| 1. |
- Balatsky, Alexander V., et al.
(författare)
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Dynamic Quantum Matter
- 2020
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Ingår i: Annalen der Physik. - : John Wiley & Sons. - 0003-3804 .- 1521-3889. ; 532:2
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Pertsova, Anna, et al.
(författare)
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Dirac node engineering and flat bands in doped Dirac materials
- 2021
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Ingår i: Physical Review Research. - 2643-1564. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- We suggest the tried approach of impurity band engineering to produce flat bands and additional nodes in Dirac materials. We show that surface impurities give rise to nearly flat impurity bands close to the Dirac point. The hybridization of the Dirac nodal state induces the splitting of the surface Dirac nodes and the appearance of new nodes at high-symmetry points of the Brillouin zone. The results are robust and not model dependent: our tight-binding calculations are supported by a low-energy effective model of a topological insulator surface state hybridized with an impurity band. Finally, we address the effects of electron-electron interactions between localized electrons on the impurity site. We confirm that the correlation effects, while producing band hybridization and the Kondo effect, keep the hybridized band flat. Our findings open up prospects for impurity band engineering of nodal structures and flat-band correlated phases in doped Dirac materials.
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| 3. |
- Pertsova, Anna, et al.
(författare)
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Dynamically Induced Excitonic Instability in Pumped Dirac Materials
- 2020
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 532:2
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Forskningsöversikt (refereegranskat)abstract
- Driven and non-equilibrium quantum states of matter have attracted growing interest in both theoretical and experimental studies in condensed matter physics. Recent progress in realizing transient collective states in driven or pumped Dirac materials (DMs) is reviewed herein. In particular, the focus is on optically pumped DMs which are a promising platform for transient excitonic instabilities. Optical pumping combined with the linear (Dirac) dispersion of the electronic spectrum offers a knob for tuning the effective interaction between the photoexcited electrons and holes, and thus provides a way of reducing the critical coupling for excitonic instability. As a result, a transient excitonic condensate could be achieved in a pumped DM while it is not feasible in equilibrium. A unifying theoretical framework is provided for describing transient collective states in 2D and 3D DMs. The experimental signatures are described and numerical estimates of the size of the dynamically induced excitonic gaps and the values of the critical temperatures for several specific systems, are summarized. In addition, general guidelines for identifying promising material candidates are discussed. Finally, comments are provided regarding recent experimental efforts in realizing transient excitonic condensate in pumped DMs, and outstanding issues and possible future directions are outlined.
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| 4. |
- Popescu, Adrian, et al.
(författare)
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Optical Response of MoTe2 and WTe2 Weyl Semimetals : Distinguishing between Bulk and Surface Contributions
- 2020
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Ingår i: Advanced Theory and Simulations. - : Wiley. - 2513-0390. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- A first-principles investigation of the optical response of the Weyl Semimetals MoTe2 and WTe2 is presented. The approach, based on combining two formulations, allows to both separate the intraband and interband parts of the optical conductivity and to distinguish between the bulk and surface contributions to the optical response. It is found that the response is truly anisotropic, with peaks that can be associated with interband transitions involving either bulk or surface states. The role of the relaxation time, and the relation of the calculated results with available experimental measurements, are also discussed. Furthermore, the approach reported is transferable to any system, topologically trivial or non-trivial, thus addressing the long-standing need for comprehensive characterization of the optical response.
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| 5. |
- Pournaghavi, Nezhat, et al.
(författare)
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Nonlocal sidewall response and deviation from exact quantization of the topological magnetoelectric effect in axion-insulator thin films
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:20
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Tidskriftsartikel (refereegranskat)abstract
- Topological insulator (TI) thin films with surface magnetism are expected to exhibit a quantized anomalous Hall effect (QAHE) when the magnetizations on the top and bottom surfaces are parallel, and a quantized topological magnetoelectric effect (QTME) when the magnetizations have opposing orientations (axion-insulator phase) and the films are sufficiently thick. We present a unified picture of both effects that associates deviations from exact quantization of the QTME caused by finite thickness with nonlocality in the sidewall current response function. Using realistic tight-binding model calculations, we show that in Bi2Se3 TI thin films, deviations from quantization in the axion-insulator phase are reduced in size when the exchange coupling of tight-binding model basis states to the local magnetization near the surface is strengthened. Stronger exchange coupling also reduces the effect of potential disorder, which is unimportant for the QAHE but detrimental for the QTME, which requires that the Fermi energy lie inside the gap at all positions.
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| 6. |
- Yilmaz, T., et al.
(författare)
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Gap-like feature observed in the non-magnetic topological insulators
- 2020
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 32:14
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Tidskriftsartikel (refereegranskat)abstract
- Non-magnetic gap at the Dirac point of topological insulators remains an open question in the field. Here, we present angle-resolved photoemission spectroscopy experiments performed on Cr-doped Bi2Se3 and showed that the Dirac point is progressively buried by the bulk bands and a low spectral weight region in the vicinity of the Dirac point appears. These two mechanisms lead to spectral weight suppression region being mistakenly identified as an energy gap in earlier studies. We further calculated the band structure and found that the original Dirac point splits into two nodes due to the impurity resonant states and the energy separation between the nodes is the low density of state region which appears to be like an energy gap in potoemission experiments. We supported our arguments by presenting photoemission experiments carried out with on- and off- resonant photon energies. Our observation resolves the widely debated questions of apparent energy gap opening at the Dirac point without long range ferromagnetic order in topological insulators.
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