Insensitivity of spin dynamics to the orbital angular momentum transferred from twisted light to extended semiconductors

Abstract

We study the spin dynamics of carriers due to the Rashba interaction in semiconductor quantum disks and wells after excitation with light with orbital angular momentum. We find that although twisted light transfers orbital angular momentum to the excited carriers and the Rashba interaction conserves their total angular momentum, the resulting electronic spin dynamics is essentially the same for excitation with light with orbital angular momentum l = +|l| and l = −|l|. The differences between cases with different values of |l| are due to the excitation of states with slightly different energies and not to the different angular momenta per se, and vanish for samples with large radii where a k-space quasi-continuum limit can be established. These findings apply not only to the Rashba interaction but also to all other envelope-function approximation spin-orbit Hamiltonians like the Dresselhaus coupling.PACS numbers: 78.20. Bh, 78.20.Ls, 78.40.Fy, 42.50.Tx Light with orbital angular momentum (OAM), referred to as twisted light, is a relatively new field of research which has become increasingly popular [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] since Allen et al. showed how twisted light beams can be easily generated from conventional laser beams [18]. Recently, the theoretical foundation of the optical excitation of solids and nanostructures with twisted light has been established [19][20][21][22][23][24][25][26][27], and experimental studies with twisted light on semiconductors have been carried out [28,29].One motivation for such studies is the prospect of using the large amounts of angular momentum that twisted light can carry in order to control the spin dynamics of electrons, thus adding a flexible tool to the active field of spin control [30][31][32][33][34][35][36][37][38][39]. In this context two different mechanisms need to be distinguished. First, angular momentum as well as energy selection rules can lead to selective optical excitation of carriers with a preferred spin direction. This mechanism enables fast spin-selective preparation of states during the photoexcitation process and has recently been studied for strongly confined systems such as quantum dots [27] and quantum rings [23]. Secondly, the spin-orbit interaction-like the Rashba [40] and Dresselhaus [41] couplings in semiconductor structures-is expected to couple the OAM of carriers transferred from the twisted light [19,22] to their spin degree of freedom. This would provide a slower carrier spin control which would be dynamical and would remain active after the twisted light pulse.In this Letter, we study the spin dynamics of carriers in semiconductor quantum disks and wells excited with twisted light taking into account the Rashba spin-orbit interaction. Our central finding is that, rather unexpectedly, the spin dynamics of the photo-excited electrons differs only slightly after excitation with light with and without OAM in the limit of large quantum disks, becoming insensitive to the OAM content of the twisted light beam ...

Spin polarization of photoelectrons in GaAs excited by twisted photons

“…(2) of Ref. [18], that, as we show in our paper, leads to the insensitivity to optical OAM. The details of underlying approximations and assumptions are presented in [16].…”

“…Electron kinetics and currents generated by twisted light in conduction band were extensively studied by Quinteiro et al [15][16][17]. Authors in [18] further develop that approach to study spin dynamics and predict only slight differences due to the photon OAM, also in agreement with experiment [4]. In these references, the electron response was averaged over the beam profile, see Eq.…”

“…To the best of our knowledge, there were no prior calculations of electron polarization in semiconductors excited by OAM light. Semi-classical formalism for OAMlight photo-excitations in bulk semiconductor and semiconductor heterostructures was previously developed in [15][16][17][18], where electron kinetics in the conduction band has been addressed. In contrast to these previous studies, we focus on impact parameter dependence of the photo-excited electron states.…”

Narrow quantum rings with general Rashba and Dresselhaus spin-orbit interactions

“…Furthermore, the injection of angular momentum via excitation with twisted light can provide a way to initialize the system in a finite-angular-momentum state. 2,3 Thus, the stage is set for an interesting angular momentum dynamics to take place, which could be studied and ultimately controlled for its use in quantum information processing. From a fundamental point of view, QR are an excellent scheme for studying spin-interference quantum mechanical effects.…”

Spin and charge transport induced by a twisted light beam on the surface of a topological insulator

“…Recently, magneto-optical effects and optical excitation using a twisted light beam, whose phase is twisted around the direction of the propagation of light, have been theoretically predicted [15][16][17][18][19][20] and experimentally carried out 21,22 . A twisted light has the following two intriguing properties distinct from a plane wave 23 .…”