Multistability of a coherent spin ensemble in a semiconductor microcavity

Abstract

Coherent manipulation of spin ensembles is a key issue in the development of spintronics. In particular, multivalued spin switching may lead to new schemes of logic gating and memories. This phenomenon has been studied with atom vapours 30 years ago, but is still awaited in the solid state. Here, we demonstrate spin multistability with microcavity polaritons in a trap. Owing to the spinor nature of these light-matter quasiparticles and to the anisotropy of their interactions, we can optically control the spin state of a single confined level by tuning the excitation power, frequency and polarization. First, we realize high-efficiency power-dependent polarization switching. Then, at constant excitation power, we evidence polarization hysteresis and determine the conditions for realizing multivalued spin switching. Finally, we demonstrate an unexpected regime, where our system behaves as a high-contrast spin trigger. These results open new pathways to the development of advanced spintronics devices and to the realization of multivalued logic circuits. Spin manipulation is the object of an intense research activity in a great variety of solid-state systems [1][2][3] . Owing to significant advances in tunability and miniaturization, semiconductor nanostructures have turned into ideal laboratories to address spintronics challenges 4 . In this respect, microcavity polaritons hold great potential 5,6 . Arising from the normal-mode coupling between cavity photons and quantum-well excitons, polaritons behave as bosons and possess unique coherence properties that have led to the demonstration of Bose-Einstein condensation and superfluidity [7][8][9] . A great advantage of polaritons is the one-to-one correspondence between the polariton spin and the polarization of the emitted light. This allowed the observations of the optical spin Hall effect 10 , or of half-quantum vortices 11 , which have shown that polaritons exhibit remarkable spin carrier properties. Finally, recent realizations of optical bistability 12,13 and electrical injection in polariton diodes 14 allow the implementation of low-power polaritronic devices working at room temperature 15,16 . Spin multistability refers to the possibility for a system to present three or more stable spin states for a given excitation condition. It requires precise control of coherence and interactions and is therefore difficult to realize. The only successful studies of multistability with a spinor system were carried out with atomic vapours 30 years ago 17,18 . Its demonstration in the solid state would clearly lead to new schemes of spin-based logic devices 19,20 . Microcavity polaritons were recently predicted to be promising candidates to explore spin multistability 21 . This phenomenon rapidly emerged as an innovative solution for the design of spin memory elements 22 , and for the realization of logic gates based on the selective transport of spin-polarized polaritons 23,24 . Such developments first require an experimental demonstration of spin multistability in a pattern...

Polaritonic Feshbach resonance

“…The different excitonic content of both polarization states results in asymmetric spinor interactions. Such spinor interactions offer a wide range of effects and a very rich physics to explore in semiconductor microcavities [13][14][15][16][17][18] .In this work, we demonstrate a Feshbach resonance in a polariton semiconductor microcavity. Feshbach biexcitonic resonant scattering is investigated through spectrally resolved circularly polarized pump-probe spectroscopy on a III-V based microcavity (Methods).…”

“…The different excitonic content of both polarization states results in asymmetric spinor interactions. Such spinor interactions offer a wide range of effects and a very rich physics to explore in semiconductor microcavities [13][14][15][16][17][18] .…”

Compactons and bistability in exciton-polariton condensates

“…15 The bistability of coherent spin ensembles described in the two-mode approximation by the spinor Gross-Pitaevskii equation with an external pump has been reported too. 11 Under appropriate conditions bright solitons may form in semiconductor microcavities as predicted in Ref. 16 and observed in Ref.…”

“…[8][9][10][11][12][13] The theory of this effect was developed within the framework of different mean-field models based either on equations for the polariton occupation number, 9 where the fractions of excitons and cavity photons are connected through the Hopfield coefficients, 14 or on coupled equations for excitons and photons. 15 The bistability of coherent spin ensembles described in the two-mode approximation by the spinor Gross-Pitaevskii equation with an external pump has been reported too.…”

Optical bistability in electrically driven polariton condensates

“…Technological achievements have opened a route to the creation of polariton-based logic elements [17][18][19][20][21][22] and optical integrated circuits [23,24], which can, in principle, work at relatively high temperatures in wide-band-gap systems. Bistability [25,26] and multistability [27,28] allow for fast [29] and energy efficient switching in such integrated circuit architectures. Furthermore, the inherent memory effect comprised in the hysteresis can be straightforwardly exploited to create a polaritonic memory device as a key ingredient in a logic circuit.…”