scholarly journals Direct time-domain observation of attosecond final-state lifetimes in photoemission from solids

Science ◽  
2016 ◽  
Vol 353 (6294) ◽  
pp. 62-67 ◽  
Author(s):  
Zhensheng Tao ◽  
Cong Chen ◽  
Tibor Szilvási ◽  
Mark Keller ◽  
Manos Mavrikakis ◽  
...  
Keyword(s):  
Band Structure ◽  
Strong Dependence ◽  
Emission Angle ◽  
Spectroscopic Techniques ◽  
Final State ◽  
Band Dispersion ◽  
Electron Escape ◽  
State Band ◽  
The Difference ◽  
Valence Bands

Attosecond spectroscopic techniques have made it possible to measure differences in transport times for photoelectrons from localized core levels and delocalized valence bands in solids. We report the application of attosecond pulse trains to directly and unambiguously measure the difference in lifetimes between photoelectrons born into free electron–like states and those excited into unoccupied excited states in the band structure of nickel (111). An enormous increase in lifetime of 212 ± 30 attoseconds occurs when the final state coincides with a short-lived excited state. Moreover, a strong dependence of this lifetime on emission angle is directly related to the final-state band dispersion as a function of electron transverse momentum. This finding underscores the importance of the material band structure in determining photoelectron lifetimes and corresponding electron escape depths.

scholarly journals The Highly Uniform Photoresponsivity from Visible to Near IR Light in Sb2Te3 Flakes

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1535
Author(s):  
Shiu-Ming Huang ◽  
Jai-Lung Hung ◽  
Mitch Chou ◽  
Chi-Yang Chen ◽  
Fang-Chen Liu ◽  
...  
Keyword(s):  
Band Structure ◽  
Energy Difference ◽  
Experimental Result ◽  
Light Illumination ◽  
Near Ir ◽  
State Band ◽  
Valence Bands ◽  
Low Dimensional ◽  
Low Dimensional Materials ◽  
Ir Light

Broadband photosensors have been widely studied in various kinds of materials. Experimental results have revealed strong wavelength-dependent photoresponses in all previous reports. This limits the potential application of broadband photosensors. Therefore, finding a wavelength-insensitive photosensor is imperative in this application. Photocurrent measurements were performed in Sb2Te3 flakes at various wavelengths ranging from visible to near IR light. The measured photocurrent change was insensitive to wavelengths from 300 to 1000 nm. The observed wavelength response deviation was lower than that in all previous reports. Our results show that the corresponding energies of these photocurrent peaks are consistent with the energy difference of the density of state peaks between conduction and valence bands. This suggests that the observed photocurrent originates from these band structure peak transitions under light illumination. Contrary to the most common explanation that observed broadband photocurrent carrier is mainly from the surface state in low-dimensional materials, our experimental result suggests that bulk state band structure is the main source of the observed photocurrent and dominates the broadband photocurrent.

scholarly journals Photoemission Spectroscopy of Single Crystal HTSC Materials: A Fermi Liquid Electronic Structure

1989 ◽  
Vol 156 ◽  
Author(s):  
A. J. Arko ◽  
R. S. List ◽  
R. J. Bartlett ◽  
S. W. Cheong ◽  
C. G. Olson ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Single Crystal ◽  
Fermi Liquid ◽  
Wide Band ◽  
Photoemission Spectroscopy ◽  
Correlation Effects ◽  
Band Dispersion ◽  
Valence Bands ◽  
Orbital Character

ABSTRACTPhotoemission spectra from HTSC materials ( primarily 123 -type ), cleaved and measured at 20K, reveal a rich DOS structure which compares favorably with a calculated band structure, except for a residual 0.5 eV shift which may reflect some correlation effects. Band dispersion is observed throughout the valence bands, with clear evidence for a 0.2 eV wide band dispersing through EF. The orbital character at EF is a mix of Cu-3d and O-2p. There is unambiguous evidence for a large BCS-like gap (2Δ≥ 4kTc).

