scholarly journals Observing photo-induced chiral edge states of graphene nanoribbons in pump-probe spectroscopies

2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Yuan Chen ◽  
Yao Wang ◽  
Martin Claassen ◽  
Brian Moritz ◽  
Thomas P. Devereaux
Keyword(s):  
Graphene Nanoribbons ◽  
Topological States Of Matter ◽  
Polarized Light ◽  
Edge States ◽  
Time Resolved ◽  
Pump Probe ◽  
Circularly Polarized Light ◽  
Incoming Photon ◽  
Low Dimensional ◽  
Spectroscopic Signatures

Abstract Photo-induced edge states in low-dimensional materials have attracted considerable attention due to the tunability of topological properties and dispersion. Specifically, graphene nanoribbons have been predicted to host chiral edge modes upon irradiation with circularly polarized light. Here, we present numerical calculations of time-resolved angle resolved photoemission spectroscopy and trRIXS of a graphene nanoribbon. We characterize pump-probe spectroscopic signatures of photo-induced edge states, illustrate the origin of distinct spectral features that arise from Floquet topological edge modes, and investigate the roles of incoming photon energies and finite core–hole lifetime in RIXS. With momentum, energy, and time resolution, pump-probe spectroscopies can play an important role in understanding the behavior of photo-induced topological states of matter.

Laser Induced Periodic Surface Structure

1982 ◽  
Vol 13 ◽  
Author(s):  
H.M. Van Driel ◽  
Jeff F. Young ◽  
J.E. Sipe
Keyword(s):  
Surface Structure ◽  
Polarized Light ◽  
Beam Polarization ◽  
Time Resolved ◽  
Periodic Surface ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Surface Modes ◽  
Periodic Surface Structure ◽  
Damage Structure

ABSTRACTLaser induced periodic surface structure can be understood as a universal phenomenon which occurs when high intensity pulses are absorbed near the surface of solids or liquids. The phenomenon occurs on metals, semiconductors and insulators because of the interference between the incident pulse and an induced “radiation remnant”. This scattered field may be enhanced by the existence of true surface modes such as surface plasmons or phonon-polaritons but this is not essential. The universality characteristics include beam polarization, since we show that circularly polarized light can induce surface ripples, with the damage structure showing a dependence on the sense of rotation. We also present time resolved results of the formation of the ripples to illustrate the essential dynamical processes that occur.

Graphene nanoribbons in criss-crossed electric and magnetic fields

2010 ◽  
Vol 368 (1932) ◽  
pp. 5431-5443 ◽  
Author(s):  
Oleksiy Roslyak ◽  
Godfrey Gumbs ◽  
Danhong Huang
Keyword(s):  
Magnetic Fields ◽  
Energy Range ◽  
Bound States ◽  
Graphene Nanoribbons ◽  
Strong Electric Field ◽  
Polarized Light ◽  
Circularly Polarized Light ◽  
Electric And Magnetic Fields ◽  
Electron Transport Properties ◽  
Electrically Enhanced

Graphene nanoribbons (GNRs) in mutually perpendicular electric and magnetic fields are shown to exhibit dramatic changes in their band structure and electron-transport properties. A strong electric field across the ribbon induces multiple chiral Dirac points, closing the semiconducting gap in armchair GNRs. A perpendicular magnetic field induces partially formed Landau levels as well as dispersive surface-bound states. Each of the applied fields on its own preserves the even symmetry E k = E − k of the sub-band dispersion. When applied together, they reverse the dispersion parity to be odd, which gives E e, k =− E h,− k , and mix the electron and hole sub-bands within the energy range corresponding to the change in potential across the ribbon. This leads to oscillations of the ballistic conductance within this energy range. The broken time-reversal symmetry provides dichroism in the absorption of the circularly polarized light. As a consequence, one can observe electrically enhanced Faraday rotation, since the edges of the ribbon provide formation of the substantial density of states.

scholarly journals Light-induced topological magnons in two-dimensional van der Waals magnets

2020 ◽  
Vol 9 (4) ◽  
Author(s):  
Emil Vinas Boström ◽  
Martin Claassen ◽  
James McIver ◽  
Gregor Jotzu ◽  
Angel Rubio ◽  
...  
Keyword(s):  
Coupling Parameter ◽  
Polarized Light ◽  
Laser Pulses ◽  
Two Dimensional ◽  
Edge States ◽  
Pulse Envelope ◽  
Experimental Realization ◽  
Circularly Polarized Light ◽  
Quantum Magnet ◽  
Haldane Model

Driving a two-dimensional Mott insulator with circularly polarized light breaks time-reversal and inversion symmetry, which induces an optically-tunable synthetic scalar spin chirality interaction in the effective low-energy spin Hamiltonian. Here, we show that this mechanism can stabilize topological magnon excitations in honeycomb ferromagnets and in optical lattices. We find that the irradiated quantum magnet is described by a Haldane model for magnons that hosts topologically-protected edge modes. We study the evolution of the magnon spectrum in the Floquet regime and via time propagation of the magnon Hamiltonian for a slowly varying pulse envelope. Compared to similar but conceptually distinct driving schemes based on the Aharanov-Casher effect, the dimensionless light-matter coupling parameter \lambda = eEa/\hbar\omegaλ=eEa/ℏω at fixed electric field strength is enhanced by a factor \sim 10^5∼105. This increase of the coupling parameter allows to induce a topological gap of the order of \Delta \approx 2Δ≈2 meV with realistic laser pulses, bringing an experimental realization of light-induced topological magnon edge states within reach.

