scholarly journals Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials

2020 ◽  
Vol 6 (9) ◽  
pp. eaay2730 ◽  
Author(s):  
Michael Schüler ◽  
Umberto De Giovannini ◽  
Hannes Hübener ◽  
Angel Rubio ◽  
Michael A. Sentef ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Great Promise ◽  
Two Dimensional ◽  
Topological Properties ◽  
Time Resolved ◽  
Berry Curvature ◽  
Two Dimensional Materials ◽  
Geometrical Character ◽  
Chern Insulators ◽  
Topological Character

Topologically nontrivial two-dimensional materials hold great promise for next-generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular dichroism angle-resolved photoelectron spectroscopy provides a powerful tool that can resolve the topological and quantum-geometrical character in momentum space. In particular, we investigate how to map out the signatures of the momentum-resolved Berry curvature in two-dimensional materials by exploiting its intimate connection to the orbital polarization. A spin-resolved detection of the photoelectrons allows one to extend the approach to spin-Chern insulators. The present proposal can be extended to address topological properties in materials out of equilibrium in a time-resolved fashion.

Flexible Piezoelectricity of Two-Dimensional Materials Governed by Effective Berry Curvature

2021 ◽  
pp. 8220-8228
Author(s):  
Yilimiranmu Rouzhahong ◽  
Chao Liang ◽  
Chong Li ◽  
Huashan Li ◽  
Biao Wang
Keyword(s):  
Two Dimensional ◽  
Berry Curvature ◽  
Two Dimensional Materials

scholarly journals Tunable optical absorption in silicene molecules

2016 ◽  
Vol 4 (31) ◽  
pp. 7387-7390 ◽  
Author(s):  
Junais Habeeb Mokkath ◽  
Udo Schwingenschlögl
Keyword(s):  
Optical Absorption ◽  
Band Gap ◽  
Solar Spectrum ◽  
Great Promise ◽  
Two Dimensional ◽  
Wide Range ◽  
Two Dimensional Materials ◽  
Tunable Band Gap

Two-dimensional materials with a tunable band gap that covers a wide range of the solar spectrum hold great promise for sunlight harvesting.

scholarly journals A Review on Applications of Two-Dimensional Materials in Surface-Enhanced Raman Spectroscopy

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Ming Xia
Keyword(s):  
Raman Spectroscopy ◽  
2D Materials ◽  
Surface Enhanced Raman Spectroscopy ◽  
Great Promise ◽  
Two Dimensional ◽  
Raman Enhancement ◽  
Two Dimensional Materials ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Recent Developments

Two-dimensional (2D) materials, such as graphene and MoS2, have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials’ application in surface-enhanced Raman spectroscopy. This review paper focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.

scholarly journals Phonon-assisted processes in the ultraviolet-transient optical response of graphene

2019 ◽  
Vol 3 (1) ◽  
Author(s):  
Dino Novko ◽  
Marko Kralj
Keyword(s):  
Dominant Role ◽  
Chemical Doping ◽  
Two Dimensional ◽  
Many Body ◽  
Time Resolved ◽  
Electron Phonon Interaction ◽  
Spectral Changes ◽  
Two Dimensional Materials ◽  
Many Body Interactions

AbstractMany recent experiments investigated potential and attractive means of modifying many-body interactions in two-dimensional materials through time-resolved spectroscopy techniques. However, the role of ultrafast phonon-assisted processes in two-dimensional systems is rarely discussed in depth. Here, we investigate the role of electron–phonon interaction in the transient optical absorption of graphene by means of first-principles methods. It is shown at equilibrium that the phonon-assisted transitions renormalize significantly the electronic structure. As a result, absorption peak around the Van-Hove singularity broadens and redshifts by ~100 meV. In addition, temperature increase and chemical doping are shown to notably enhance these phonon-assisted features. In the photoinduced transient response, we obtain spectral changes in close agreement with the experiments, and we associate them to the strong renormalization of occupied and unoccupied $$\pi$$π bands, which predominantly comes from the coupling with the zone-center $${E}_{2g}$$E2g optical phonon. Our estimation of the Coulomb interaction effects shows that the phonon-assisted processes can have a dominant role even in the subpicosecond regime.

scholarly journals Unraveling materials Berry curvature and Chern numbers from real-time evolution of Bloch states

