Ref HAL: hal-04608436_v1
Ref Arxiv: 2401.14357
DOI: 10.1103/PhysRevB.109.195431
Ref. & Cit.: NASA ADS
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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-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-04608461_v1
DOI: 10.1088/2058-9565/ad3f42
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Time-translation symmetry breaking is a mechanism for the emergence of non-stationary many-body phases, so-called time-crystals, in Markovian open quantum systems. Dynamical aspects of time-crystals have been extensively explored over the recent years. However, much less is known about their thermodynamic properties, also due to the intrinsic nonequilibrium nature of these phases. Here, we consider the paradigmatic boundary time-crystal system, in a finite-temperature environment, and demonstrate the persistence of the time-crystalline phase at any temperature. Furthermore, we analyze thermodynamic aspects of the model investigating, in particular, heat currents, power exchange and irreversible entropy production. Our work sheds light on the thermodynamic cost of sustaining nonequilibrium time-crystalline phases and provides a framework for characterizing time-crystals as possible resources for, e.g. quantum sensing. Our results may be verified in experiments, for example with trapped ions or superconducting circuits, since we connect thermodynamic quantities with mean value and covariance of collective (magnetization) operators.

Résumé:

We will 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. We show 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 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.

Ref HAL: hal-04523215_v1
Ref Arxiv: 2403.02279
Ref INSPIRE: 2765291
DOI: 10.48550/arXiv.2403.02279
Ref. & Cit.: NASA ADS
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We compare three available models of graphene conductivity: a non-local Kubo model, a local model derived by Fialkovsky, and finally a non-local Quantum Field Theory based (QFT-b) model. The first two models are extensively used in the nanophotonic community. All these models are not ab-initio since they contain phenomenological parameters (like chemical potential and/or mass gap parameters), and are supposed to provide coherent results since they are derived from the same starting Hamiltonian. While we confirm that the local model is a proper limit of the non-local Kubo model, we find some inconsistencies in the QFT-b model as derived and used in literature. In particular, differently from the Kubo model, the QFT-b model does not satisfy the required Gauge invariance, and as a consequence it shows a plasma-like behavior for the interband transversal conductivity at low frequencies instead of the expected behavior (an almost constant conductivity as a function of frequency $\omega$ with a gap for frequencies $\hbar\omega < \sqrt{(\hbar v_{F}q)^{2} + 4m^{2}}$). The inconsistencies of QFT-b model predictions are due to a non-correct regularization-scheme which allows for the gauge invariance violation. We show how to correctly regularize the QFT-b model in order to satisfy the gauge invariance and, once also losses are correctly included, we show that the Kubo and QFT-b model exactly coincide. Our finding can be of relevant interest for both theory predictions and experimental tests in both the nanophotonic and Casimir effect communities.

Ref HAL: hal-04608544_v1
PMID 38422611
Ref Arxiv: 2303.03115
DOI: 10.1088/1361-6528/ad2f1c
WoS: 001186617500001
Ref. & Cit.: NASA ADS
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We consider the system of two parallel sheets of graphene which are moving with relative parallel velocity v ⃗ and calculate the Casimir energy by using the scattering approach. We analyze in detail the normal (perpendicular to the planes) Casimir force for two systems—graphene/graphene and ideal metal/graphene. In the non-relativistic case v ≪ v F , the relative correction to the Casimir energy ( E v − E 0 ) / E 0 is proportional to the ( v / c ) 2 (the maximum value is 0.0033 for the gapeless case and v = v F ) for the first system, and it is zero up to the Fermi velocity v = v F for system ideal metal/graphene.

Ref HAL: hal-04608564_v1
DOI: 10.1103/PhysRevB.109.125105
WoS: 001234906800006
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Based on a tight-binding model for the electron system, we investigate the transfer of energy, momentum, and angular momentum mediated by electromagnetic fields among buckminsterfullerene (C$_{60}$) and graphene nanostrips. Our nonequilibrium Green's function approach enables calculations away from local thermal equilibrium where the fluctuation-dissipation theorem breaks down. For example, the forces between C$_{60}$ and current-carrying nanostrips are predicted. It is found that the presence of current enhances the van der Waals attractive forces. For two current-carrying graphene strips rotated at some angle, the fluctuational force and torque are much stronger at the nanoscale compared to that of the static Biot-Savart law.