We demonstrate a non-Hermitian topological effect that is characterized by having complex eigenvalues only in the edge states of a topological material, despite the fact that the material is completely uniform. Such an effect can be constructed in any topological structure formed by two gapped subsystems, e.g., a quantum spin-Hall system, with a suitable non-Hermitian coupling between the spins. The resulting complex-eigenvalued edge state is robust against defects due to the topological protection. In photonics, such an effect can be used for the implementation of topological lasers, in which a uniform pumping provides gain only in the edge lasing state. Furthermore, such a topological lasing model is reciprocal and is thus compatible with standard photonic platforms.

In crystals, two bands may cross each other and form degeneracies along a closed loop in the three-dimensional momentum space, which is called nodal line. Nodal line degeneracy can be designed to exhibit various configurations such as nodal rings, chains, links, and knots. Very recently, non-Abelian band topology was proposed in nodal link systems, where the nodal lines formed by consecutive pairs of bands exhibit interesting braiding structures and the underlying topological charges are described by quaternions. Here, we experimentally demonstrate non-Abelian nodal links in a biaxial hyperbolic metamaterial. The linked nodal lines threading through each other are formed by the crossings between three adjacent bands. Based on the non-Abelian charges, we further analyze various admissible nodal link configurations for the three-band system. On the interface between the metamaterial and air, surface bound states in the continuum are observed, which serves as the symmetry-enforced derivative of drumhead surface states from the linked nodal lines. Our work serves as a direct observation of the global topological structures of nodal links, and provides a platform for studying non-Abelian topological charge in the momentum space.

We develop a theory for the interaction of light with superfluid optical media, describing the motion of quantum impurities that are created and dragged through the liquid by propagating photons. It is well known that a mobile impurity suffers dissipation due to phonon emission as soon as it moves faster than the speed of sound in the superfluid—Landau’s critical velocity. Surprisingly we find that in the present hybrid light-matter setting, polaritonic impurities can be protected against environmental decoherence and be allowed to propagate well above the Landau velocity without jeopardizing the superfluid response of the medium.

A sufficiently large perpendicular magnetic field quenches the kinetic (Fermi) energy of an interacting two-dimensional (2D) system of fermions, making them susceptible to the formation of a Wigner solid (WS) phase in which the charged carriers organize themselves in a periodic array in order to minimize their Coulomb repulsion energy. In low-disorder 2D electron systems confined to modulation-doped GaAs heterostructures, signatures of a magnetic-field-induced WS appear at low temperatures and very small Landau level filling factors ($\nu \simeq 1/5$). In dilute GaAs 2D hole systems, on the other hand, thanks to the larger hole effective mass and the ensuing Landau level mixing, the WS forms at relatively higher fillings ($\nu \simeq 1/3$). Here we report our measurements of the fundamental temperature vs filling phase diagram for the 2D holes’ WS-liquid thermal melting. Moreover, via changing the 2D hole density, we also probe their Landau level mixing vs filling WS-liquid quantum melting phase diagram. We find our data to be in good agreement with the results of very recent calculations, although intriguing subtleties remain.

We show that topological defects in an ion-doped nematic liquid crystal can be used to manipulate the surface charge distribution on chemically homogeneous, charge-regulating external surfaces, using a minimal theoretical model. In particular, the location and type of the defect encodes the precise distribution of surface charges and the effect is enhanced when the liquid crystal is flexoelectric. We demonstrate the principle for patterned surfaces and charged colloidal spheres. More generally, our results indicate an interesting approach to control surface charges on external surfaces without changing the surface chemistry.

Decades of precision measurements have firmly established the Kobayashi-Maskawa phase as the dominant source of the charge-parity ($CP$) violation observed in weak quark decays. However, it is still unclear whether $CP$ violation is explicitly encoded in complex Yukawa matrices or instead stems from spontaneous symmetry breaking with underlying $CP$-conserving Yukawa and Higgs sectors. Here we study the latter possibility for the case of a generic two-Higgs-doublet model. We find that theoretical constraints limit the ratio $t_{\beta }$ of the vacuum expectation values (vevs) to the range $0.22\le t_{\beta }\le 4.5$ and imply the upper bounds $M_{H^{\pm }}\le 435\mathrm{GeV}$, $M_{H_2^0}\le 485\mathrm{GeV}$ and $M_{H_3^0}\le 545\mathrm{GeV}$ for the charged and extra neutral Higgs masses. We derive lower bounds on charged-Higgs couplings to bottom quarks which provide a strong motivation to study the nonstandard production and decay signatures $pp\to qb{H}^{\pm }(\to q^{\prime }b)$ with all flavors $q,q^{\prime }=u$, $c$, $t$ in the search for the charged Higgs boson. We further present a few benchmark scenarios with interesting discovery potential in collider analyses.

