Ref HAL: hal-04258279_v1
Ref Arxiv: 2307.06730
DOI: 10.1063/5.0167480
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Despite the considerable interest for antiferromagnets that appeared with the perspective of using them for spintronics, their experimental study, including the imaging of antiferromagnetic textures, remains a challenge. To address this issue, quantum sensors, and, in particular, the nitrogen-vacancy (NV) defects in diamond have become a widespread technical solution. We review here the recent applications of single NV centers to study a large variety of antiferromagnetic materials, from quantitative imaging of antiferromagnetic domains and non-collinear states, to the detection of spin waves confined in antiferromagnetic textures and the non-perturbative measurement of spin transport properties. We conclude with recent developments improving further the magnetic sensitivity of scanning NV microscopy, opening the way to detailed investigations of the internal texture of antiferromagnetic objects.

Ref HAL: hal-04248760_v1
DOI: 10.1088/1361-6528/acc3a2
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Nanoporous GaN layers were fabricated using selective area sublimation through a self-organized AlN nanomask in a molecular beam epitaxy reactor. The obtained pore morphology, density and size were measured using plan-view and cross-section scanning electron microscopy experiments. It was found that the porosity of the GaN layers could be adjusted from 0.04 to 0.9 by changing the AlN nanomask thickness and sublimation conditions. The room temperature photoluminescence properties as a function of the porosity were analysed. In particular, a strong improvement (>100) of the room temperature photoluminescence intensity was observed for porous GaN layers with a porosity in the 0.4–0.65 range. The characteristics of these porous layers were compared to those obtained with a Si$_x$ N$_y$ nanomask. Furthermore, the regrowth of p-type GaN on light emitting diode structures made porous by using either an AlN or a Si$_x$ N$_y$ nanomask were compared.

Ref HAL: hal-04237859_v1
DOI: 10.1021/acs.nanolett.3c02875
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In the room-temperature magnetoelectric multiferroic, BiFeO3, the non-collinear antiferromagnetic state is coupled to the ferroelectric order, opening applications for low-power electric-field-controlled magnetic devices. While several strategies have been explored to simplify the ferroelectric landscape, here we directly stabilize a single domain ferroelectric and spin cycloid state in epitaxial BiFeO3(111) thin films grown on orthorhombic DyScO3(011). Comparing with films grown on SrTiO3(111), we identify anisotropic in-plane strain as a powerful handle to tailor the single antiferromagnetic state. In this single domain multiferroic state, we establish the thickness limit of the coexisting electric and magnetic orders and directly visualize the suppression of the spin cycloid induced by the magnetoelectric interaction below the ultrathin limit of 1.4 nanometers. This as-grown single domain multiferroic configuration in BiFeO3 thin films opens an avenue both for fundamental investigations and for electrically-controlled non-collinear antiferromagnetic spintronics.

DOI: 10.1103/PhysRevA.108.042201
Résumé:

We study the heat transfer between N coupled quantum resonators with applied synthetic electric and magnetic fields realized by changing the resonator parameters by external drivings. To this end we develop two general methods, based on the quantum optical master equation and on the Langevin equation for N coupled oscillators where all quantum oscillators can have their own heat baths. The synthetic electric and magnetic fields are generated by a dynamical modulation of the oscillator resonance with a given phase. Using Floquet theory, we solve the dynamical equations with both methods, which allow us to determine the heat flux spectra and the transferred power. We apply these methods to study the specific case of a linear tight-binding chain of four quantum coupled resonators. We find that, in that case, in addition to a nonreciprocal heat flux spectrum already predicted in previous investigations, the synthetic fields induce here nonreciprocity in the total heat flux, hence realizing a net heat flux rectification.

Ref HAL: hal-04208789_v1
Ref Arxiv: 2304.12071
DOI: 10.1103/PhysRevLett.131.116902
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Ref HAL: hal-04204671_v1
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Ref HAL: hal-04196317_v1
Ref Arxiv: 2308.09559
Ref INSPIRE: 2689469
DOI: 10.1103/PhysRevB.108.235154
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We present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. Our analysis reveals that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time-reversal symmetry. Our findings introduce a novel mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.