629 research outputs found
Effects of impurities on Tamm-like lanthanide-metal surface states
The effects of isolated residual-gas adsorbates on the local electronic
structure of the Dy(0001) surface were spatially mapped by scanning tunneling
microscopy and spectroscopy at 12 K. Less than 15 A away from an adsorbate, a
strong reduction of the intensity and a significant increase of the width of
the majority component of the surface state due to impurity scattering were
observed, with essentially no change of the minority component; this reflects a
high lateral localization of the Tamm-like surface state. Furthermore, an
adsorbate-induced state was found that behaves metastable.Comment: 5 pages, 4 figures, accepted as Brief Report for Physical Review
Ultrafast Angle-Resolved Photoemission Spectroscopy of Quantum Materials
Techniques in time- and angle-resolved photoemission spectroscopy have
facilitated a number of recent advances in the study of quantum materials. We
review developments in this field related to the study of incoherent
nonequilibrium electron dynamics, the analysis of interactions between
electrons and collective excitations, the exploration of dressed-state physics,
and the illumination of unoccupied band structure. Future prospects are also
discussed.Comment: 7 pages, 6 figure
Broadband THz study of excitonic resonances in the high-density regime
We report the first terahertz study of the intra-excitonic 1s-2p transition
at high excitation densities in GaAs/AlGaAs quantum wells. A strong shift,
broadening, and ultimately the disappearance of this resonance occurs with
increasing density, after ultrafast photoexcitation at the near-infrared
exciton line. Densities of excitons and unbound electron-hole pairs are
followed quantitatively using a model of the composite terahertz dielectric
response. Comparison with near-infrared absorption changes reveals a
significantly enhanced energy shift and broadening of the intra-excitonic
resonance.Comment: 4 pages, 4 figure
Broadband electromagnetic response and ultrafast dynamics of few-layer epitaxial graphene
We study the broadband optical conductivity and ultrafast carrier dynamics of
epitaxial graphene in the few-layer limit. Equilibrium spectra of nominally
buffer, monolayer, and multilayer graphene exhibit significant terahertz and
near-infrared absorption, consistent with a model of intra- and interband
transitions in a dense Dirac electron plasma. Non-equilibrium terahertz
transmission changes after photoexcitation are shown to be dominated by excess
hole carriers, with a 1.2-ps mono-exponential decay that reflects the
minority-carrier recombination time.Comment: 4 pages, 3 figures, final versio
Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases
We report a comprehensive experimental study and detailed model analysis of
the terahertz dielectric response and density kinetics of excitons and unbound
electron-hole pairs in GaAs quantum wells. A compact expression is given, in
absolute units, for the complex-valued terahertz dielectric function of
intra-excitonic transitions between the 1s and higher-energy exciton and
continuum levels. It closely describes the terahertz spectra of resonantly
generated excitons. Exciton ionization and formation are further explored,
where the terahertz response exhibits both intra-excitonic and Drude features.
Utilizing a two-component dielectric function, we derive the underlying exciton
and unbound pair densities. In the ionized state, excellent agreement is found
with the Saha thermodynamic equilibrium, which provides experimental
verification of the two-component analysis and density scaling. During exciton
formation, in turn, the pair kinetics is quantitatively described by a Saha
equilibrium that follows the carrier cooling dynamics. The terahertz-derived
kinetics is, moreover, consistent with time-resolved luminescence measured for
comparison. Our study establishes a basis for tracking pair densities via
transient terahertz spectroscopy of photoexcited quasi-two-dimensional
electron-hole gases.Comment: 14 pages, 8 figures, final versio
Surface-electronic structure of La(0001) and Lu(0001)
Most spectroscopic methods for studying the electronic structure of metal
surfaces have the disadvantage that either only occupied or only unoccupied
states can be probed, and the signal is cut at the Fermi edge. This leads to
significant uncertainties, when states are very close to the Fermi level. By
performing low-temperature scanning tunneling spectroscopy and ab initio
calculations, we study the surface-electronic structure of La(0001) and
Lu(0001), and demonstrate that in this way detailed information on the
surface-electronic structure very close to the Fermi energy can be derived with
high accuracy.Comment: 6 pages, 4 figures, 1 table submitted to PR
Introduction to the HICSS-55 Software Development for Mobile Devices, the Internet-of-Things, and Cyber-Physical Systems Minitrack
publishedVersio
- …