The possibility to inject a single electron into ballistic conductors is at the basis of the new field of electron quantum optics. Here, we consider a single electron injection into the helical edge channels of a topological insulator. Their counterpropagating nature and the unavoidable presence of electron-electron interactions dramatically affect the time evolution of the single wavepacket. Modeling the injection process from a mesoscopic capacitor in presence of non-local tunneling, we focus on the time resolved charge and energy packet dynamics. Both quantities split up into counterpropagating contributions whose profiles are strongly affected by the interactions strength. In addition, stronger signatures are found for the injected energy, which is also affected by the finite width of the tunneling region. Indeed, the energy flow can be controlled by tuning the injection parameters and we demonstrate that, in presence of non-local tunneling, it is possible to achieve situation in which charge and energy flow in opposite directions.
Supermoiré domain-resolved effective Hamiltonians and valley topology in helical multilayer graphene
Seoul National University（首尔大学）；Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST（加泰罗尼亚纳米科学和纳米技术研究所（ICN2，西班牙高等科学研究委员会和巴塞罗那独立系统大学））；University of Seoul（首尔大学）
We propose a versatile setup that allows performing spin-resolved spectroscopy of helical Andreev bound states, proving their existence and therefore the topological nature of the Josephson junction that hosts them. The latter is realized on the helical edge of a 2D topological insulator, proximitized with two superconducting electrodes. The spectroscopic analysis is enabled by a quantum point contact, which couples the junction with another helical edge acting as a spin-sensitive prove. By means of straightforward transport measurements, it is possible to detect the particular spin structure …
The time-dependent state of a classical spin locally exchange coupled to an edge site of a Kane-Mele model in the topologically non-trivial phase is studied numerically by solving the full set of coupled microscopic equations of motion for the spin and the electron system. Dynamics in the long-time limit is accessible thanks to dissipative boundary conditions, applied to all but the zigzag edge of interest. We study means to control the state of the spin via transport of a spin-polarization cloud through the helical edge states. The cloud is formed at a distant edge site using a local magnetic…
Observation of a warped helical spin-texture in Bi$_2$Se$_3$ from circular dichroism angle-resolved photoemission spectroscopy
拓扑表面态与左旋和右旋圆偏振光的微分耦合是拓扑绝缘体的许多光自旋电子学应用的基础。在这里，我们报告的圆二色性的直接证据，从表面状态的Bi $_2$ Se $_3$使用基于激光的飞行时间角分辨光电子能谱。通过采用一种新的样品旋转分析，我们解决了不寻常的调制的圆二色性光电发射图案作为能量和动量的函数，这完美地模仿了预测，但迄今未观察到的三维扭曲的自旋纹理的表面状态。通过发展拓扑表面态光电子发射的微观理论，我们表明，这种相关性是自旋轨道耦合的自然结果。这些结果表明，我们的技术可能是一个强大的探针的自旋-轨道耦合材料的自旋织构一般。
Materials with spin-momentum locked surface or interface states provide an interesting playground for studying physics and application of charge-spin current conversion. To characterize their non-equilibrium magnetic and transport properties in the presence of a time-dependent external magnetic field and a spin injection from a contact, we introduce three macroscopic variables: a vectorial helical magnetization, a scaler helical magnetization, and the conventional magnetization. We derive a set of closed dynamic equations for these variables by using the spinor Boltzmann approach with the coll…
First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy
具有类光色散关系或锥形狄拉克光谱的电子系统，如石墨烯和铋，最近被证明在高磁场中具有不寻常的集体态。这种状态是可能的，因为它们的类光电子是手性的自旋对，这意味着它们的传播方向与描述它们在晶格中位置的称为赝自旋的量有关。量子材料研究的一个新兴方向是操纵原子自旋轨道耦合来模拟自旋相关磁场的效应，试图实现物质的新自旋相。这种效应已经被提出来实现由螺旋形的不成对狄拉克锥组成的系统，这意味着它们的传播方向与电子自旋本身有关，这在石墨烯或铋中是禁止存在的。没有自旋分辨的测量，拓扑序的实验存在性不能确定。在这里，我们报告的Bi 2 Te 3和Bi{2-x} MnxTe 3系列，这被发现表现出一个单一的螺旋狄拉克锥，是完全自旋极化的六边形表面的自旋和角度分辨的光电发射研究。我们观察到的一个间隙在体自旋简并带和自旋分辨表面狄拉克节点接近化学势表明，低能动力学的Bi 2 Te 3是由不成对的自旋螺旋狄拉克模式。我们的自旋纹理测量证明了在这种材料类中首次存在罕见的拓扑相，并表明其适用于超越手性品种或传统石墨烯的新型2D狄拉克自旋器件应用。
Injection of a radio frequency (RF) current was used to phase lock the SHNO to the TRSKM. The out of plane magnetization was detected by means of the polar magneto optical Kerr effect (MOKE). However, longitudinal MOKE images were dominated by an artifact arising from the edges of the Au NCs. Time resolved imaging revealed the simultaneous excitation of a non-linear `bullet' mode at the centre of the device, once the DC current exceeded a threshold value, and ferromagnetic resonance (FMR) induced by the RF current. However, the FMR response observed for sub-critical DC current values exhibits …
Cascade of topological phase transitions and revival of topological zero modes in imperfect double helical liquids
Institute of Physics, Academia Sinica（中央研究院物理研究所）；Department of Electronics and Electrical Engineering, National Yang Ming Chiao Tung University（国立阳明交通大学电子工程学系）；Physics Division, National Center for Theoretical Sciences（国家理论科学中心物理组）
We develop a theory of finite-temperature momentum-resolved tunneling spectroscopy (MRTS) for disordered, interacting two-dimensional topological-insulator edges. The MRTS complements conventional electrical transport measurement in characterizing the properties of the helical Luttinger liquid edges. Using standard bosonization technique, we study low-energy spectral function and the MRTS tunneling current, providing a detailed description controlled by disorder, interaction, and temperature, taking into account Rashba spin orbit coupling, interedge interaction and distinct edge velocities. Ou…
Atomic-scale spin sensing of a 2D $d$-wave altermagnet via helical tunneling
