scholarly journals Structural fluctuations cause spin-split states in tetragonal (CH3NH3)PbI3 as evidenced by the circular photogalvanic effect

2018 ◽  
Vol 115 (38) ◽  
pp. 9509-9514 ◽  
Author(s):  
Daniel Niesner ◽  
Martin Hauck ◽  
Shreetu Shrestha ◽  
Ievgen Levchuk ◽  
Gebhard J. Matt ◽  
...  
Keyword(s):  
Band Gap ◽  
Tetragonal Phase ◽  
High Efficiency ◽  
Polarized Light ◽  
Spin Splitting ◽  
Rashba Effect ◽  
Photogalvanic Effect ◽  
Circularly Polarized Light ◽  
Structural Fluctuations ◽  
Indirect Band Gap

Lead halide perovskites are used in thin-film solar cells, which owe their high efficiency to the long lifetimes of photocarriers. Various calculations find that a dynamical Rashba effect could significantly contribute to these long lifetimes. This effect is predicted to cause a spin splitting of the electronic bands of inversion-symmetric crystalline materials at finite temperatures, resulting in a slightly indirect band gap. Direct experimental evidence of the existence or the strength of the spin splitting is lacking. Here, we resonantly excite photocurrents in single crystalline (CH3NH3)PbI3 with circularly polarized light to clarify the existence of spin splittings in the band structure. We observe a circular photogalvanic effect, i.e., the photocurrent depends on the light helicity, in both orthorhombic and tetragonal (CH3NH3)PbI3. At room temperature, the effect peaks for excitation photon energies ΔE=110 meV below the direct optical band gap. Temperature-dependent measurements reveal a sign change of the effect at the orthorhombic–tetragonal phase transition, indicating different microscopic origins in the two phases. Within the tetragonal phase, both ΔE and the amplitude of the circular photogalvanic effect increase with temperature. Our findings support a dynamical Rashba effect in this phase, i.e., a spin splitting caused by thermally induced structural fluctuations which break inversion symmetry.

High-efficiency generation of circularly polarized light via symmetry-induced anomalous reflection

2015 ◽  
Vol 91 (12) ◽  
Author(s):  
Shang-Chi Jiang ◽  
Xiang Xiong ◽  
Yuan-Sheng Hu ◽  
Sheng-Wei Jiang ◽  
Yu-Hui Hu ◽  
...  
Keyword(s):  
High Efficiency ◽  
Polarized Light ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Anomalous Reflection

Optical Direct and Indirect Excitation of Er3+ Ions In Silicon

1993 ◽  
Vol 301 ◽  
Author(s):  
A. Majima ◽  
S. Uekusa ◽  
K. Ootake ◽  
K. Abe ◽  
M. Kumagai
Keyword(s):  
Energy Level ◽  
Ion Implantation ◽  
Band Gap ◽  
Thermal Diffusion ◽  
High Efficiency ◽  
Optical Excitation ◽  
Silicon Substrates ◽  
Photoluminescence Excitation ◽  
Direct Excitation ◽  
Indirect Band Gap

ABSTRACTOptical direct and indirect excitation of erbium (Er) ions in silicon substrates was performed in order to investigate the high efficiency of Er3+− related 1.54µm emission (4I13/2→4I15/2) for direct excitation that is not concerned with the indirect band gap and low quantum efficiency of a Si host. The samples were prepared by ion-implantation or thermal diffusion methods. In each sample, photoluminescence (PL) showed the peaks originating from 4I13/2→4I15/2 of Er3+ ions.In Er thermally diffused samples, optical excitation for energy level 4I11/2 of Er3+ ions was successfully effected by photoluminescence excitation spectroscopy (PLE). The PLE spectra consisted six peaks (963. lnm, 965.Onm, 976.lnm, 978.9nm and 980.9nm) which were caused by direct excitation (4I15/2→4I11/2) of Er3+ ions. The emission directly excited is about 2 times more intense than the indirectly excited emission. The six peaks originating from the splitting of the 4I11/2 levels meant that Er3+ ions were in the sites of noncubic symmetry. The samples prepared by Er ion-implantation did not show the effect.

