Measuring the Berry phase of graphene from wavefront dislocations in Friedel oscillations

Dutreix, C.; González‐Herrero, Héctor; Brihuega, I.; Katsnelson, M. I.; Chapelier, Claude; Renard, V.

doi:10.1038/s41586-019-1613-5

Cited by 65 publications

(80 citation statements)

References 37 publications

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“…In two dimensions, examples include the sublattice degree of freedom for graphene and the spin-angular momentum (SAM) for the surface states in topological insulators (TI). Accordingly, the nontrivial Berry-phase properties have been addressed by quasiparticle interference STM imaging and dichroic ARPES in graphene 20 , 21 and by spin-resolved ARPES in TI 22 . Likewise in 3D WSM, one may expect the relevant degrees of freedom to depend on the considered material system.…”

Section: Introductionmentioning

confidence: 99%

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

Ünzelmann¹,

Bentmann²,

Figgemeier³

et al. 2021

Nat Commun

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Since the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids.

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Section: Introductionmentioning

confidence: 99%

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

Ünzelmann¹,

Bentmann²,

Figgemeier³

et al. 2021

Nat Commun

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show abstract

“…Now we show that the change of N A observed in the LDOS maps arises as a ubiquitous wave phenomenon and is the signature of a wavefront dislocation in the LDOS. Topological defects in waves rely on generic assumptions that do not involve the wave equation, and so they are ubiquitously involved in branches of physics as various as electromagnetism, optics, acoustics, fluid physics, astrophysics, and condensed matter physics [2][3][4][5][6][7][8]10,11,40,41 . The wavefront dislocations are associated with the topological phase singularities of wavefields in a space of at least dimension 2.…”

Section: Resultsmentioning

confidence: 99%

“…However, these are usually well resolved from the LDOS in Fourier space, where the topological scattering phase can be resolved too 34 , 40 . Such a Fourier analysis is what enabled recent experiments to extract real-space wavefront dislocations as manifestation of topological semimetals with non-monotonic dispersion relations 10 , 11 .…”

Section: Discussionmentioning

confidence: 99%

“…Wavefront dislocations have been observed from the physics of fluids, sound, electromagnetism to oceanic tides and astronomy, and even led to the birth of a whole research field known as singular optics [2][3][4][5][6][7] . In quantum mechanics, wavefront dislocations have been predicted in connection to the Aharonov-Bohm effect 8,9 , and they have been observed recently in the electron density of graphene as a manifestation of the wave-function Berry phase 10,11 . In parallel, topology also spread in condensed matter physics, giving rise to the field of topological phases of matter 12,13 and its various classical analogues such as topological photonics 14 .…”

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confidence: 99%

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Wavefront dislocations reveal the topology of quasi-1D photonic insulators

Dutreix

Bellec

Delplace³

et al. 2021

Nat Commun

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Phase singularities appear ubiquitously in wavefields, regardless of the wave equation. Such topological defects can lead to wavefront dislocations, as observed in a humongous number of classical wave experiments. Phase singularities of wave functions are also at the heart of the topological classification of the gapped phases of matter. Despite identical singular features, topological insulators and topological defects in waves remain two distinct fields. Realising 1D microwave insulators, we experimentally observe a wavefront dislocation – a 2D phase singularity – in the local density of states when the systems undergo a topological phase transition. We show theoretically that the change in the number of interference fringes at the transition reveals the topological index that characterises the band topology in the insulator.

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“…To support this explanation, we further describe the impurity scattering of the massless relativistic electrons within a T -matrix approach based on Green functions [31]. This diagrammatic perturbation approach leads to an analytical solution for on-site potentials, regardless of the potential strength.…”

Section: The Dislocation Strength Is a Measure Of The Berry Phasementioning

confidence: 98%

Measuring graphene’s Berry phase at B=0 T

Dutreix¹,

González‐Herrero²,

Brihuega³

et al. 2022

Comptes Rendus. Physique

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The Berry phase of wave functions is a key quantity to understand various low-energy properties of matter, among which electric polarisation, orbital magnetism, as well as topological and ultra-relativistic phenomena. Standard approaches to probe the Berry phase in solids rely on the electron dynamics in response to electromagnetic forces. In graphene, probing the Berry phase π of the massless relativistic electrons requires an external magnetic field. Here, we show that the Berry phase also affects the static response of the electrons to a single atomic scatterer, through wavefront dislocations in the surrounding standing-wave interference. This provides a new experimental method to measure the graphene Berry phase in the absence of any magnetic field and demonstrates that local disorder can be exploited as probe of topological quantum matter in scanning tunnelling microscopy experiments.

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Measuring the Berry phase of graphene from wavefront dislocations in Friedel oscillations

Cited by 65 publications

References 37 publications

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs

Wavefront dislocations reveal the topology of quasi-1D photonic insulators

Measuring graphene’s Berry phase at B=0 T

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