Signatures of Dirac fermion-mediated magnetic order

Sessi, Paolo; Reis, Felix; Bathon, Thomas; Кох, К. А.; Tereshchenko, O. E.; Bode, Matthias

doi:10.1038/ncomms6349

Cited by 74 publications

(103 citation statements)

References 44 publications

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“…Recently, it has been further expanded to study spin-split surface states on surface alloys 10 and topological insulators 11,12 . QPI has proven to be a powerful method to analyse electronic properties, such as energy dispersion relations 13 , lifetimes [14][15][16] , scattering phase shifts 1,7 , coherence lengths 9 and scattering channels 10,11,12 . One of the fundamental aspects of the QPI mapping is that in real space the amplitude of the LDOS oscillations reduces as the tip is moved away from the scattering centres.…”

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Direct observation of many-body charge density oscillations in a two-dimensional electron gas

et al. 2015

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Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an 'anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale.

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Direct observation of many-body charge density oscillations in a two-dimensional electron gas

et al. 2015

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“…Their appearance implies an active role of the time-reversal symmetry breaking perturbations, i.e. the Mn adatoms, which, following theoretical predictions [15], we recently suggested to be magnetically coupled by the Dirac fermions present on the TI surface [12] (see XMCD discussion below).…”

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Superparamagnetism-induced mesoscopic electron focusing in topological insulators

et al. 2016

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1 arXiv:1602.03902v1 [cond-mat.mes-hall] 11 Feb 2016 AbstractThe particle-wave duality sets a fundamental correspondence between optics and quantum mechanics. Within this framework, the propagation of quasiparticles can give rise to superposition phenomena which, like for electromagnetic waves, can be described by the Huygens principle. However, the utilization of this principle by means of propagation and manipulation of quantum information is limited by the required coherence in time and space. Here we show that in topological insulators, which in their pristine form are characterized by opposite propagation directions for the two quasiparticles spin channels, mesoscopic focusing of coherent charge density oscillations can be obtained at large nested segments of constant-energy contours by magnetic surface doping. Our findings provide evidence of strongly anisotropic Dirac fermion-mediated interactions. Even more remarkably, the validity of our findings goes beyond topological insulators but applies for systems with spin-orbit-lifted degeneracy in general. It demonstrates how spin information can be transmitted over long distances, allowing the design of experiments and devices based on coherent quantum effects in this fascinating class of materials. 2Coherence is a general property of waves as it describes the capability of keeping a welldefined phase relation while propagating in space and time. Because of the particle-wave duality, which lays at the very foundations of quantum mechanics, the same concept can also be applied to quasiparticles in solids. Quantum coherence is of fundamental importance since it sets the limits up to which information can be transmitted and processed with high fidelity. With the invention of the scanning tunneling microscope it became possible to visualize coherent phenomena in real space by imaging the standing wave pattern produced by scattering events around individual atomic-scale defects [1]. In analogy with electromagnetic waves these results can be interpreted within the Huygens principle. It describes the interference pattern which results from the superposition of waves propagating along all different paths and can be theoretically elegantly expressed by using the quantum-mechanical propagator.The further development of atomic-scale manipulation techniques allowed to engineer these properties at the atomic scale. This capability was used for the creation of exotic effects such as quantum mirages [2], for the extraction of the phase of electron wave functions to analyze how propagating waves in solids are influenced by the periodic potential of the crystal lattice. In particular, it has been shown that the propagation of quasiparticle waves can become anisotropic when the shape of a constant-energy cut (CEC) deviates from an isotropic contour. In analogy to optics, focussing and defocussing lead to an enhanced intensity along certain crystallographic directions and to partial or even complete suppression along others, respectively [5]. However, despite its relevance in s...

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“…This technique makes use of the standing-wave pattern generated by elastic scattering of electronic states at surface defects and has been proven to be a powerful method to test the properties of topological materials [38][39][40][41][42][43]. Contrary to conventional photoemission spectroscopy, it gives access to both occupied and unoccupied electronic states thereby providing a complete spectroscopic characterization of all relevant electronic features around the Fermi energy.…”

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confidence: 99%