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High resolution time- and angle-resolved photoemission spectroscopy with 11 eV laser pulses
摘要： Performing time- and angle-resolved photoemission (tr-ARPES) spectroscopy at high momenta necessitates extreme ultraviolet laser pulses, which are typically produced via high harmonic generation (HHG). Despite recent advances, HHG-based setups still require large pulse energies (from hundreds of μJ to mJ) and their energy resolution is limited to tens of meV. Here, we present a novel 11 eV tr-ARPES setup that generates a flux of 5 × 1010 photons/s and achieves an unprecedented energy resolution of 16 meV. It can be operated at high repetition rates (up to 250 kHz) while using input pulse energies down to 3 μJ. We demonstrate these unique capabilities by simultaneously capturing the energy and momentum resolved dynamics in two well-separated momentum space regions of a charge density wave material ErTe3. This novel setup offers the opportunity to study the non-equilibrium band structure of solids with exceptional energy and time resolutions at high repetition rates.
关键词： energy resolution,time- and angle-resolved photoemission spectroscopy,HHG,tr-ARPES,charge density wave,high repetition rates,high harmonic generation,ErTe3,11 eV laser pulses
更新于2025-09-23 15:19:57
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Coherent Coupled-Mode Phonon Emission in a Photoexcited Charge-Density-Wave System
摘要： Photoexcitation the quasi-one-dimensional of charge-density-wave (CDW) system, blue bronze (K0.3MoO3), with near-infrared femtosecond pulses, results in both a low-frequency, broadband THz surface emission from the photo-Dember effect, and a narrow-band emission from a TO phonon doublet centered at 1.5 THz below ~100 K in the CDW state. The polarization dependence of the phonon emission leads us to propose a surface-field/quadrupole excitation mechanism, distinct from the typical mechanisms for phonon emission in other materials. A coupled-oscillator model with a transient suppression of the mode coupling can reproduce the detailed temporal and spectral characteristics of the emission.
关键词： charge-density-wave,photo-Dember effect,coupled-oscillator model,THz emission,coherent phonon emission
更新于2025-09-16 10:30:52
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Interplay of structure and charge order revealed by quantum oscillations in thin films of
摘要： The discovery of quantum oscillations in hole- and electron-doped cuprate families has underscored the importance of the Fermi surface in cuprate superconductivity. While the observed quantum oscillations in both families have revealed the presence of reconstructed Fermi surfaces, there remains an important distinction between the two. In hole-doped cuprates the oscillations are thought to arise from the effects of a charge density wave, while in the electron-doped cuprates it is thought that these oscillations occur from an antiferromagnetically reconstructed Fermi surface, despite the fact that the oscillations are observed in overdoped compounds, far from the putative antiferromagnetic critical point. In this work we study thin films of Pr2CuO4±δ, whose apparent doping can be finely tuned by annealing, allowing studies of quantum oscillations in samples straddling the critical point. We show that even though there is a mass enhancement of the quasiparticles, there are only small changes to the Fermi surface itself, suggesting that charge order is a more likely origin, with electronic correlations that are strongly dependent on the structural parameters.
关键词： antiferromagnetic critical point,Fermi surface,cuprate superconductivity,quantum oscillations,charge density wave
更新于2025-09-12 10:27:22
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Electrically tuning many-body states in a Coulomb-coupled InAs/InGaSb double layer
摘要： We study the transport properties of an electron-hole double layer consisting of barrier-separated InAs/InGaSb quantum wells. We focus on measurements of four-terminal resistivity of a Hall-bar sample as a function of electron (n) and hole (p) density, that are being tuned by a pair of top and bottom gates. In zero magnetic ?eld, we clearly observe an insulating phase which occurs at a charge neutral point, below a critical carrier density n = p < 1 × 1011 cm?2. This phase is characterized by a narrow and thermally activated resistance peak and an anomalous Hall resistance. This observation reinforces our previous ?nding of an excitonic insulator. Remarkably, when the layer densities are being tuned into imbalance, here p (cid:2) n, a broader resistance peak emerges. We discuss this phase with respect to a possible (theoretically predicted) charge density wave ground state. Both phases can persist above ～25 K, indicating robust correlations in the electron-hole double layers.
关键词： electron-hole double layer,exciton condensation,InAs/InGaSb quantum wells,quantum spin Hall effect,charge density wave
更新于2025-09-12 10:27:22
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Quantitative Mapping of the Charge Density in a Monolayer of MoS <sub/>2</sub> at Atomic Resolution by Off-Axis Electron Holography
摘要： The electric potential, electric field and charge density of a monolayer of MoS2 has been quantitatively measured at atomic scale resolution. This has been performed by off-axis electron holography using a double aberration-corrected transmission electron microscope operated at 80 kV and a low electron beam current density. Using this low dose rate and acceleration voltage, the specimen damage is limited during imaging. In order to improve the sensitivity of the measurement, series of holograms have been acquired. Instabilities of the microscope such as the drifts of the specimen, biprism and optical aberrations during the acquisition have been corrected by data processing. Phase images of the MoS2 monolayer have been acquired with a sensitivity of 2π/698 rad associated to a spatial resolution of 2.4 ?. The improvement in the signal-to-noise ratio allows the charge density to be directly calculated from the phase images using Poisson’s equation. Density functional theory simulations of the potential and charge density of this MoS2 monolayer were performed for comparison to the experiment. The experimental measurements and simulations are consistent with each other and notably, the charge density in a sulphur mono-vacancy (VS) site is shown.
