Ref HAL: hal-01631138_v1
DOI: 10.1103/PhysRevLett.119.113902
WoS: WOS:000410897100007
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18 Citations
Résumé:

The spontaneous emergence of vector vortex beams with non-uniform polarization distribution is reported in a vertical-cavity surface-emitting laser with frequency-selective feedback. Anti-vortices with a hyperbolic polarization structure and radially polarized vortices are demonstrated. They exist close to and partially coexist with vortices with uniform and non-uniform polarization distributions characterized by four domains of pairwise orthogonal polarization. These vector vortices are argued to have soliton-like properties. Independently of this interpretation, the novel way of generating these nontrivial structures in a remarkably simple VCSEL system is regarded to be interesting and potentially beneficial for other experiments utilizing non-uniform polarization structures.

Ref HAL: hal-01629354_v1
Ref Arxiv: 1706.02528
Ref. & Cit.: NASA ADS
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Résumé:

We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalisation. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered statesfor high fidelity spin-photon interfaces.

Commentaires: 7 pages, 4 figures

Ref HAL: hal-01621240_v1
DOI: 10.1103/PhysRevB.96.165304
WoS: WOS:000412747900006
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1 Citation
Résumé:

We demonstrate theoretically that the presence of holes, either resident or photocreated, in diluted magnetic quantum wells accelerates the spin relaxation of electrons via a mechanismwhich has been previously overlooked. This effect is due to the spin correlations, which establish between magnetic ions coupled via hole-mediated Ruderman-Kittel-Kasuya-Yoshida interactions in the paramagnetic phase. As a consequence, the electron spin relaxation becomes temperature and hole density dependent, in contrast to existing theories. Our theory qualitatively reproduces the increase of the electron spin relaxation rate with pump power observed in n-doped CdMnTe magnetic quantum wells [Ben Cheikh et al., Phys. Rev. B 88, 201306 (2013)]. It also predicts a decrease of the spin relaxation rate with temperature, as observed, although not in the same temperature range.

Ref HAL: hal-01619882_v1
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Résumé:

We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system in semiconductors and apply it to study nuclear spin thermodynamics in GaAs microcavities. The nuclear spin system is found to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interactionthat was earlier reported to disrupt nuclear spin thermalisation [2]. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered states for high fidelity spin-photon interfaces.References[1] A. S. Oja, O. V. Lounasmaa, Rev. Mod. Phys 69, 1 (1997).[2] P. Maletinsky, M. Kroner, A. Imamoglu, Nat. Phys 5, 407 (2009).

Ref HAL: hal-01577957_v2
DOI: 10.1103/PhysRevB.96.085404
WoS: WOS:000406752500006
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3 Citations
Résumé:

We measure the spin-resolved transport of dipolar excitons in a biased GaAs double quantum well structure. From these measurements we extract both spin lifetime and mobility of the excitons. We find that below a temperature of 4.8K there is a sharp increase in the spin lifetime of the excitons, together with a sharp reduction in their mobility. Below a critical power the spin lifetime increases with increasing mobility and density, while above the critical power the opposite trend is observed. We interpret this transition as evidence of the interplay between two different spin dephasing mechanisms: at low mobility the dephasing is dominated by the hyperfine interaction with the lattice nuclei spins, while at higher mobility the spin-orbit interaction dominates and a Dyakonov-Perel spin relaxation takes over. The excitation power and temperature regime where the hyperfine interaction induced spin dephasing is observed correlates with the regime where a dark dipolar quantum liquid was reported recently on a similar sample.

Ref HAL: hal-01576088_v1
DOI: 10.3390/app7050442
WoS: WOS:000404449000010
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1 Citation
Résumé:

The objective of this paper is to summarize the results obtained for the state of polarization in the emission of a vertical-cavity surface-emitting laser with frequency-selective feedback added. We start our research with the single soliton, this situation presents two perpendicular main orientations, connected by a hysteresis loop. In addition, we also find the formation of a ring shaped intensity distribution, the vortex state, that shows two homogeneous states of polarization with very close values to those find in the soliton. For both cases above, the study shows the spatially resolved value of the orientation angle. It's important to remark too the appearance of a non negligible amount of circular light that gives vectorial character to all the different emissions investigated.

Ref HAL: hal-01562859_v1
DOI: 10.1103/PhysRevB.95.245209
WoS: WOS:000404020500004
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5 Citations
Résumé:

In III-V semiconductors it was shown theoretically that under optical cooling the nuclear-spin polaron bound to neutral donors would form below some critical nuclear-spin temperature Tc [Merkulov, Phys. Solid State 40, 930 (1998)]. The predicted critical behavior is a direct consequence of the use of the mean-field approximation. It is known however that in any finite-size system a critical behavior must be absent. Here we develop a model of the optically cooled nuclear polaron, which goes beyond the mean-field approximation. An expression of the generalized free energy of the optically cooled nuclear polaron, valid for a finite, albeit large, number of spins, is derived. This model permits us to describe the continuous transition from the fluctuation dominated regime to the collective regime, as the nuclear-spin temperature decreases. It is shown that due to the finite number of nuclear spins involved in the polaron, the critical effects close to Tc are smoothed by the spin fluctuations. Particularly, instead of a divergence, the nuclear-spin fluctuations exhibit a sharp peak at Tc, before being depressed well below Tc. Interestingly, the formation of the nuclear polaron can, in certain conditions, boost the nuclear polarization beyond the value obtained solely by optical pumping. Finally, we suggest that the nuclear polaron could be detected by spin noise spectroscopy or via its superparamagnetic behavior.