Ref HAL: hal-04600016_v1
Ref Arxiv: 2404.15069
Ref INSPIRE: 2780133
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Among the wealth of single fluorescent defects recently detected in silicon, the G center catches interest for its telecom single-photon emission that could be coupled to a metastable electron spin triplet. The G center is a unique defect where the standard Born-Oppenheimer approximation breaks down as one of its atoms can move between 6 lattice sites under optical excitation. The impact of this atomic reconfiguration on the photoluminescence properties of G centers is still largely unknown, especially in silicon-on-insulator (SOI) samples. Here, we investigate the displacement of the center-of-mass of the G center in silicon. We show that single G defects in SOI exhibit a multipolar emission and zero-phonon line fine structures with splittings up to $\sim1$ meV, both indicating a motion of the defect central atom over time. Combining polarization and spectral analysis at the single-photon level, we evidence that the reconfiguration dynamics are drastically different from the one of the unperturbed G center in bulk silicon. The SOI structure freezes the delocalization of the G defect center-of-mass and as a result, enables to isolate linearly polarized optical lines. Under above-bandgap optical excitation, the central atom of G centers in SOI behaves as if it were in a 6-slot roulette wheel, randomly alternating between localized crystal sites at each optical cycle. Comparative measurements in a bulk silicon sample and ab initio calculations highlight that strain is likely the dominant perturbation impacting the G center geometry. These results shed light on the importance of the atomic reconfiguration dynamics to understand and control the photoluminescence properties of the G center in silicon. More generally, these findings emphasize the impact of strain fluctuations inherent to SOI wafers for future quantum integrated photonics applications based on color centers in silicon.

Ref HAL: hal-04608436_v1
Ref Arxiv: 2401.14357
DOI: 10.1103/PhysRevB.109.195431
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We examine the near-field radiative heat transfer between finite-thickness planar fused silica slabs covered with graphene gratings, through the utilization of the Fourier modal method augmented with local basis functions (FMM-LBF), with focus on the lateral shift effect. To do so, we propose and validate a minor modification of the FMM-LBF theory to account for the lateral shift. This approach goes far beyond the effective medium approximation because this latter cannot account for the lateral shift. We show that the heat flux can exhibit significant oscillations with the lateral shift and, at short separation, it can experience up to a 60%-70% reduction compared to the aligned case. Such a lateral shift effect is found to be sensitive to the geometric factor d/D (separation distance to grating period ratio). When d/D>1 (realized through large separation or small grating period), the two graphene gratings see each other as an effective whole rather than in detail, and thus the lateral shift effect on heat transfer becomes less important. Therefore, we can clearly distinguish two asymptotic regimes for radiative heat transfer: the LSE (Lateral Shift Effect) regime, where a significant lateral shift effect is observed, and the non-LSE regime, where this effect is negligible. Furthermore, regardless of the lateral shift, the radiative heat flux shows a non-monotonic dependence on the graphene chemical potential. That is, we can get an optimal radiative heat flux (peaking at about 0.3eV chemical potential) by in situ modulating the chemical potential. This work has the potential to unveil new avenues for harnessing the lateral shift effect on radiative heat transfer in graphene-based nanodevices.

Ref HAL: hal-04587561_v1
Ref Arxiv: 2401.06589
DOI: 10.1103/PhysRevB.109.205302
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Bound states in the continuum (BICs) are of special interest in photonics due to their theoretically infinite radiative lifetime. In this work, we take a specific example (a structure composed of GaN and a TiO2 photonic crystal slab), showcasing how the interactions affect BICs. The photonic BIC hosted by the photonic crystal slab couples with the excitons of GaN to form a polaritonic BIC with a negative mass. This allows condensation to be reached with a low threshold in a structure suitable for electrical injection, paving the way for room-temperature polariton microdevices. We study in detail how the repulsive interaction between exciton-polaritons affects the condensate distribution in reciprocal space and, consequently, the condensate's overlap with the BIC resonance and, therefore, the condensate lifetime. We study an intrinsic contribution related to the formation of a bright soliton and the extrinsic contribution related to the interaction with an excitonic reservoir induced by spatially focused nonresonant pumping. We then study the peculiar dynamics of the condensation process in a BIC state for interacting particles using Boltzmann equations and hybrid Boltzmann–Gross-Pitaevskii equations. We find optimal conditions allowing one to benefit from the long lifetime of the BIC for polariton condensation in a real structure.

Résumé:

I'll review some open open problems in determination of the effective action for Calabi-Yau compactifications of type II string theory, and argue that their solution requires a combination of modularity and resurgence.

Ref HAL: hal-04608450_v1
DOI: 10.1016/j.jqsrt.2024.109051
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We investigate a bi-layer scheme for circularly polarized infrared thermal radiation. Our approach takes advantage of the strong anisotropy of low-symmetry materials such as β-Ga2O$_3$ and α-MoO$_3$. We numerically report narrow-band, high degree of circular polarization (over 0.85), thermal radiation at two typical emission frequencies related to the excitation of β-Ga$_2$O$_3$ optical phonons. Optimization of the degree of circular polarization is achieved by a proper relative tilt of the crystal axes between the two layers. Our simple but effective scheme could set the basis for a new class of lithography-free thermal sources for IR bio-sensing.

Ref HAL: hal-04582437_v1
DOI: 10.1111/ijfs.17192
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Summary In this study, a 4% (w/w) dispersion of a commercial patatin‐rich potato protein isolate (Po‐PI) was pressurised at 400 MPa up to 48 h at 20 °C. Protein aggregation induced by high‐pressure processing (HHP) was followed by dynamic light scattering, intrinsic fluorescence ( in‐situ or ex‐situ ) or SAXS analysis. Surface properties (surface hydrophobicity and interfacial properties) of the HHP‐induced aggregates were also investigated. A gradual dimer dissociation/protein unfolding was observed under pressure. Po‐PI exhibited a slow relaxation time under pressure. Long‐time HHP (>4 h) induced significant modification of the Po‐PI protein structure with partial non‐reversible unfolding. After 48 h of pressurisation at 400 MPa, large aggregates (160 nm) were obtained and a monomodal distribution in intensity and in number frequency was observed indicating a controlled aggregation. Up to 24 h of pressurisation at 400 MPa, intermediate states were obtained after high‐pressure release. SDS‐PAGE profiles showed that HHP‐induced aggregation of Po‐PI was driven by non‐covalent interactions. All high‐pressure processed dispersions displayed a higher surface hydrophobicity as compared to non‐treated Po‐PI. Po‐PI dispersion treated for 8 h at 400 MPa presented the lowest adsorption rate, the highest final surface tension and formed the most rigid interfacial film. Po‐PI showed resistance to moderate pressure levels (400 MPa) and long pressure application times were required to induce significant protein denaturation/aggregation (≥24 h) and to optimally modify its interfacial properties (8 h).

Ref HAL: hal-04580626_v1
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