University of Science and Technology of China（中国科学技术大学）；The Hong Kong University of Science and Technology（香港科技大学）；IAS Center for Quantum Matter, The Hong Kong University of Science and Technology（香港科技大学量子物质高等研究院中心）；Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China（中国科学技术大学安徽省先进光子科学与技术实验室）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）；The University of Texas at Dallas（德州大学达拉斯分校）；Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所北京凝聚态物理国家研究中心）；Collaborative Innovation Center of Advanced Microstructures（先进微结构协同创新中心）
Time-reversal symmetric charge and spin transport through a molecule comprising two-orbital channels and connected to two leads is analyzed. It is demonstrated that spin-resolved currents are generated when spin-flip processes are accompanied by a flip of the orbital channels. This surprising finding does not contradict Bardarson's theorem [J. H. Bardarson, J. Phys. A: Math. Theor. 41, 405203 (2008)] for two-terminal junctions: the transmission does possess two pairs of doubly-degenerate eigenvalues as required by the theorem. The spin-filtering effect is explicitly demonstrated for a two-term…
We demonstrate a combined frequency and time domain investigation of injection-locked, constriction-based spin Hall nano-oscillators by Brillouin light scattering (BLS) and time-resolved magneto-optical Kerr effect (TR-MOKE). This was achieved by applying an alternating current in the GHz regime in addition to the direct current which drives auto-oscillations in the constriction. In the frequency domain, we analyze the width of the locking range, the increase in intensity and reduction in linewidth as a function of the applied direct current. Then we show that the injection locking of the auto…
Employing femtosecond laser pulses in front and back side pumping of Au/Fe/MgO(001) combined with detection in two-photon photoelectron emission spectroscopy we analyze local relaxation dynamics of excited electrons in buried Fe, injection into Au across the Fe-Au interface, and electron transport across the Au layer at 0.6 to 2.0 eV above the Fermi energy. By analysis as a function of Au film thickness we obtain the electron lifetimes of bulk Au and Fe and distinguish the relaxation in the heterostructure's constituents. We also show that the excited electrons propagate through Au in a superd…
Organic-inorganic perovskite as a promising candidate for solar energy harvesting has attracted immense interest for its low-cost preparation and extremely high quantum efficiency. However, the fundamental understanding of the photophysics in perovskite remains elusive. In this work, we have revealed two distinct states in MAPbI3 thin films at low temperature through time-resolved photoluminescence spectroscopy (TRPL). In particular, we observe a photo-induced carrier injection from the high energy (HE) state to the low energy (LE) state which has a longer lifetime. The strong interaction betw…
We theoretically investigate optical injection processes, including one- and two-photon carrier injection and two-color coherent current injection, in twisted bilayer graphene with moderate angles. The electronic states are described by a continuum model, and the spectra of injection coefficients are numerically calculated for different chemical potentials and twist angles, where the transitions between different bands are understood by the electron energy resolved injection coefficients. The comparison with the injection in monolayer graphene shows the significance of the interlayer coupling …
We demonstrate the electrical detection of magnon-magnon hybrid dynamics in yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct microwave current injection through the conductive Py layer excites the hybrid dynamics consisting of the uniform mode of Py and the first standing spin wave ($n=1$) mode of YIG, which are coupled via interfacial exchange. Both the two hybrid modes, with Py or YIG dominated excitations, can be detected via the spin rectification signals from the conductive Py layer, providing phase resolution of the coupled dynamics. The phase characterization is …
Spin transport characteristics of graphene has been extensively studied so far. The spin transport along c-axis is however reported by rather limited number of papers. We have studied spin transport characteristics through graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The relatively simple sample structure does not require electrodes on the sample. The graphene layer was prepared by chemical vapor deposition and transferred on Pt film. The quality of graphene layer was characterized by …
Kagome metals AV3Sb5 (A = K, Rb, and Cs) exhibit a unique superconducting ground state coexisting with charge-density wave (CDW), whereas how these characteristics are affected by carrier doping remains unexplored because of the lack of an efficient carrier-doping method. Here we report successful electron doping to CsV3Sb5 by Cs dosing, as visualized by angle-resolved photoemission spectroscopy. We found that the electron doping with Cs dosing proceeds in an orbital-selective way, as characterized by a marked increase in electron filling of the Sb 5pz and V 3dxz/yz bands as opposed to relativ…
Femtosecond Laser-induced Crystallization of Amorphous Sb2Te3 film and Coherent Phonon Spectroscopy Characterization and Optical Injection of Electron Spins
采用飞秒激光辐照晶化技术将非晶Sb_2Te_3薄膜转变为晶化薄膜。利用高灵敏度的相干声子谱（CPS）技术研究了非晶Sb_2Te_3薄膜在辐照后的晶化过程。CPS揭示了对应于晶体Sb 2 Te 3的特征声子模式的两个声子模式的振动强度，随着激光照射能量密度（LIF）的增加而增强，显示出LIF的结晶度的上升，并且飞秒激光照射是一种良好的后处理技术。利用时间分辨圆偏振泵浦-探测光谱研究了激光诱导晶化Sb_2Te_3薄膜的电子自旋弛豫动力学。实验结果证实了自旋相关的光学跃迁选择定则的有效性和基于自旋光栅的类Sb 2 Te 3拓扑绝缘体自旋等离激元集体模瞬态光学探测方案的可行性.
