641 research outputs found
Chapter 1 THE WESTMINSTER MODEL AND THE UK POLITICAL SYSTEM BEFORE BREXIT
Westminster model; UK politics; Brexi
Exciton Control in a Room-Temperature Bulk Semiconductor with Coherent Strain Pulses
The coherent manipulation of excitons in bulk semiconductors via the lattice
degrees of freedom is key to the development of acousto-optic and
acousto-excitonic devices. Wide-bandgap transition metal oxides exhibit
strongly bound excitons that are interesting for applications in the
deep-ultraviolet, but their properties have remained elusive due to the lack of
efficient generation and detection schemes in this spectral range. Here, we
perform ultrafast broadband deep-ultraviolet spectroscopy on anatase TiO
single crystals at room temperature, and reveal a dramatic modulation of the
exciton peak amplitude due to coherent acoustic phonons. This modulation is
comparable to those of nanostructures where exciton-phonon coupling is enhanced
by quantum confinement, and is accompanied by a giant exciton shift of 30-50
meV. We model these results by many-body perturbation theory and show that the
deformation potential coupling within the nonlinear regime is the main
mechanism for the generation and detection of the coherent acoustic phonons.
Our findings pave the way to the design of exciton control schemes in the
deep-ultraviolet with propagating strain pulses
Chapter 1 THE WESTMINSTER MODEL AND THE UK POLITICAL SYSTEM BEFORE BREXIT
Westminster model; UK politics; Brexi
Giant exciton Mott density in anatase TiO2
Elucidating the carrier density at which strongly bound excitons dissociate
into a plasma of uncorrelated electron-hole pairs is a central topic in the
many-body physics of semiconductors. However, there is a lack of information on
the high-density response of excitons absorbing in the near-to-mid ultraviolet,
due to the absence of suitable experimental probes in this elusive spectral
range. Here, we present a unique combination of many-body perturbation theory
and state-of-the-art ultrafast broadband ultraviolet spectroscopy to unveil the
interplay between the ultraviolet-absorbing two-dimensional excitons of anatase
TiO and a sea of electron-hole pairs. We discover that the critical density
for the exciton Mott transition in this material is the highest ever reported
in semiconductors. These results deepen our knowledge of the exciton Mott
transition and pave the route toward the investigation of the exciton phase
diagram in a variety of wide-gap insulators
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Elucidating Piezoelectricity and Strain in Monolayer MoS2 at the Nanoscale Using Kelvin Probe Force Microscopy
Strain engineering modifies the optical and
electronic properties of atomically thin transition metal dichalcogenides.
Highly inhomogeneous strain distributions in twodimensional
materials can be easily realized, enabling control of
properties on the nanoscale; however, methods for probing strain
on the nanoscale remain challenging. In this work, we characterize
inhomogeneously strained monolayer MoS2 via Kelvin probe force
microscopy and electrostatic gating, isolating the contributions of
strain from other electrostatic effects and enabling the measurement
of all components of the two-dimensional strain tensor on
length scales less than 100 nm. The combination of these methods
is used to calculate the spatial distribution of the electrostatic
potential resulting from piezoelectricity, presenting a powerful way
to characterize inhomogeneous strain and piezoelectricity that can be extended toward a variety of 2D materials.This research was primarily supported by the National Science
Foundation through the Center for Dynamics and Control of
Materials: an NSF MRSEC under Cooperative Agreement
Nos. DMR-1720595 and DMR-2308817. This work was
performed in part at the University of Texas Microelectronics
Research Center, a member of the National Nanotechnology
Coordinated Infrastructure (NNCI), which is supported by the
National Science Foundation (Grant ECCS-2025227), and
using the facilities and instrumentation supported by the
National Science Foundation through the Center for Dynamics
and Control of Materials: an NSF MRSEC under Cooperative
Agreement Nos. DMR-1720595 and DMR-2308817 and NSF
Major Research Instrumentation (MRI) program DMR-
2019130. E.B. acknowledges support from the National
Science Foundation under grant DMR-2308817 (X.P.) and
the Robert A. Welch Foundation under grant F-2092-
20220331 (F.Y.G.).Center for Dynamics and Control of Material
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