scholarly journals Low-energy model and electron-hole doping asymmetry of single-layer Ruddlesden-Popper iridates

2015 ◽  
Vol 92 (8) ◽  
Author(s):  
Alexander Hampel ◽  
Christoph Piefke ◽  
Frank Lechermann
Keyword(s):  
Single Layer ◽  
Energy Model ◽  
Low Energy ◽  
Hole Doping ◽  
Electron Hole

scholarly journals The ultrafast onset of exciton formation in 2D semiconductors

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Chiara Trovatello ◽  
Florian Katsch ◽  
Nicholas J. Borys ◽  
Malte Selig ◽  
Kaiyuan Yao ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Transition Metal Dichalcogenides ◽  
Single Layer ◽  
Underlying Mechanism ◽  
Relaxation Dynamics ◽  
Electron Hole ◽  
Layer Transition ◽  
Coulombic Interactions ◽  
Formation Dynamics ◽  
Metal Dichalcogenides

Abstract The equilibrium and non-equilibrium optical properties of single-layer transition metal dichalcogenides (TMDs) are determined by strongly bound excitons. Exciton relaxation dynamics in TMDs have been extensively studied by time-domain optical spectroscopies. However, the formation dynamics of excitons following non-resonant photoexcitation of free electron-hole pairs have been challenging to directly probe because of their inherently fast timescales. Here, we use extremely short optical pulses to non-resonantly excite an electron-hole plasma and show the formation of two-dimensional excitons in single-layer MoS2 on the timescale of 30 fs via the induced changes to photo-absorption. These formation dynamics are significantly faster than in conventional 2D quantum wells and are attributed to the intense Coulombic interactions present in 2D TMDs. A theoretical model of a coherent polarization that dephases and relaxes to an incoherent exciton population reproduces the experimental dynamics on the sub-100-fs timescale and sheds light into the underlying mechanism of how the lowest-energy excitons, which are the most important for optoelectronic applications, form from higher-energy excitations. Importantly, a phonon-mediated exciton cascade from higher energy states to the ground excitonic state is found to be the rate-limiting process. These results set an ultimate timescale of the exciton formation in TMDs and elucidate the exceptionally fast physical mechanism behind this process.

scholarly journals Emergence of quasiparticles in a doped Mott insulator

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Yao Wang ◽  
Yu He ◽  
Krzysztof Wohlfeld ◽  
Makoto Hashimoto ◽  
Edwin W. Huang ◽  
...  
Keyword(s):  
Hubbard Model ◽  
Single Layer ◽  
Mott Insulator ◽  
Spectral Weight ◽  
Particle Spectrum ◽  
Electron Hole ◽  
Strong Electron ◽  
Side Band ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Weakly Coupled

AbstractHow a Mott insulator develops into a weakly coupled metal upon doping is a central question to understanding various emergent correlated phenomena. To analyze this evolution and its connection to the high-Tc cuprates, we study the single-particle spectrum for the doped Hubbard model using cluster perturbation theory on superclusters. Starting from extremely low doping, we identify a heavily renormalized quasiparticle dispersion that immediately develops across the Fermi level, and a weakening polaronic side band at higher binding energy. The quasiparticle spectral weight roughly grows at twice the rate of doping in the low doping regime, but this rate is halved at optimal doping. In the heavily doped regime, we find both strong electron-hole asymmetry and a persistent presence of Mott spectral features. Finally, we discuss the applicability of the single-band Hubbard model to describe the evolution of nodal spectra measured by angle-resolved photoemission spectroscopy (ARPES) on the single-layer cuprate La2−xSrxCuO4 (0 ≤ x ≤ 0.15). This work benchmarks the predictive power of the Hubbard model for electronic properties of high-Tc cuprates.

scholarly journals Porous materials additively manufactured at low energy: Single-layer manufacturing and characterization

2020 ◽  
Vol 191 ◽  
pp. 108654 ◽  
Author(s):  
Davoud Jafari ◽  
Koen J.H. van Alphen ◽  
Bernard J. Geurts ◽  
Wessel W. Wits ◽  
Laura Cordova Gonzalez ◽  
...  
Keyword(s):  
Porous Materials ◽  
Single Layer ◽  
Low Energy ◽  
Layer Manufacturing

scholarly journals Particle–Hole Transformation in Strongly-Doped Iron-Based Superconductors

Symmetry ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 396
Author(s):  
Jose Rodriguez
Keyword(s):  
Brillouin Zone ◽  
Single Layer ◽  
Local Moment ◽  
Hole Doping ◽  
Cooper Pairs ◽  
Fermi Surfaces ◽  
Iron Based ◽  
Magnetic Resonances ◽  
Layer Iron ◽  
Electron Pocket

An exact particle–hole transformation is discovered in a local-moment model for a single layer of heavily electron-doped FeSe. The model harbors hidden magnetic order between the iron d x z and d y z orbitals at the wavenumber ( π , π ) . It potentially is tied to the magnetic resonances about the very same Néel ordering vector that have been recently discovered in intercalated FeSe. Upon electron doping, the local-moment model successfully accounts for the electron-pocket Fermi surfaces observed experimentally at the corner of the two-iron Brillouin zone in electron-doped FeSe, as well as for isotropic Cooper pairs. Application of the particle–hole transformation predicts a surface-layer iron-based superconductor at strong hole doping that exhibits high T c, and that shows hole-type Fermi-surface pockets at the center of the two-iron Brillouin zone.

Annealing Temperature and Substrate Effects on the Raman Spectra of Transferred CVD Graphene

2012 ◽  
Vol 1407 ◽  
Author(s):  
Barbara M. Nichols ◽  
Yasmine R. Doleyres ◽  
Gregory P. Meissner
Keyword(s):  
Raman Spectra ◽  
Intensity Ratio ◽  
Substrate Surface ◽  
Single Layer ◽  
Fused Silica ◽  
Single Layer Graphene ◽  
Hole Doping ◽  
Pmma Layer ◽  
Layer Graphene ◽  
Before And After

ABSTRACTThis work explores the influence of the post-transfer anneal temperature and the substrate on transferred graphene and its Raman properties. Graphene grown by low pressure chemical vapor deposition on copper foils was transferred to SiO2/Si, fused silica, and silicon substrates via a process that involves coating the graphene with PMMA as a protective handling layer during the wet chemical etching of the copper and then placing the PMMA/graphene onto the substrate. The PMMA layer was then removed by heating in a hydrogen/argon atmosphere at temperatures ranging from 350 to 550 °C or by exposing the PMMA to heated acetone vapor/liquid. Raman spectroscopy measurements, taken before and after PMMA removal, reveal differences in the prominent Raman features, the G and G’ peaks, upon annealing. These changes include (1) a shift in the average G and G’ peak positions when comparing Raman spectra before and after PMMA removal and (2) a decrease in the G’:G peak intensity ratio (IG’/IG), which is typically used as a measure of the number of graphene layers. For both the as-transferred graphene and graphene removed by the heated acetone, the IG’/IG peak ratio was approximately 2, indicating single layer graphene. However, when the graphene was annealed at temperatures above 350 °C, the IG’/IG intensity ratio varied from 0.5 to 1.5. These changes in the Raman spectra are similar to those observed in exfoliated single layer graphene supported on SiO2/Si substrates and are indicative of graphene-substrate interaction effects that lead to hole doping of the graphene [1,2]. These trends were observed for graphene transferred to all three substrates, regardless of the substrate surface roughness and/or composition.

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