. We show that, in the Fourier transformed local density of states (FT-LDOS), $ρ(\bq,ω)$, while the position of high intensity peaks generically depends on the geometric features of the iso-energy contour at energy $ω$, the \emph{absence} of certain peaks is guaranteed by the opposite mirror eigenvalues of the two Bloch states that are (i) on the mirror symmetric lines in the Brillouin zone (BZ) and (ii) separ…

Triple point semimetal and topological phase transitions in NaCu$_{3}$Te$_{2}$

Quasiparticle excitations of free electrons in condensed-matter physics, characterized by the dimensionality of the band crossing, can find their elementary-particle analogs in high-energy physics, such as Majorana, Weyl, and Dirac fermions. While crystalline symmetry allows more quasiparticle excitations and exotic fermions to emerge. Using symmetry analysis and {\it ab-initio} calculations, we propose that the 3D honeycomb crystal NaCu$_3$Te$_2$ hosts triply degenerate nodal points (TDNPs) which are perfectly separated from the bulk states. We find a tunable phase transition between TDNPs an…

Current-induced spin polarization at the surface of metallic films: a theorem and an ab initio calculation

The broken inversion symmetry at the surface of a metallic film (or, more generally, at the interface between a metallic film and a different metallic or insulating material) greatly amplifies the influence of the spin-orbit interaction on the surface properties. The best known manifestation of this effect is the momentum-dependent splitting of the surface state energies (Rashba effect). Here we show that the same interaction also generates a spin-polarization of the bulk states when an electric current is driven through the bulk of the film. For a semi-infinite jellium model, which is represe…

Impurity scattering and size quantization effects in a single graphene nanoflake

By using Fourier-transform scanning tunneling spectroscopy we measure the interference patterns produced by the impurity scattering of confined Dirac quasiparticles in epitaxial graphene nanoflakes. Upon comparison of the experimental results with tight-binding calculations of realistic model flakes, we show that the characteristic features observed in the Fourier-transformed local density of states are related to scattering between different transverse modes (sub-bands) of a graphene nanoflake and allow direct insight into the electronic spectrum of graphene. We also observe a strong reductio…

Excitonic effects in the optical properties of SiC sheet and nanotubes

The quasiparticle band structure and optical properties of single-walled zigzag and armchair SiC nanotubes (SiC-NTs) as well as single SiC sheet are investigated by ab initio many-body calculations using the GW and the GW plus Bethe-Salpeter equation (GW+BSE) approaches, respectively. Significant GW quasiparticle corrections of more than 1.0 eV to the Kohn-Sham band gaps from the local density approximation (LDA) calculations are found. The GW self-energy corrections transform the SiC sheet from a indirect LDA band gap to a direct band gap material. Furthermore, the quasiparticle band gaps of …

通过表面合成与还原相结合的方法制备用于自旋子探测的自旋1/2海森堡反铁磁链

Fabrication of Spin-1/2 Heisenberg Antiferromagnetic Chains via Combined On-surface Synthesis and Reduction for Spinon Detection

本研究通过表面合成结合原位还原的方法，制备出长度可控的自旋1/2海森堡反铁磁链，验证了其无隙自旋激发特征与符合理论计算的自旋子色散，为构建目标量子自旋系统提供了新途径。

Bi$_{\mathbf{2}}$Se$_{\mathbf{3}}$终止的(PbSe)$_{\mathbf 5}$(Bi$_{\mathbf 2}$Se$_{\mathbf 3}$)$_{\mathbf 6}$表面的准粒子干涉

Quasiparticle interference on the surface of Bi$_{\mathbf{2}}$Se$_{\mathbf{3}}$ terminated (PbSe)$_{\mathbf 5}$(Bi$_{\mathbf 2}$Se$_{\mathbf 3}$)$_{\mathbf 6}$

本研究利用STM和DFT表征母体化合物PSBS的表面，发现其原生缺陷势能无序极小，通过QPI成像重构了表面态色散关系，揭示了类Rashba劈裂及源于散射势三重对称性的低能散射图样变化。