拓扑绝缘体表面形变引起的测地散射

Experimental realization of two-dimensional weak topological insulators

We report the experimental realization of two-dimensional (2D) weak topological insulator (WTI) in spinless Su-Schrieffer-Heeger circuits with parity-time and chiral symmetries. Strong and weak $\mathbb{Z}_2$ topological indexes are adopted to explain the experimental findings that a Dirac semimetal (DSM) phase and four WTI phases emerge in turn when we modulate the centrosymmetric circuit deformations. In DSM phase, it is found that the Dirac cone is highly anisotropic and not pinned to any high-symmetry points but can widely move within the Brillouin zone, which eventually leads to the phase…

Viscoelastic response of topological tight-binding models in two and three dimensions

The topological response to external perturbations is an effective probe to characterize different topological phases of matter. Besides the Hall conductance, the Hall viscosity is another example of such a response that measures how electronic wave functions respond to changes in the underlying geometry. Topological (Chern) insulators are known to have a quantized Hall conductance. A natural question is how the Hall viscosity behaves for these materials. So far, most of studies on the Hall viscosity of Chern insulators have focused on the continuum limit. The presence of lattice breaks the co…

拓扑绝缘体的扭转响应和无耗散粘性

Torsional Response and Dissipationless Viscosity in Topological Insulators

我们考虑了二维和三维拓扑绝缘体（TI）中电子自由度的粘弹性响应。我们的主要重点是在2D陈省身绝缘体表现出大量dissipationless粘度类似于量子霍尔粘度预测整数和分数量子霍尔状态。我们表明，无耗散粘度是一个TI的基本晶格几何形状的扭转变形的响应。粘弹性响应还表明，晶体位错在陈绝缘体将携带动量密度。我们简要地讨论了3D的概括，这意味着时间反演不变TI的将表现出量子霍尔粘度在其表面上。

Topological gap states of semiconducting armchair graphene ribbons

In semiconducting armchair graphene ribbons a chiral lattice deformation can induce pairs of topological gap states with opposite energies. Near the critical value of the deformation potential these kink and antikink states become almost degenerate with zero energy and have a fractional charge one-half. Such a semiconducting armchair ribbon represents a one-dimensional topological insulator with nearly zero energy end states. Using data collapse of numerical results we find that the shape of the kink displays an anomalous power-law dependence on the width of the local lattice deformation. We s…

Pressure-Induced Insulator-to-Metal Transition Provides Evidence for Negative-$U$ Centers in Large-Gap Disordered Insulators

Attractive negative-$U$ interactions between electrons facilitated by strong electron-phonon interaction are common in highly polarizable and disordered materials such as amorphous chalcogenides, but there is no direct evidence for them in large-band-gap insulators. Here we report how such negative-$U$ centers are responsible for widespread insulator-to-metal transitions in amorphous HfO$_2$ and Al$_2$O$_3$ thin films with a 10$^9$-fold resistance drop. Triggered by a static hydraulic pressure or a 0.1 ps impulse of magnetic pressure, the transition can proceed at such low pressure that there …

应变工程法研究石墨烯的能隙、拓扑绝缘体态和零场量子霍尔效应

Energy gaps, topological insulator state and zero-field quantum Hall effect in graphene by strain engineering

在石墨烯的许多显著品质中，由于电荷载流子的无质量手性特性，其电子性质引起了特别的兴趣，这导致了即使在室温下也可观察到的不寻常现象，如无载流子极限下的金属导电性和半整数量子霍尔效应（QHE）[1 - 3]。因为石墨烯只有一个原子厚，它也容易受到包括机械变形在内的外部影响。后者提供了通过应变控制石墨烯性质的诱人前景，并且最近，一些报告已经研究了单轴变形下的石墨烯[4 - 8]。虽然应变可以诱导额外的拉曼特征[7，8]，但对于约1000 μ m的实际应变，没有观察到或预期石墨烯的能带结构发生显著变化。10%[9 - 11]。在这里，我们表明，沿三个主要晶体学方向排列的设计应变诱导强规范场[12 - 14]，其有效地充当超过10 T的均匀磁场。对于有限掺杂，量子化场导致绝缘体和一对反循环边缘态，类似于拓扑绝缘体的情况[15 - 20]。我们提出了创造这种量子态和观察赝磁QHE的现实方法。我们还表明，应变超晶格可以用来打开石墨烯的电子光谱中的显着的能隙。

Topolectrical-circuit octupole insulator with topologically protected corner states

Recent theoretical studies have extended the Berry phase framework to account for higher electric multipole moments, quadrupole and octupole topological phases have been proposed. Although the two-dimensional quantized quadrupole insulators have been demonstrated experimentally, octupole topological phases have not previously been observed experimentally. Here we report on the experimental realization of classical analog of octupole topological insulator in the electric circuit system. Three-dimensional topolectrical circuits for realizing such topological phases are constructed experimentally…