Ref HAL: hal-03692457_v1
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We present a numerical approach for the solution of EM scattering from a dielectric cylinder partially covered with graphene. It is based on a classical Fourier-Bessel expan- sion of the fields inside and outside the cylinder to which we apply the ad-hoc boundary conditions in the presence of graphene. Due to the singular nature of the electric field at the ends of the graphene sheet, we introduce auxiliary boundary conditions to better take this reality into account. The result is a very simple and very efficient method allow- ing the study of diffraction from such structures.

Ref HAL: hal-03689421_v1
DOI: 10.1063/5.0091675
WoS: WOS:000793516000006
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We report on the growth of 2D layered indium selenide films on (0001)-oriented sapphire substrates by coevaporation. The θ − 2θ x-ray diffractograms reveal that the (00l) planes are preferentially oriented parallel to the substrate with a tendency to deviate from the 2D stacking as a function of the growth time. The ϕ-scans performed for the (107) and (10 10) orientations of the hexagonal (h) and rhombohedral (r) phases, respectively, reveal that both polytypes coexist in the epitaxial films. We show that the merging of the h-(100), r-(101), h-(101), and r-(102) lines results in different spectral shapes in the θ − 2θ scans according to samples, which gives qualitative information about the contribution of each polytype.

Ref HAL: hal-03684307_v1
DOI: 10.3390/cryst12060782
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The sp2-bonded layered compound boron nitride (BN) exists in more than a handful of different polytypes (i.e., different layer stacking sequences) with similar formation energies, which makes obtaining a pure monotype of single crystals extremely tricky. The co-existence of polytypes in a similar crystal leads to the formation of many interfaces and structural defects having a deleterious influence on the internal quantum efficiency of the light emission and on charge carrier mobility. However, despite this, lasing operation was reported at 215 nm, which has shifted interest in sp2- bonded BN from basic science laboratories to optoelectronic and electrical device applications. Here, we describe some of the known physical properties of a variety of BN polytypes and their performances for deep ultraviolet emission in the specific case of second harmonic generation of light.

Ref HAL: hal-03677973_v1
Ref Arxiv: 2105.08075
Ref INSPIRE: 2079933
DOI: 10.1103/PhysRevLett.128.177401
Ref. & Cit.: NASA ADS
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We investigate the magnetic field dependent photo-physics of individual Nitrogen-Vacancy (NV) color centers in diamond under cryogenic conditions. At distinct magnetic fields, we observe significant reductions in the NV photoluminescence rate, which indicate a marked decrease in the optical readout efficiency of the NV's ground state spin. We assign these dips to excited state level anti-crossings, which occur at magnetic fields that strongly depend on the effective, local strain environment of the NV center. Our results offer new insights into the structure of the NVs' excited states and a new tool for their effective characterization. Using this tool, we observe strong indications for strain-dependent variations of the NV's orbital g-factor, obtain new insights into NV charge state dynamics, and draw important conclusions regarding the applicability of NV centers for low-temperature quantum sensing.

Ref HAL: hal-03659802_v1
DOI: 10.1103/PhysRevLett.128.187201
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We report on the formation of topological defects emerging from the cycloidal antiferromagnetic order at the surface of bulk BiFeO3 crystals. Combining reciprocal and real-space magnetic imaging techniques, we first observe, in a single ferroelectric domain, the coexistence of antiferromagnetic domains in which the antiferromagnetic cycloid propagates along different wave vectors. We then show that the direction of these wave vectors is not strictly locked to the preferred crystallographic axes as continuous rotations bridge different wave vectors. At the junctions between the magnetic domains, we observe topological line defects identical to those found in a broad variety of lamellar physical systems with rotational symmetries. Our work establishes the presence of these magnetic objects at room temperature in the multiferroic antiferromagnet BiFeO3, offering new possibilities for their use in spintronics

Ref HAL: hal-03621717_v1
DOI: 10.1103/PhysRevX.12.011057
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Ref HAL: hal-03621796_v1
Ref Arxiv: 2203.13761
Ref. & Cit.: NASA ADS
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A giant built-in electric field in the growth direction makes excitons in wide GaN/(Al, Ga)N quantum wells spatially indirect even in the absence of any external bias. Significant densities of indirect excitons can accumulate in electrostatic traps imprinted in the quantum well plane by a thin metal layer deposited on top of the heterostructure. By jointly measuring spatially-resolved photoluminescence and photo-induced current, we demonstrate that exciton density in the trap can be controlled via an external electric bias, which is capable of altering the trap depth. Application of a negative bias deepens the trapping potential, but does not lead to any additional accumulation of excitons in the trap. This is due to exciton dissociation instigated by the lateral electric field at the electrode edges. The resulting carrier losses are detected as an increased photo-current and reduced photoluminescence intensity. By contrast, application of a positive bias washes out the electrode-induced trapping potential. Thus, excitons get released from the trap and recover free propagation in the plane that we reveal by spatially-resolved photoluminescence.

Commentaires: 12 pages, 14 figures