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Excitation transfer
Excitation transfer is a collision process in which an excited atom or molecule passes its excitation energy to a partner, distinct from the collisionless optical mechanism resonance energy transfer.
Excitation–emission matrix fluorescence spectroscopy
Excitation–emission matrix fluorescence spectroscopy, or fluorescence EEM, measures fluorescence intensity over excitation and emission wavelengths to produce 3D molecular fingerprints, routine in water quality analysis of dissolved organic matter.
Excited state
An excited state is a quantum state of an atom or molecule with energy higher than the ground state, reached by absorbing a discrete amount of energy.
Excited-state iminium and enamine catalysis
Excited-state iminium and enamine catalysis is a branch of asymmetric organocatalysis in which visible light promotes chiral iminium or enamine intermediates to excited states, unlocking radical reactions.
Excited-state transition-metal catalysis
Excited-state transition-metal catalysis is homogeneous catalysis in which a transition metal complex absorbs light and the excited state itself drives bond-making and bond-breaking, without a separate photosensitizer.
Exciton
An exciton is a bound electron–hole pair that acts as a chargeless quasiparticle in semiconductors and insulators, formed when light excites an electron across the bandgap.
Exciton Bose–Einstein condensation
Exciton Bose–Einstein condensation is the formation of a Bose–Einstein condensate from excitons, bound electron–hole pairs in photoexcited semiconductors. Proposed in 1962, it was directly observed in bulk copper oxide in 2022.
Exciton condensate
An exciton condensate is a Bose–Einstein condensate of excitons, charge-neutral electron–hole pairs bound by the Coulomb interaction, known for dissipationless energy transport and quantum Hall drag, first observed in semiconductor double quantum wells.
Exciton condensation
Exciton condensation is the formation of a coherent quantum state in which many bound electron-hole pairs, called excitons, occupy a single ground state like Bose-Einstein condensation.
Exciton condensation in electron-hole bilayers
Exciton condensation in electron-hole bilayers is a quantum state in which electrons bound to holes in a neighboring layer condense into a coherent superfluid-like ground state.
Exciton diffusion
Exciton diffusion is the random-walk spreading of bound electron–hole pairs through a semiconductor after light excitation, governing energy transport in 2D materials and organic semiconductors.
Exciton diffusion length
The exciton diffusion length is the average distance an exciton travels in a semiconductor before recombining, a key design parameter for organic solar cells and LEDs.
Exciton funneling
Exciton funneling is the directed transport of excitons, neutral electron-hole pairs, toward regions of lower energy created by strain gradients in atomically thin semiconductors like monolayer WSe₂.
Exciton funneling in van der Waals heterostructures
Exciton funneling in van der Waals heterostructures is the directed transport of excitons through stacks of atomically thin materials, driven by strain, electric fields, or dielectric patterning.
Exciton Mott transition
The exciton Mott transition is the density-driven ionization of bound excitons into a conducting electron-hole plasma, reached in 2D semiconductors like MoS2 and WSe2 at critical densities around 10^12 to 10^13 cm^-2.
Exciton polariton
An exciton polariton is a quasiparticle formed by strong coupling between an exciton and a photon, usually a photon confined in an optical microcavity, enabling polariton lasers and quantum fluids of light.
Exciton superfluidity
Exciton superfluidity is a quantum state of matter in which excitons, bound electron–hole pairs, condense and flow without viscosity, now studied mainly in van der Waals heterostructures.
Exciton transport
Exciton transport is the propagation of bound electron–hole pairs in semiconductors from where light generates them to where they recombine, underpinning solar cells and LEDs.
Exciton-polariton topological insulator
An exciton-polariton topological insulator is a photonic device in which polaritons in a honeycomb lattice of microcavities carry edge states that flow one way around defects, first demonstrated in 2018.
Exciton-polaron
An exciton-polaron is a quasiparticle in which an exciton, a bound electron-hole pair, is dressed by a Fermi sea of carriers or by lattice distortions in two-dimensional materials.
Exciton–magnon coupling
Exciton–magnon coupling is the interaction between an exciton and a magnon in a magnetic semiconductor, allowing optical excitations to read and manipulate spin information, most prominently in CrSBr.
Exciton–polariton condensation in perovskite nanowire cavities
Exciton–polariton condensation in perovskite nanowire cavities is the room-temperature formation of a coherent, laser-like state in which exciton–polariton quasiparticles condense in a perovskite nanowire that is both gain medium and cavity.
Excitonic insulator
An excitonic insulator is a state of matter in which bound electron–hole pairs, called excitons, form spontaneously and condense, first proposed by Nevill Mott in the early 1960s.
Exclusion limits in dark-matter searches
An exclusion limit in dark-matter searches is an upper bound, quoted at a stated confidence level, on a dark-matter particle's scattering cross-section as a function of its mass.
Exclusion process
An exclusion process is a stochastic interacting particle system where particles hop in continuous time on discrete sites, at most one per site; its asymmetric form, the ASEP, is a paradigm of non-equilibrium statistical physics.
Exclusive or
Exclusive or (XOR, exclusive disjunction) is the logical connective that yields true when exactly one of its two operands is true, written ⊕ or ⊻.
Exeligmos
The exeligmos (Greek ἐξελιγμός) is the triple Saros eclipse cycle, lasting about 54 years and 33 days, after which eclipses recur at nearly the same longitude and local time.
Exemestane
Exemestane, sold under the brand name Aromasin, is an irreversible steroidal aromatase inhibitor that treats hormone receptor-positive breast cancer in postmenopausal women, FDA-approved in 1999.
Exendin-4
Exendin-4 is a 39-amino-acid peptide found in Gila monster venom that acts as a long-lasting GLP-1 receptor agonist and became the basis for the diabetes drug exenatide, approved in 2005.
Exergy
Exergy, also called available energy or availability, is a thermodynamic property measuring the maximum useful work obtainable from a system as it reaches equilibrium with a reference environment.