2019 ◽  
Vol 116 (10) ◽  
pp. 4135-4140 ◽  
Author(s):  
Dongbin Shin ◽  
Shunsuke A. Sato ◽  
Hannes Hübener ◽  
Umberto De Giovannini ◽  
Jeongwoo Kim ◽  
...  
Keyword(s):  
Real Time ◽  
Linear Response ◽  
Quantum Spin ◽  
Topological Properties ◽  
Berry Curvature ◽  
Topological Materials ◽  
Chern Numbers ◽  
Nonequilibrium States ◽  
Topological Characteristics ◽  
Topological Character

Materials can be classified by the topological character of their electronic structure and, in this perspective, global attributes immune to local deformations have been discussed in terms of Berry curvature and Chern numbers. Except for instructional simple models, linear response theories have been ubiquitously used in calculations of topological properties of real materials. Here we propose a completely different and versatile approach to obtain the topological characteristics of materials by calculating physical observables from the real-time evolving Bloch states: The cell-averaged current density reveals the anomalous velocities that lead to the conductivity quantum. Results for prototypical cases are shown, including a spin-frozen valley Hall and a quantum anomalous Hall insulator. The advantage of this method is best illustrated by the example of a quantum spin Hall insulator: The quantized spin Hall conductivity is straightforwardly obtained irrespective of the non-Abelian nature in its Berry curvature. Moreover, the method can be extended to the description of real observables in nonequilibrium states of topological materials.

scholarly journals Topological Edge States of a Majorana BBH Model

2021 ◽  
Vol 6 (2) ◽  
pp. 15
Author(s):  
Alfonso Maiellaro ◽  
Roberta Citro
Keyword(s):  
2D Materials ◽  
Finite Size ◽  
Majorana Fermions ◽  
Topological Phase ◽  
Two Dimensional ◽  
Edge States ◽  
Finite Size Scaling ◽  
Topological Properties ◽  
Berry Curvature ◽  
Topological Superconductors

We investigate a Majorana Benalcazar–Bernevig–Hughes (BBH) model showing the emergence of topological corner states. The model, consisting of a two-dimensional Su–Schrieffer–Heeger (SSH) system of Majorana fermions with π flux, exhibits a non-trivial topological phase in the absence of Berry curvature, while the Berry connection leads to a non-trivial topology. Indeed, the system belongs to the class of second-order topological superconductors (HOTSC2), exhibiting corner Majorana states protected by C4 symmetry and reflection symmetries. By calculating the 2D Zak phase, we derive the topological phase diagram of the system and demonstrate the bulk-edge correspondence. Finally, we analyze the finite size scaling behavior of the topological properties. Our results can serve to design new 2D materials with non-zero Zak phase and robust edge states.

scholarly journals Influence of anisotropy, tilt and pairing of Weyl nodes: the Weyl semimetals TaAs, TaP, NbAs and NbP

2020 ◽  
Vol 93 (8) ◽  
Author(s):  
Davide Grassano ◽  
Olivia Pulci ◽  
Elena Cannuccia ◽  
Friedhelm Bechstedt
Keyword(s):  
Topological Properties ◽  
Strong Anisotropy ◽  
Berry Curvature ◽  
Electronic Spin ◽  
Weyl Semimetals ◽  
Connection Line ◽  
Spin Texture ◽  
Weyl Fermion ◽  
Topological Character ◽  
Conventional Picture

Abstract By means of ab initio band structure methods and model Hamiltonians we investigate the electronic, spin and topological properties of four monopnictides crystallizing in bct structure. We show that the Weyl bands around a WP W1 or W2 possess a strong anisotropy and tilt of the accompanying Dirac cones. These effects are larger for W2 nodes than for W1 ones. The node tilts and positions in energy space significantly influence the DOS of single-particle Weyl excitations. The node anisotropies destroy the conventional picture of (anti)parallel spin and wave vector of a Weyl fermion. This also holds for the Berry curvature around a node, while the monopole charges are independent as integrated quantities. The pairing of the nodes strongly modifies the spin texture and the Berry curvature for wave vectors in between the two nodes. Spin components may change their orientation. Integrals over planes perpendicular to the connection line yield finite Zak phases and winding numbers for planes between the two nodes, thereby indicating the topological character. Graphical abstract

Two dimensional Sr silicate grown on Si(001) studied using X-ray Photoelectron Spectroscopy

2006 ◽  
Vol 132 ◽  
pp. 87-90
Author(s):  
M. El Kazzi ◽  
G. Delhaye ◽  
S. Gaillard ◽  
E. Bergignat ◽  
G. Hollinger
Keyword(s):  
Photoelectron Spectroscopy ◽  
Two Dimensional ◽  
X Ray
Sign in / Sign up

Export Citation Format

Share Document