Band structure investigation of chalcopyrite CuInSe2(001) by angle-resolved photoelectron spectroscopy

2005 ◽  
Vol 865 ◽  
Author(s):  
Ralf Hunger ◽  
Christian Pettenkofer
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Valence Band ◽  
Photoelectron Spectroscopy ◽  
Bulk Composition ◽  
Synchrotron Source ◽  
Band Dispersion ◽  
Low Energy Electron ◽  
Copper Chalcopyrite ◽  
Valence Bands

AbstractClean and ordered chalcopyrite CuInSe2 surfaces are a precondition for the study of the electronic structure by angle-resolved photoelectron spectroscopy. The preparation of welldefined CuInSe2(001) surfaces by the combination of molecular beam epitaxy and a selenium capping and decapping process is described. The surface structure of CuInSe2 epilayers with different bulk composition is compared and analysed by low-energy electron diffraction.Employing near-stoichiometric surfaces, the valence electronic structure of CuInSe2 was investigated by angle-resolved photoelectron spectroscopy at the synchrotron source BESSY 2. This is the first study of the valence band structure of a copper chalcopyrite semiconductor material by photoelectron spectroscopy. The valence band dispersion along τT, i.e. the [001] direction, was investigated by a variation of the excitation energy from 10 to 35 eV under normal emission, and the band dispersion along τT, i.e. the [110] direction, was analysed by angular scans with hv = 13 eV.The valence bands derived from antibonding and bonding Se4p-Cu3d hybrid orbitals, nonbonding Cu3d states and In-Se hybrid states are clearly indentified. The strongest dispersion is found for the topmost valence band with a bandwidth of ∼0.7 eV from τ to T. From τ to N, the observed dispersion was 0.5 eV. The experimental valence bands are discussed in relation to calculated band structures in the literature.

RKKY interaction in topological crystalline insulators

2020 ◽  
Author(s):  
Seyyed Hosein Ganjipour
Keyword(s):  
Band Structure ◽  
Exchange Coupling ◽  
Magnetic Impurities ◽  
Rkky Interaction ◽  
Magnetic Ground State ◽  
Magnetic Exchange ◽  
Magnetic Exchange Coupling ◽  
Spatial Configurations ◽  
State Band ◽  
Topological Crystalline Insulators

We theoretically study the Ruderman-Kittle-Kasuya-Yosida (RKKY) interaction between two magnetic impurities embedded on the (001) surface of a topological crystalline insulator (TCI), using the Green’s function method. Highly anisotropic band structure of TCI, gives rise to a highly anisotropic magnetic exchange coupling. We show that the interaction is oscillatory; the amplitude and wavelength of oscillations have angular dependence arising from the anisotropy of the surface state band structure. The spatial configurations of the magnetic impurities can also dramatically change the quality and quantity of the RKKY interaction. We find a strong anisotropy of the exchange interaction and the magnetic ground state of two magnetic adatoms can be tuned by changing the rotational configuration of impurities. It is found that the three types of interactions contribute to the magnetic exchange coupling in the (001) TCI surfaces: the Heisenberg, Dzyaloshinsky-Moriya, and Ising types. Our results will open up a new route toward spintronics based on TCIs.

Dynamics of a Resistive Sheet Pinch

1982 ◽  
Vol 37 (8) ◽  
pp. 840-847 ◽  
Author(s):  
D. Biskamp
Keyword(s):  
Mhd Equations ◽  
Magnetic Islands ◽  
Final State ◽  
Flux Function ◽  
Tearing Modes ◽  
Parallel Diffusion ◽  
Strong Shear ◽  
Resistive Sheet ◽  
Special Distribution ◽  
The Difference

