The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.

The Zak phase γ, the generalization of the Berry phase to Bloch wave functions in solids, is often used to characterize inversion-symmetric 1D topological insulators; however, since its value can depend on the choice of real-space origin and unit cell, only the difference between the Zak phase of two regions is believed to be relevant. Here, we show that one can extract an origin-independent part of γ, the so-called inter-cellular Zak phase γ inter , which can be used as a bulk quantity to predict the number of surface modes as follows: a neutral finite 1D tight-binding system has ns = γ inter /π (mod 2) number of in-gap surface modes below the Fermi level if there exists a commensurate bulk unit cell that respects inversion symmetry. We demonstrate this by first verifying that ±eγ inter /2π (mod e) is equal to the extra charge accumulation in the surface region for a general translationally invariant 1D insulator, while the remnant part of γ, the intra-cellular Zak phase γ intra , corresponds to the electronic part of the dipole moment of the bulk's unit cell. Second, we show that the extra charge accumulation can be related to the number of surface modes when the unit cell is inversion symmetric. This bulk-boundary correspondence using γ inter reduces to the conventional one using γ when the real-space origin is at the inversion center. Our work thereby clarifies the usage of γ in the bulk-boundary correspondence. We study several tight binding models to quantitatively check the relation between the extra charge accumulation and the inter-cellular Zak phase as well as the bulk-boundary correspondence using the inter-cellular Zak phase.

Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly-rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two white dwarfs complete a final merger on a dynamical timescale, and are tidally disrupted, producing a rapidly-rotating white dwarf merger surrounded by a hot corona and a thick, differentially-rotating disk. The disk is strongly susceptible to the magnetorotational instability (MRI), and we demonstrate that this leads to the rapid growth of an initially dynamically weak magnetic field in the disk, the spin-down of the white dwarf merger, and to the subsequent central ignition of the white dwarf merger. Additionally, these magnetized models exhibit new features not present in prior hydrodynamic studies of white dwarf mergers, including the development of MRI turbulence in the hot disk, magnetized outflows carrying a significant fraction of the disk mass, and the magnetization of the white dwarf merger to field strengths ∼ 2 × 10 8 G. We discuss the impact of our findings on the origins, circumstellar media, and observed properties of SNe Ia and magnetized white dwarfs.

Quantum anomalies are the breaking of a classical symmetry by quantum fluctuations. They dictate how physical systems of diverse nature, ranging from fundamental particles to crystalline materials, respond topologically to external perturbations, insensitive to local details. The anomaly paradigm was triggered by the discovery of the chiral anomaly that contributes to the decay of pions into photons and influences the motion of superfluid vortices in 3 He-A. In the solid state, it also fundamentally affects the properties of topological Weyl and Dirac semimetals, recently realized experimentally. In this work we propose that the most identifying consequence of the chiral anomaly, the charge density imbalance between fermions of different chirality induced by nonorthogonal electric and magnetic fields, can be directly observed in these materials with the existing technology of photoemission spectroscopy. With angle resolution, the chiral anomaly is identified by a characteristic note-shaped pattern of the emission spectra, originating from the imbalanced occupation of the bulk states and a previously unreported momentum dependent energy shift of the surface state Fermi arcs. We further demonstrate that the chiral anomaly likewise leaves an imprint in angle averaged emission spectra, facilitating its experimental detection. Thereby, our work provides essential theoretical input to foster the direct visualization of the chiral anomaly in condensed matter, in contrast to transport properties, such as negative magnetoresistance, which can also be obtained in the absence of a chiral anomaly.

Condensed matter systems realizing Weyl fermions exhibit striking phenomenology derived from their topologically protected surface states as well as chiral anomalies induced by electromagnetic fields. More recently, inhomogeneous strain or magnetization were predicted to result in chiral electric E5 and magnetic B5 fields, which modify and enrich the chiral anomaly with additional terms. In this work we develop a lattice-based approach to describe the chiral anomaly, which involves Landau and pseudo-Landau levels and treats all anomalous terms on equal footing, while naturally incorporating Fermi arcs. We exemplify its potential by physically interpreting the largely overlooked role of Fermi arcs in the covariant (Fermi level) contribution to the anomaly and revisiting the factor of 1/3 difference between the covariant and consistent (complete band) contributions to the E5·B5 term in the anomaly. Our framework provides a versatile tool for the analysis of anomalies in realistic lattice models as well as a source of simple physical intuition for understanding strained and magnetized inhomogeneous Weyl semimetals.Quantum anomalies describe the breaking of a classical symmetry by quantum fluctuations [1]. The chiral anomaly, the nonconservation of the chiral charge of three-dimensional Weyl fermions, is relevant to different domains in physics since Weyl fermions mediate the pion-decay into photons [2,3] and are emergent quasiparticles in Weyl semimetals [4][5][6][7][8][9]. The physics is particularly transparent in the Landau level picture pioneered by Nielsen and Ninomiya [10], requiring only basic quantum mechanics. In a magnetic field B, the conical Weyl dispersion evolves into Landau levels with a degeneracy proportional to |B| [10]. Since momentum along the direction of the magnetic field remains a good quantum number, the Landau levels disperse in that direction, with the zeroth Landau level having a linear dispersion with a sign determined by the chirality; all other Landau levels have a quadratic dispersion. The zeroth Landau level of the left-and right-handed Weyl fermions furthermore connect at high energy. Consequently, an electric field (E) with a component along the dispersion transfers lefthanded fermions to right-handed fermions (or vice versa) resulting in a nonconservation of left and right particle numbers proportional to E · B [1, 10, 11].Other fields, such as chiral pseudo-electromagnetic fields, torsion or curvature activate the chiral anomaly beyond E and B [12][13][14][15][16][17][18][19][20][21][22]. Weyl semimetals are ideal to probe the chiral anomaly in the presence of chiral pseudoelectromagnetic fields. To motivate this, recall that their low-energy degrees of freedom are pairs of chiral Weyl quasiparticles at topologically protected band touchings (Weyl nodes), separated in energy-momentum space by a four-vector b µ [9]. A space-and time-dependent b µ , as in strained or inhomogenously magnetized Weyl semimetals [15] or 24], generates chiral pseudomagnetic (B 5 = ∇×b) and pseudoelectri...