We have determined the spin-orbit scattering length of two-dimensional layered 2H-TaSe2 metallic crystals by detailed characterization of the weak anti-localization phenomena in this strong spin-orbit interaction material. By fitting the observed magneto-conductivity, the spin-orbit scattering length for 2H-TaSe2 is determined to be 17 nm in the few-layer films. This small spin-orbit scattering length is comparable to that of Pt, which is widely used to study the spin Hall effect, and indicates the potential of TaSe2 for use in spin Hall effect devices. In addition to strong spin-orbit coupling, a material must also support large charge currents to achieve spin-transfer-torque via the spin Hall effect. Therefore, we have characterized the room temperature breakdown current density of TaSe2 in air, where the best breakdown current density reaches 3.7$\times$10$^7$ A/cm$^2$. This large breakdown current further indicates the potential of TaSe2 for use in spin-torque devices and two-dimensional device interconnect applications.
We measure the local near-field spin in topological edge state waveguides that emulate the quantum spin Hall effect. We reveal a highly structured spin density distribution that is not linked to a unique pseudospin value. From experimental near-field real-space maps and numerical calculations, we confirm that this local structure is essential in understanding the properties of optical edge states and light-matter interactions. The global spin is reduced by a factor of 30 in the near field and, for certain frequencies, flipped compared to the pseudospin measured in the far-field. We experimenta…
In quantum wires, such as metallic nanotubes, the optical absorption of the transverse polarization is controlled by the depolarization effect which stems from the redistribution of conduction electrons around the circumference of the system. The traditional electrostatics treatment of the depolarization effect relies on approximating the system by a cylinder with some effective dielectric permittivity. We demonstrate that this simple intuitive picture does not adequately describe optical absorption near its threshold, as the depolarization effect becomes dominated by many-body correlations wh…
Quantum interference in macroscopic crystals of non-metallic Bi$_2$Se$_3$
光电发射实验表明Bi $_2$ Se $_3$是一种拓扑绝缘体。通过控制掺杂,我们获得了具有非金属导电性的Bi $_2$ Se $_3$晶体。在低温下,我们发现了一种新型的磁指纹信号,其中涉及自旋自由度。给定mm尺寸的晶体,观察到的振幅比从普遍电导波动所预期的大200-500 $\times$。结果表明,在这些非金属样品中,在一个不寻常的电导通道中有很长的相位断裂长度。我们讨论了带隙导电态的性质及其与拓扑表面态的关系。
In moiré systems with twisted bilayer graphene (tBLG), the amplification of Coulomb correlation effects at low twist angles ($θ$) is a result of nearly flat low-energy electronic bands and divergent density of states (DOS) at van Hove singularities (vHS). This not only causes superconductivity, Mott insulating states, and quantum anomalous Hall effect close to the critical (or magic) angle $θ= θ_{c} \approx 1.1^\circ$, but also unconventional metallic states that are claimed to exhibit non-Fermi liquid (NFL) excitations. However, unlike superconductivity and the correlation-induced gap in the …
The integer quantum Hall (QH) effects characterized by topologically quantized and nondissipative transport are caused by an electrically insulating incompressible phase that prevents backscattering between chiral metallic channels. We probed the incompressible area susceptible to the breakdown of topological protection using a scanning gate technique incorporating nonequilibrium transport. The obtained pattern revealed the filling-factor ($ν$)-dependent evolution of the microscopic incompressible structures located along the edge and in the bulk region. We found that these specific structures…
Ambipolar surface state transport in non-metallic stoichiometric Bi$_2$Se$_3$ crystals
在Bi $_2$ Se $_3$中实现真正的体绝缘行为,具有简单的单能带电子结构和相当大的带隙的原型拓扑绝缘体,已经被由硒空位引起的众所周知的自掺杂效应所禁止,硒空位的额外电子将化学势移动到体导带中。我们报道了一种新的合成方法,用于实现化学计量比的Bi $_2$ Se $_3$晶体,其在电输运中表现出非金属行为下降到低温。霍尔效应测量表明存在电子和空穴类载流子,后者确定与表面态传导和实现双极运输散装Bi $_2$ Se $_3$晶体没有门控技术。随着载流子迁移率超过最高值尚未报道的拓扑表面状态在这种材料中,通过向上能带弯曲的双极传输的实现被发现提供了一个关键的方法,以提高这种材料的潜力,为未来的研究和应用。
We study the charge and spin dependent scattering in a set of CoFeB thin films whose crystalline order is systematically enhanced and controlled by annealing at increasingly higher temperatures. Terahertz conductivity measurements reveal that charge transport closely follows the development of the crystalline phase, with increasing structural order leading to higher conductivity. The terahertz-induced ultrafast demagnetization, driven by spin-flip scattering mediated by the spin-orbit interaction, is measurable in the pristine amorphous sample and much reduced in the sample with highest crysta…
In conventional Hermitian systems with the open boundary condition, Bloch's theorem is perturbatively broken down, which means although the crystal momentum is not a good quantum number, the eigenstates are the superposition of several extended Bloch waves. In this paper, we show that Bloch's theorem can be non-perturbatively broken down in some Hermitian Bosonic systems. The quasiparticles of the system are the superposition of localized non-Bloch waves, which are characterized by the complex momentum whose imaginary part determines the localization properties. Our work is a Hermitian general…
Evidence for topological surface states in metallic single crystals of Bi2Te3
Bi 2 Te 3是一种被称为拓扑绝缘体的新型材料,其被认为是在本体上绝缘而在表面上导电。然而,由于导电体的存在,表面态的实验验证在电输运测量中一直是困难的。我们报告低温磁输运测量单晶样品的Bi 2 Te 3。我们观察到金属字符在我们的样品和大的线性磁阻从1.5 K到290 K与突出的Shubnikov-de Haas(SdH)振荡,其痕迹持续到20 K。即使我们的样品是金属的,我们也能够获得接近于拓扑表面态的狄拉克费米子所期望的π值的Berry相位。这表明,我们可能已经获得了证据的拓扑表面态的金属单晶Bi 2 Te 3。从SdH振荡的分析中得到的其他物理量也与拓扑表面态的结果非常一致。在我们的样品中观察到的线性磁阻,这被认为是表面态的狄拉克费米子的签名,进一步证明拓扑表面态的存在。
In order to understand the emergence of superconductivity it is useful to study and identify the various pathways leading to the destruction of superconductivity. One way is to use the increase in Coulomb-repulsion due to the increase in disorder, which overpowers the attractive interaction responsible for Cooper-pair formation. A second pathway, applicable to uniformly disordered materials, is the competition between superconductivity and Anderson localization, which leads to electronic granularity in which phase and amplitude fluctuations of the superconducting order parameter play a role. F…
Electrostatics-induced breakdown of the integer quantum Hall effect in cavity QED
JEIP, UAR 3573 CNRS, College de France, PSL Research University(法国学院);SISSA-International School for Advances Studies(国际高等研究学院);ICTP-The Abdus Salam International Centre for Theoretical Physics(阿卜杜斯·萨拉姆国际理论物理中心);Universite Paris-Saclay(巴黎萨克雷大学);Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften(巴伐利亚科学院瓦尔特·迈斯纳研究所);Technische Universität München(慕尼黑工业大学);Munich Center for Quantum Science and Technology (MCQST)(慕尼黑量子科学与技术中心);Istituto Nazionale di Ottica (CNR-INO)(意大利国家光学研究所);European Laboratory for Non-Linear Spectroscopy (LENS)(欧洲非线性光谱学实验室)