关键词： MoS2,high-resolution,charge density,electric potential,electric field,electron holography,sulphur vacancy
更新于2025-09-12 10:27:22
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Tailoring and Modifying an Organic Electron Acceptor toward the Cathode Interlayer for Highly Efficient Organic Solar Cells
摘要： With the rapid advance of organic photovoltaic materials, the energy level structure, active layer morphology, and fabrication procedure of organic solar cells (OSCs) are changed significantly. Thus, the photoelectronic properties of many traditional electrode interlayers have become unsuitable for modifying new active layers; this limits the further enhancement in OSC efficiencies. Herein, a new design strategy of tailoring the end-capping unit, ITIC, to develop a cathode interlayer (CIL) material for achieving high power conversion efficiency (PCE) in OSCs is demonstrated. The excellent electron accepting capacity, suitable energy level, and good film-forming ability endow the S-3 molecule with an outstanding electron extraction property. A device with S-3 shows a PCE of 16.6%, which is among the top values in the field of OSCs. More importantly, it is demonstrated that the electrostatic potential difference between the CIL molecule and the polymer donor plays a crucial role in promoting exciton dissociation at the CIL/active layer interface, contributing to additional charge generation; this is crucial for enhancement of the current density. The results of this work not only develop a new design strategy for high-performance CIL, but also demonstrate a reliable approach of density functional theory (DFT) calculation to predict the effect of the CIL chemical structure on exciton dissociation in OSCs.
关键词： organic electron acceptors,cathode interlayers,charge density difference,organic solar cells,high efficiency
更新于2025-09-12 10:27:22
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Imaging Chladni figure of plasmonic charge density wave in real space
摘要： The future photonic age largely depends on our ability to manipulate optical waves in confined systems. Particularly, understanding the behavior of plasmonic charge density wave (p-CDW) in optical resonators is vital for engineering 2D plasmonic devices. In this study, the standing p-CDW on the surface of a gold triangle resonator is examined through diffraction limited all-optical far field power loss microscopy. The scattering light map captured by this microscopy, named plasmonic Chladni figure, is directly proportional to the entire in-plane photonic local density of state. The theoretical model of plasmonic Chladni figure proposed in this study is related to the 2D standing p-CDW node pattern, which is similar to the mechanical Chladni but follows a special node selection rule. Investigating the plasmonic Chladni phenomenon provides an in-depth understanding of fundamental plasmonic physics, plasmonic chemistry, and presents various possibilities for plasmonic application, such as 2D dimensional SPP waveguide, plasmonic computing, hot electron based chemistry, light energy harvest and so on.
关键词： photonic local density of states,standing wave,electrochemical charging,plasmonic resonator,plasmonic charge density wave,plasmonic Chladni figure
更新于2025-09-11 14:15:04
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Trimer bonding states on the surface of the transition-metal dichalcogenide
摘要： We report a comprehensive study on the surface structural and electronic properties of TaTe2 at room temperature. The surface structure was investigated using both low energy electron diffraction intensity versus voltage and density functional theory calculations. The relaxed structures obtained from the two methods are in good agreement, which is very similar to the bulk, maintaining double zigzag trimer chains. The calculated density of states indicates that such structure originates from the trimer bonding states of the Ta dxz and dxy orbitals. This work will further provide new insights towards the understanding of the charge density wave phase transition in TaTe2 at low temperature.
关键词： surface structure,low energy electron diffraction,density functional theory,charge density wave,TaTe2
更新于2025-09-10 09:29:36
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Stability of the light-induced hidden charge density wave state within the phase diagram of
摘要： The femtosecond transient optical spectroscopy is employed to study the relaxation dynamics of the equilibrium and hidden metastable charge-density-wave states in single crystals of 1T-TaS2?xSex as a function of the Se doping x. Similar to pristine 1T-TaS2, the transition to a hidden phase is observed at low temperature after a quench with a single 50 fs laser pulse, in the commensurate Mott phase up to x = 0.6. The photo-induced hidden-phase formation is accompanied by a notable change in the coherent phonon spectra, and particularly the collective amplitude mode. While the temperature stability of the hidden phase is only slightly dependent on the Se content, the creation-threshold ?uence strongly increases with Se content from 1 to ～4 mJ/cm2, which is attributed predominantly to the change in optical absorption coef?cient at the laser excitation wavelength, and not an increased barrier of the hidden state with increasing Se.
关键词： hidden phase,charge-density-wave states,1T-TaS2?xSex,coherent phonon spectra,femtosecond transient optical spectroscopy
更新于2025-09-10 09:29:36
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Gauge invariance and origin independence of electronic charge density and current density induced by optical fields
摘要： Expressions for the first-order polarization charge density ρ(1) and current density J(1) induced in a molecule by a monochromatic plane wave, obtained by time-dependent quantum mechanical perturbation theory, have been investigated to assess their gauge invariance and independence of the coordinate system in passive and active translations. The conditions arrived at show that, within the (long wavelengths) dipole approximation, only the electric contributions to these densities are needed to rationalize the phenomenology. To the next higher quadrupole approximation, assuming that the magnetic field and the electric field gradient are uniform over the molecular dimensions, corresponding contributions to ρ(1) and J(1) are considered. It has been found that total densities are independent of the origin, whereas the contributions from electric and magnetic fields are not separately invariant. A magnetic contribution to J(1), which is by itself origin independent, can be defined by means of an approach based on continuous translation of the origin of the coordinate system.
关键词： time-dependent perturbation theory,origin independence,quadrupole approximation,current density,optical fields,gauge invariance,dipole approximation,electronic charge density
更新于2025-09-09 09:28:46