scholarly journals Twentieth century developments in photochemistry. Brief historical sketches

2001 ◽  
Vol 73 (3) ◽  
pp. 395-403 ◽  
Author(s):  
Heinz D. Roth
Keyword(s):  
Electron Transfer ◽  
Polarized Light ◽  
Photosynthetic Reaction Centers ◽  
Time Resolved ◽  
Circularly Polarized Light ◽  
Harvesting Systems ◽  
Detailed Kinetics ◽  
Kinetics Of ◽  
Physical Principles ◽  
Sequential Electron

In the 20th century, photochemistry blossomed from a poorly defined to a highly sophisticated science. Early breakthroughs in exploratory photochemistry and the underlying physical principles led to new diverse, yet inter-related areas of research. The alluring goal of asymmetric synthesis with circularly polarized light proved elusive. The discovery of the electron brought a gradual awakening to the idea of electron transfer. Time-resolved spectroscopy developed from ms to fs resolution. The field of photosynthesis progressed from an interest in function and structure of photosynthetic pigments to the isolation and structure elucidation of photosynthetic reaction centers (rhodobacter sphaeroides), to the detailed kinetics of sequential electron-transfer steps in natural and synthetic light-harvesting systems.

Differential polarization imaging of sickled cells

1988 ◽  
Vol 46 ◽  
pp. 62-63
Author(s):  
Marcos F. Maestre
Keyword(s):  
Optical Properties ◽  
Theoretical Approach ◽  
Polarized Light ◽  
Polarization Microscopy ◽  
Spectroscopic Techniques ◽  
Polarization Imaging ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Microscopic Scale ◽  
Chiral Structures

Recently we have developed a form of polarization microscopy that forms images using optical properties that have previously been limited to macroscopic samples. This has given us a new window into the distribution of structure on a microscopic scale. We have coined the name differential polarization microscopy to identify the images obtained that are due to certain polarization dependent effects. Differential polarization microscopy has its origins in various spectroscopic techniques that have been used to study longer range structures in solution as well as solids. The differential scattering of circularly polarized light has been shown to be dependent on the long range chiral order, both theoretically and experimentally. The same theoretical approach was used to show that images due to differential scattering of circularly polarized light will give images dependent on chiral structures. With large helices (greater than the wavelength of light) the pitch and radius of the helix could be measured directly from these images.

Pump-Probe Measurements Using Silicon Nanocrystal Waveguides

2003 ◽  
Vol 770 ◽  
Author(s):  
Nathanael Smith ◽  
Max J. Lederer ◽  
Marek Samoc ◽  
Barry Luther-Davies ◽  
Robert G. Elliman
Keyword(s):  
Probe Beam ◽  
Time Resolution ◽  
Pump Beam ◽  
Silicon Nanocrystals ◽  
Continuous Wave ◽  
Optical Gain ◽  
Optical Pump ◽  
Time Resolved ◽  
Pump Probe ◽  
Probe Measurements

AbstractOptical pump-probe measurements were performed on planar slab waveguides containing silicon nanocrystals in an attempt to measure optical gain from photo-excited silicon nanocrystals. Two experiments were performed, one with a continuous-wave probe beam and a pulsed pump beam, giving a time resolution of approximately 25 ns, and the other with a pulsed pump and probe beam, giving a time resolution of approximately 10 ps. In both cases the intensity of the probe beam was found to be attenuated by the pump beam, with the attenuation increasing monotonically with increasing pump power. Time-resolved measurements using the first experimental arrangement showed that the probe signal recovered its initial intensity on a time scale of 45-70 μs, a value comparable to the exciton lifetime in Si nanocrystals. These data are shown to be consistent with an induced absorption process such as confined carrier absorption. No evidence for optical gain was observed.

scholarly journals Mass-resolved electronic circular dichroism ion spectroscopy

Science ◽  
2020 ◽  
Vol 368 (6498) ◽  
pp. 1465-1468 ◽  
Author(s):  
Steven Daly ◽  
Frédéric Rosu ◽  
Valérie Gabelica
Keyword(s):  
Circular Dichroism ◽  
Three Dimensional ◽  
Polarized Light ◽  
Negative Ions ◽  
Data Interpretation ◽  
Electronic Circular Dichroism ◽  
Circularly Polarized Light ◽  
Chiral Compounds ◽  
Electron Photodetachment ◽  
Circular Dichroïsm

DNA and proteins are chiral: Their three-dimensional structures cannot be superimposed with their mirror images. Circular dichroism spectroscopy is widely used to characterize chiral compounds, but data interpretation is difficult in the case of mixtures. We recorded the electronic circular dichroism spectra of DNA helices separated in a mass spectrometer. We studied guanine-rich strands having various secondary structures, electrosprayed them as negative ions, irradiated them with an ultraviolet nanosecond optical parametric oscillator laser, and measured the difference in electron photodetachment efficiency between left and right circularly polarized light. The reconstructed circular dichroism ion spectra resembled those of their solution-phase counterparts, thereby allowing us to assign the DNA helical topology. The ability to measure circular dichroism directly on biomolecular ions expands the capabilities of mass spectrometry for structural analysis.

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