A trion is a localized excitation which consists of three charged particles. A negative trion consists of two

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

s and one hole and a positive trion consists of two holes and one electron. The trion itself is a

quasiparticle In physics, quasiparticles and collective excitations are closely related emergent phenomena arising when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum. For exa ...

and is somewhat similar to an

exciton An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids. ...

, which is a complex of one electron and one hole. The trion has a ground

singlet state In quantum mechanics, a singlet state usually refers to a system in which all electrons are paired. The term 'singlet' originally meant a linked set of particles whose net angular momentum is zero, that is, whose overall spin quantum number s=0. A ...

(

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally ...

''S'' = 0) and an excited triplet state (''S'' = 1). Here singlet and triplet degeneracies originate not from the whole system but from the two identical particles in it. The half-integer spin value distinguishes trions from excitons in many phenomena; for example, energy states of trions, but not excitons, are split in an applied magnetic field. Trion states were predicted theoretically in 1958; they were observed experimentally in 1993 in CdTe/Cd_1−xZn_xTe quantum wells, and later in various other optically excited

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...

structures. There are experimental proofs of their existence in nanotubes supported by theoretical studies. Despite numerous reports of experimental trion observations in different semiconductor heterostructures, there are serious concerns on the exact physical nature of the detected complexes. The originally foreseen 'true' trion particle has a delocalized wavefunction (at least at the scales of several Bohr radii) while recent studies reveal significant binding from charged impurities in real semiconductor quantum wells. Trions have been observed in atomically thin two-dimensional (2D) transition-metal dichalcogenide semiconductors. In 2D materials the form of the interaction between charge carriers is modified by the nonlocal screening provided by the atoms in the layer. The interaction is approximately logarithmic at short range and of Coulomb 1/''r'' form at long range. The

diffusion Monte Carlo Diffusion Monte Carlo (DMC) or diffusion quantum Monte Carlo is a quantum Monte Carlo method that uses a Green's function to solve the Schrödinger equation. DMC is potentially numerically exact, meaning that it can find the exact ground state ener ...

method has been used to obtain numerically exact results for the binding energies of trions in 2D semiconductors within the effective mass approximation.

References

{{Authority control Spintronics Quasiparticles Quantum electronics