Generalized Anderson's theorem for superconductors derived from
**topological** **insulators**

**topological**superconductors have recently displayed unusual robustness against disorder. Here we provide a theoretical framework which naturally explains what protects Cooper pairs from strong scattering in complex superconductors. Our analysis is based on the concept of superconducting fitness and generalizes the famous Anderson's theorem into superconductors having multiple internal degrees of freedom. For concreteness, we report on the extreme example of the Cu$_x$(PbSe)$_5$(Bi$_2$Se$_3$)$_6$ superconductor, where thermal conductivity measurements down to 50 mK not only give unambiguous evidence for the existence of nodes, but also reveal that the energy scale corresponding to the scattering rate is orders of magnitude larger than the superconducting energy gap. This provides a most spectacular case of the generalized Anderson's theorem protecting a nodal superconductor.

9/10 relevant

arXiv

Abundance of $\mathbb{Z}_2$ **topological** order in exfoliable
two-dimensional **insulators**

**insulators**are a class of two-dimensional materials with a finite electronic band gap in the bulk and gapless helical edge states. In the presence of time-reversal symmetry, $\mathbb{Z}_2$

**topological**order distinguishes the

**topological**phase from the ordinary insulating one. Some of the phenomena that can be hosted in these materials, from one-dimensional low-dissipation electronic transport to spin filtering, could be very promising for many technological applications in the fields of electronics, spintronics and

**topological**quantum computing. Nevertheless, the rarity of two-dimensional materials that can exhibit non-trivial $\mathbb{Z}_2$

**topological**order at room temperature hinders development. Here, we screen a comprehensive database we recently created of 1825 monolayers that can be exfoliated from experimentally known compounds, to search for novel quantum spin Hall

**insulators**. Using density-functional and many-body perturbation theory simulations, we identify 13 monolayers that are candidates for quantum spin Hall insulators, including high-performing materials such as AsCuLi$_2$ and jacutingaite (Pt$_2$HgSe$_3$). We also identify monolayer Pd$_2$HgSe$_3$ as a novel Kane-Mele quantum spin Hall insulator, and compare it with jacutingaite. Such a handful of promising materials are mechanically stable and exhibit $\mathbb{Z}_2$

**topological**order, either unpertubed or driven by a small amount of strain. Such screening highlights a relative abundance of $\mathbb{Z}_2$

**topological**order of around 1%, and provides an optimal set of candidates for experimental efforts.

4/10 relevant

arXiv

Crystallographic splitting theorem for band representations and fragile
**topological** photonic crystals

**topological**

**insulators**in class AI are fragile, meaning that the obstruction to symmetric Wannier functions is removable by addition of BRs. An implication of fragility is that its boundary states, while robustly covering the bulk energy gap in finite-rank tight-binding models, are unstable if the Hilbert space is expanded to include all symmetry-allowed representations. These fragile

**insulators**have photonic analogs that we identify; in particular, we prove that an existing photonic crystal built by Yang et al. [Nature 565, 622 (2019)] is fragile

**topological**with removable surface states, which disproves a widespread perception of `topologically-protected' surface states in time-reversal-invariant, gapped photonic/phononic crystals. Our theorem is finally applied to derive various symmetry obstructions on the Wannier functions of

**topological**insulators, and to prove their equivalence with the nontrivial holonomy of Bloch functions.

6/10 relevant

arXiv

Theory of bi-linear magnetoresistance within the minimal model for
surface states in **topological** **insulators**

**topological**

**insulators**(TIs). Expand abstract.

**topological**

**insulators**(TIs). The BMR appears as a consequence of the second-order response to electric field, and depends linearly on both electric field (current) and magnetic field. The mechanism is based on the interplay of current-induced spin polarization and scattering processes due to peculiar spin-orbit defects. The proposed mechanism is compared to that based on a Fermi surface warping, and is shown to be dominant at lower Fermi energies. We provide a consistent theoretical approach based on the Green function formalism and show that the magnetic field dependent relaxation processes in the presence of non-equilibrium current-induced spin polarization give rise to the BMR.

10/10 relevant

arXiv

Exciting Pseudospin Dependent Edge States in Plasmonic Metasurfaces

**topological**

**insulators**, these modes are not purely unidirectional and their propagation properties can be understood by analysing the spin angular momentum of the electromagnetic field, which is inhomogenous in the plane of the lattice. Expand abstract.

**topological**

**insulators**. However, unlike the spin-momentum locking characteristic of

**topological**insulators, these modes are not purely unidirectional and their propagation properties can be understood by analysing the spin angular momentum of the electromagnetic field, which is inhomogenous in the plane of the lattice. The local sign of the spin angular momentum determines the propagation direction of the mode under a near-field excitation source. We also study the optical response under far-field excitation and discuss in detail the effects of radiation and retardation.