Spin-dependent electron transport in ferromagnet/semiconductor Schottky barrier structures

2000 ◽  
Vol 614 ◽  
Author(s):  
Atsufumi Hirohata ◽  
Yong-Bing Xu ◽  
Christian M. Guertler ◽  
J. Anthony ◽  
C. Bland ◽  
...  
Keyword(s):  
Electron Transport ◽  
Schottky Barrier ◽  
Schottky Barrier Height ◽  
High Efficiency ◽  
Electron Tunneling ◽  
Spin Injection ◽  
Polarized Light ◽  
Film Plane ◽  
Circularly Polarized Light ◽  
Spin Polarized

ABSTRACTClear evidence for high efficiency spin-polarized electron transport across ferromagnet/semiconductor Schottky barrier interfaces was observed in Ni80Fe20/GaAs structures. Circularly polarized light was used to excite electrons with a spin polarization perpendicular to the film plane. At negative bias, an almost constant difference between the helicity-dependent photocurrent obtained for the magnetization parallel and perpendicular to the photon helicity was detected. An effective asymmetry, A, was also estimated from the helicity-dependent photocurrent difference, attributed to spin-polarized electron tunneling from GaAs to NiFe (spin filtering). A decreases with increasing photon energy, which is consistent with the energy-dependence of the asymmetry of photoexcited electrons in GaAs. Weak spin injection from NiFe to GaAs was seen at a bias corresponding to the Schottky barrier height, which is likely to occur via a ballistic process.

Optical Direct and Indirect Excitation of Er3+ Ions in Silicon

1993 ◽  
Vol 298 ◽  
Author(s):  
A. Majima ◽  
S. Uekusa ◽  
K. Ootake ◽  
K. Abe ◽  
M. Kumagai
Keyword(s):  
Energy Level ◽  
Ion Implantation ◽  
Band Gap ◽  
Thermal Diffusion ◽  
High Efficiency ◽  
Optical Excitation ◽  
Silicon Substrates ◽  
Photoluminescence Excitation ◽  
Direct Excitation ◽  
Indirect Band Gap

AbstractOptical direct and indirect excitation of erbium (Er) ions in silicon substrates was performed in order to investigate the high efficiency of Er3+− related 1.54μm emission (4I13/2→4I15/2) for direct excitation that is not concerned with the indirect band gap and low quantum efficiency of a Si host. The samples were prepared by ion-implantation or thermal diffusion methods. In each sample, photoluminescence (PL) showed the peaks originating from 4I13/2→4I15/2 of Er3+ ions.In Er thermally diffused samples, optical excitation for energy level 4I11/2 of Er3+ ions was successfully effected by photoluminescence excitation spectroscopy (PLE). The PLE spectra consisted six peaks (963.1nm, 965.0nm, 976.lnm, 978.9nm and 980.9nm) which were caused by direct excitation (4I15/2→4I11/2) of Er3+ ions. The emission directly excited is about 2 times more intense than the indirectly excited emission. The six peaks originating from the splitting of the 4I11/2 levels meant that Er3+ ions were in the sites of noncubic symmetry. The samples prepared by Er ion-implantation did not show the effect.

scholarly journals Dynamically reconfigurable high-efficiency terahertz metasurface holograms

2021 ◽  
Vol 8 ◽  
pp. 2
Author(s):  
Mengyuan Hu ◽  
Zhen Tian
Keyword(s):  
Gallium Arsenide ◽  
High Efficiency ◽  
Polarized Light ◽  
Pump Light ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Time Dynamic ◽  
Dynamically Reconfigurable ◽  
Dynamic Display ◽  
Simulation Results

A reflective, dynamically reconfigurable, high-efficiency metasurface holographic scheme is presented in this paper, which is realized by pumping thin gallium arsenide wafers with a structured femtosecond laser. When the terahertz (THz) passes through the gallium arsenide wafer (GaAs), the pattern carried by the pump light is converted into the complex permittivity of the light carrier density distribution on the gallium arsenide wafer, which modulates the wafer, thereby changing the transmittance of the THz wave. The wavefront of the THz beam is determined by changing the shape and direction of the projected resonator on the DMD by Pancharatnam-Berry (P-B) phase principle. The numerical simulation results show that different holograms can be obtained by dynamically switching the projection on the DMD, and the orthogonal conversion efficiency of circularly polarized light can reach 90%. The holographic scheme proposed in this paper is convenient and fast and may advance the real-time dynamic conversion and dynamic display of holograms.