When Th nuclei are doped in ${\mathrm{CaF}}_2$ crystals, a set of electronic defect states appear in the crystal band gap which would otherwise provide complete transparency to vacuum-ultraviolet radiation. The coupling of these defect states to the 8 eV ${}^{229m}\mathrm{Th}$ nuclear isomer in the ${\mathrm{CaF}}_2$ crystal is investigated theoretically. We show that although previously viewed as a nuisance, the defect states provide a starting point for nuclear excitation via electronic bridge mechanisms involving stimulated emission or absorption using an optical laser. The rates of these processes are at least 2 orders of magnitude larger than direct photoexcitation of the isomeric state using available light sources. The nuclear isomer population can also undergo quenching when triggered by the reverse mechanism, leading to a fast and controlled decay via the electronic shell. These findings are relevant for a possible solid-state nuclear clock based on the ${}^{229m}\mathrm{Th}$ isomeric transition.

A new, very short-lived neutron-deficient isotope ${}^{222}\mathrm{Np}$ was produced in the complete-fusion reaction ${}^{187}\mathrm{Re}({}^{40}\mathrm{Ar},5\mathrm{n}){}^{222}\mathrm{Np}$, and observed at the gas-filled recoil separator SHANS. The new isotope ${}^{222}\mathrm{Np}$ was identified by employing a recoil-$\alpha$ correlation measurement, and six $\alpha$-decay chains were established for it. The decay properties of ${}^{222}\mathrm{Np}$ with $E_{\alpha }=10016(33)\mathrm{keV}$ and $T_{1/2}=380_{-110}^{+260}\mathrm{ns}$ were determined experimentally. The $\alpha$-decay systematics of Np isotopes is improved by adding the new data for ${}^{222}\mathrm{Np}$, which validates the $N=126$ shell effect in Np isotopes. The evolution of the $N=126$ shell closure is discussed in the neutron-deficient nuclei up to Np within the framework of $\alpha$-decay reduced width.

We study a noisy oscillator with pulse delayed feedback, theoretically and in an electronic experimental implementation. Without noise, this system has multiple stable periodic regimes. We consider two types of noise: (i) phase noise acting on the oscillator state variable and (ii) stochastic fluctuations of the coupling delay. For both types of stochastic perturbations the system hops between the deterministic regimes, but it shows dramatically different scaling properties for different types of noise. The robustness to conventional phase noise increases with coupling strength. However for stochastic variations in the coupling delay, the lifetimes decrease exponentially with the coupling strength. We provide an analytic explanation for these scaling properties in a linearized model. Our findings thus indicate that the robustness of a system to stochastic perturbations strongly depends on the nature of these perturbations.

We examine the dynamics of small anisotropic particles (spheroids) sedimenting through homogeneous isotropic turbulence using direct numerical simulations and theory. The gravity-induced inertial torque acting on sub-Kolmogorov spheroids leads to pronouncedly non-Gaussian orientation distributions localized about the broadside-on (to gravity) orientation. Orientation distributions and average settling velocities are obtained over a wide range of spheroid aspect ratios, Stokes, and Froude numbers. Orientational moments from the simulations compare well with analytical predictions in the inertialess rapid-settling limit, with both exhibiting a nonmonotonic dependence on spheroid aspect ratio. Deviations arise at Stokes numbers of order unity due to a spatially inhomogeneous particle concentration field resulting from a preferential sweeping effect; as a consequence, the time-averaged particle settling velocities exceed the orientationally averaged estimates.

We numerically demonstrate that the topological corner states residing in the corners of higher-order topological insulator possess non-Abelian braiding properties. Such topological corner states are Dirac fermionic modes other than Majorana zero modes. We claim that Dirac fermionic modes protected by nontrivial topology also support non-Abelian braiding. An analytical description on such non-Abelian braiding is conducted based on the vortex-induced Dirac-type fermionic modes. Finally, the braiding operators for Dirac fermionic modes, especially their explicit matrix forms, are analytically derived and compared with the case of Majorana zero modes.