5/10 relevant

arXiv

Universal momentum-to-real-space mapping of **topological** singularities

**Topological**properties of materials, as manifested in the intriguing phenomena of quantum Hall effect and

**topologic**al

**insulators**, have attracted overwhelming transdisciplinary interest in recent years. Expand abstract.

**Topological**properties of materials, as manifested in the intriguing phenomena of quantum Hall effect and

**topological**insulators, have attracted overwhelming transdisciplinary interest in recent years.

**Topological**edge states, for instance, have been realized in versatile systems including electromagnetic-waves. Typically,

**topological**properties are revealed in momentum space, using concepts such as Chern number and Berry phase. Here, we demonstrate a universal mapping of the topology of Dirac-like cones from momentum space to real space. We evince the mapping by exciting the cones in photonic honeycomb (pseudospin-1/2) and Lieb (pseudospin-1) lattices with vortex beams of

**topological**charge l, optimally aligned for a chosen pseudospin state s, leading to direct observation of

**topological**charge conversion that follows the rule of l to l+2s. The mapping is theoretically accounted for all initial excitation conditions with the pseudospin-orbit interaction and nontrivial Berry phases. Surprisingly, such a mapping exists even in a deformed lattice where the total angular momentum is not conserved, unveiling its

**topological**origin. The universality of the mapping extends beyond the photonic platform and 2D lattices: equivalent

**topological**conversion occurs for 3D Dirac-Weyl synthetic magnetic monopoles, which could be realized in ultracold atomic gases and responsible for mechanism behind the vortex creation in electron beams traversing a magnetic monopole field.

4/10 relevant

arXiv

Bound states in the continuum of higher-order **topological** **insulators**

**topological**bulk-boundary correspondences are immune to the existence of interfering bulk bands, expanding the search space for crystalline

**topologic**al phases. Expand abstract.

**Topological**bound states in these phases thus constitute condensed matter realizations of bound states in the continuum (BICs). We propose a method for the direct identification of BICs in condensed matter settings and use it to demonstrate the existence of BICs in a concrete lattice model. Although the onset for these states is given by corner-induced filling anomalies in certain

**topological**crystalline phases, additional symmetries are required to protect the BICs from hybridizing with their degenerate bulk states. We analytically demonstrate the protection mechanism for BICs in this model and numerically show how breaking this mechanism transforms the BICs into resonances. Our work shows that

**topological**bulk-boundary correspondences are immune to the existence of interfering bulk bands, expanding the search space for crystalline

**topological**phases.

8/10 relevant

arXiv

Probing the minigap in **topological** **insulator**-based Josephson junctions
under radio frequency irradiation

**topological**

**insulators**(3D TIs). Expand abstract.

**topological**

**insulators**(3D TIs). In this work, we further generalize that method to the circumstance with radio frequency (rf) irradiation. We find that with the increase of rf power, the measured minigap becomes broadened and extends to higher energies, in a way similar to the rf power dependence of the outer border of the Shapiro step region. We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction model (RSJ model) and the Blonder-Tinkham-Klapwijk (BTK) theory. Our findings could be useful when using the contact-resistance-measurement method to study the Majorana-related physics in

**topological**

**insulator**-based Josephson junctions under rf irradiation.

10/10 relevant

arXiv

Radiative Decay of Bound Electron Pairs in Two-Dimensional **Topological**
**Insulators**

**topological**

**insulators**. The decay time is found to be rather large on the scale of the characteristic relaxation times of the electron system and significantly dependent on the

**topological**properties and dispersion of the band states. In

**topological**phase the decay time is much longer than in the trivial one, and is estimated as $\sim$1~ns for the HgTe/CdHgTe heterostructures. However, the longest decay time is in the

**topological**phase with nearly flat dispersion in the band extema.

10/10 relevant

arXiv

Quantum decay in a **topological** continuum

**topological**

**insulators**, and show that the chiral nature of scattering states fully suppresses Fano interference among overlapping resonances. Expand abstract.

**topological**insulators, and show that the chiral nature of scattering states fully suppresses Fano interference among overlapping resonances. As a result, there are not bound states in the continuum, quantum decay is complete, and there is not any signature of particle statistics in the decay process. Nonetheless, some interesting features are disclosed in the multilevel decay dynamics in a

**topological**bath, such as the appearance of high-order exceptional points, long quiescent dynamics followed by a fast decay, and the possibility to observe damped non-Hermitian Bloch oscillations.

4/10 relevant

arXiv