Optically Induced and Detected Spin Current

2017 ◽  
Author(s):  
A. Hirohata ◽  
J.-Y. Kim
Keyword(s):  
Band Gap ◽  
Polarized Light ◽  
Spin Current ◽  
Polarized Electrons ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Spin Polarized ◽  
Electron Hole Pair ◽  
Tunnelling Microscopy ◽  
Optically Induced

This chapter presents an alternative method of injecting spin-polarized electrons into a nonmagnetic semiconductor through photoexcitation. This method uses circularly-polarized light, whose energy needs to be the same as, or slightly larger than, the semiconductor band-gap, to excite spin-polarized electrons. This process will introduce a spin-polarized electron-hole pair, which can be detected as electrical signals. Such an optically induced spin-polarized current can only be generated in a direct band-gap semiconductor due to the selection rule described in the following sections. This introduction of circularly polarized light can also be used for spin-polarized scanning tunnelling microscopy.

scholarly journals Anisotropic circular photogalvanic effect in colloidal tin sulfide nanosheets

Nanoscale ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 6256-6262
Author(s):  
Mohammad Mehdi Ramin Moayed ◽  
Fu Li ◽  
Philip Beck ◽  
Jan-Christian Schober ◽  
Christian Klinke
Keyword(s):  
Polarized Light ◽  
Tin Sulfide ◽  
Photogalvanic Effect ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Electronic Response

The electronic response of colloidal 2D tin sulfide crystals to the illumination with circularly polarized light has been investigated. The nanocrystals show a strong anisotropic circular photogalvanic effect.

Janus MSiGeN4 (M = Zr and Hf) monolayers derived from centrosymmetric β-MA2Z4: A first-principles study

2021 ◽  
Vol 42 (12) ◽  
pp. 122002
Author(s):  
Xiaoshu Guo ◽  
Sandong Guo
Keyword(s):  
Band Gap ◽  
Tensile Strain ◽  
Compressive Strain ◽  
Valence Band Maximum ◽  
Spin Splitting ◽  
Piezoelectric Response ◽  
Generalized Gradient ◽  
Thermal Stabilities ◽  
Out Of Plane ◽  
Indirect Band Gap

Abstract A two-dimensional (2D) MA2Z4 family with and phases has been attracting tremendous interest, the MoSi2N4 and WSi2N4 of which have been successfully fabricated ( Science 369, 670 (2020)). Janus monolayers have been achieved in many 2D families, so it is interesting to construct a Janus monolayer from the MA2Z4 family. In this work, Janus MSiGeN4 (M = Zr and Hf) monolayers are predicted from -MA2Z4, which exhibit dynamic, mechanical and thermal stabilities. It is found that they are indirect band-gap semiconductors by using generalized gradient approximation (GGA) plus spin-orbit coupling (SOC). With biaxial strain from 0.90 to 1.10, the energy band gap shows a nonmonotonic behavior due to a change of conduction band minimum (CBM). A semiconductor to metal transition can be induced by both compressive and tensile strains, and the phase transformation point is about 0.96 for compressive strain and 1.10 for tensile strain. The tensile strain can change the positions of CBM and valence band maximum (VBM), and can also induce the weak Rashba-type spin splitting near CBM. For MSiGeN4 (M = Zr and Hf) monolayers, both an in-plane and out-of-plane piezoelectric response can be produced, when a uniaxial strain in the basal plane is applied, which reveals the potential as piezoelectric 2D materials. The high absorption coefficients in the visible light region suggest that MSiGeN4 (M = Zr and Hf) monolayers have potential photocatalytic applications. Our works provide an idea to achieve a Janus structure from the MA2Z4 family, and can hopefully inspire further research exploring Janus MA2Z4 monolayers.

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