Doping a two-dimensional semiconductor with magnetic atoms is a possible route to induce magnetism in the material. We report on the atomic structure and electronic properties of monolayer ${\mathrm{WSe}}_2$ intentionally doped with vanadium atoms by means of scanning transmission electron microscopy and scanning tunneling microscopy and spectroscopy. Most of the V atoms incorporate at W sites. These ${\mathrm{V}}_W$ dopants are negatively charged, which induces a localized bound state located 140 meV above the valence band maximum. The overlap of the electronic potential of two charged ${\mathrm{V}}_W$ dopants generates additional in-gap states. Eventually, the negative charge may suppress the magnetic moment on the ${\mathrm{V}}_W$ dopants.

Defects have been known to substantially affect quantum states of materials including charge density wave (CDW). However, the microscopic mechanism of the influence of defects is often elusive due partly to the lack of atomic scale characterization of defects themselves. We investigate native defects of a prototypical CDW material $2H\text{−}{\mathrm{NbSe}}_2$ and their microscopic interaction with CDW. Three prevailing types of atomic scale defects are classified by scanning tunneling microscope, and their atomic structures are identified by density functional theory calculations as Se vacancies and Nb intercalants. Above the transition temperature, two distinct CDW structures are found to be induced selectively by different types of defects. This intriguing phenomenon is explained by competing CDW ground states and local lattice strain fields induced by defects, providing a clear microscopic mechanism of the defect-CDW interaction.

Here, we present microscopic evidence of the persistence of uniaxial $A$-type antiferromagnetic order to the surface layers of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ single crystals using magnetic force microscopy. Our results reveal termination-dependent magnetic contrast across both surface step edges and domain walls, which can be screened by thin layers of soft magnetism. The robust surface $A$-type order is further corroborated by the observation of termination-dependent surface spin-flop transitions, which have been theoretically proposed decades ago. Our results not only provide key ingredients for understanding the electronic properties of the antiferromagnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, but also open a new paradigm for exploring intrinsic surface metamagnetic transitions in natural antiferromagnets.

Using first-principles approaches we find that the Auger recombination in PbSe is anomalous in three distinct ways. First, the direct Auger coefficient is 4 orders of magnitude lower than that of other semiconductors with similar band gaps, a result that can be attributed to the lack of involvement of a heavy-hole band. Second, phonon-assisted indirect Auger recombination prevails, contrary to the common belief that direct Auger is dominant in narrow-gap semiconductors. Third, an unexpectedly weak temperature dependence of the Auger coefficient is observed, which we can now attribute to the indirect nature of the Auger process. The widely accepted explanation of this behavior in terms of an unusual temperature dependence of the band gap is only a secondary effect. Our results elucidate the mechanisms underlying the anomalous Auger recombination in IV-VI semiconductors in general, which is critical for understanding and engineering carrier transport.

Extensive numerical simulations in the past decades proved that the critical exponents of the jamming of frictionless spherical particles are the same in two and three dimensions. This implies that the upper critical dimension is $d_u=2$ or lower. In this Letter, we study the jamming transition below the upper critical dimension. We investigate a quasi-one-dimensional system: disks confined in a narrow channel. We show that the system is isostatic at the jamming transition point as in the case of standard jamming transition of the bulk systems in two and three dimensions. Nevertheless, the scaling of the excess contact number shows the linear scaling. Furthermore, the gap distribution remains finite even at the jamming transition point. These results are qualitatively different from those of the bulk systems in two and three dimensions.

We analyze and experimentally demonstrate quantum steering using criteria based on generalized entropies and criteria with minimal assumptions based on the so-called dimension-bounded steering. Further, we investigate and compare their robustness against experimental imperfections such as misalignment in the shared measurement reference frame. While entropy based criteria are robust against imperfections in state preparation, we demonstrate an advantage in dimension-bounded steering in the presence of measurement imprecision. As steering with such minimal assumptions is easier to reach than fully nonlocal correlations, and as our setting requires very little trust in the measurement devices, the results provide a candidate for the costly Bell tests while remaining highly device independent.