The dynamic evolution and the saturated state of a long sheet pinch subject to growth of resistive tearing modes was investigated by numerical solution of the 2D MHD equations. Both the compressible and the incompressible equations were used, and the difference is found to be negligible. The necessity of considering a resistive equilibrium is stressed. The paper concentrates on a static equilibrium maintained by an external electric field and requiring a special distribution of the resistivity η. In addition the dynamics of the resistivity plays an important part. Assuming η to be time independent, the sheet pinch develops a number of soliton-like magnetic islands, which coalesce. The final state consists of a single soliton, while the generation of further sol-itons is inhibited by a strong shear flow allong the current sheet. When allowance is made for parallel diffusion of the resistivity such that η is essentially a flux function, the final state is quite different. Here the longest wavelength dominates, leading to a single, large island and completely destroying the original sheet pinch

scholarly journals Comprehensive Study of Cross-Section Dependent Effective Masses for Silicon Based Gate-All-Around Transistors

2019 ◽  
Vol 9 (9) ◽  
pp. 1895 ◽  
Author(s):  
Oves Badami ◽  
Cristina Medina-Bailon ◽  
Salim Berrada ◽  
Hamilton Carrillo-Nunez ◽  
Jaeyhun Lee ◽  
...  
Keyword(s):  
Band Structure ◽  
Cross Section ◽  
Electronic Band Structure ◽  
Strong Dependence ◽  
Simulation Software ◽  
Cross Sectional ◽  
Electronic Band ◽  
Effective Masses ◽  
Simulation Engine ◽  
Silicon Based

The use of bulk effective masses in simulations of the modern-day ultra-scaled transistor is erroneous due to the strong dependence of the band structure on the cross-section dimensions and shape. This has to be accounted for in transport simulations due to the significant impact of the effective masses on quantum confinement effects and mobility. In this article, we present a methodology for the extraction of the electron effective masses, in both confinement and the transport directions, from the simulated electronic band structure of the nanowire channel. This methodology has been implemented in our in-house three-dimensional (3D) simulation engine, NESS (Nano-Electronic Simulation Software). We provide comprehensive data for the effective masses of the silicon-based nanowire transistors (NWTs) with technologically relevant cross-sectional area and transport orientations. We demonstrate the importance of the correct effective masses by showing its impact on mobility and transfer characteristics.

scholarly journals Limitation of symmetry breaking by gravitational collapse: the revisit of Lin–Mestel–Shu instability

2020 ◽  
Vol 498 (1) ◽  
pp. 310-319
Author(s):  
Tirawut Worrakitpoonpon
Keyword(s):  
Gravitational Collapse ◽  
Power Law ◽  
Particle Number ◽  
Density Fluctuations ◽  
Shape Evolution ◽  
Critical Number ◽  
Initial State ◽  
Final State ◽  
Numerical Work ◽  
The Difference

ABSTRACT We revisit the topic of shape evolution during the spherical collapse of an N-body system. Our main objective is to investigate the critical particle number below which, during a gravitational collapse, the amplification of triaxiality from initial fluctuations is effective, and above which it is ineffective. To this aim, we develop the Lin–Mestel–Shu theory for a system of particles initially with isotropic velocity dispersion and with a simple power-law density profile. We first determine, for an unstable cloud, two radii corresponding to the balance of two opposing forces and their fluctuations: such radii fix the sizes of the non-collapsing region and the triaxial seed from density fluctuations. We hypothesize that the triaxial degree of the final state depends on which radius is dominant prior to the collapse phase leading to a different scheme of the self-consistent shape evolution of the core and the rest of the system. The condition where the two radii are equal therefore identifies the critical particle number, which can be expressed as the function of the parameters of initial state. In numerical work, we can pinpoint such a critical number by comparing the virialized flattening with the initial flattening. The difference between these two quantities agrees with the theoretical predictions only for the power-law density profiles with an exponent in the range [0, 0.25]. For higher exponents, results suggest that the critical number is above the range of simulated N. We speculate that there is an additional mechanism, related to strong density gradients that increases further the flattening, requiring higher N to further weaken the initial fluctuations.

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