Engineering of cooling mechanisms is a bottleneck in nanoelectronics.Whereas thermal exchanges in diffusive graphene are mostly driven by defect assisted acoustic phonon scattering, the case of high-mobility graphene on hexagonal Boron Nitride (hBN) is radically different with a prominent contribution of remote phonons from the substrate. A bi-layer graphene on hBN transistor with local gate is driven in a regime where almost perfect current saturation is achieved by compensation of the decrease of the carrier density and Zener-Klein tunneling (ZKT) at high bias. Using noise thermometry, we show that this Zener-Klein tunneling triggers a new cooling pathway due to the emission of hyperbolic phonon polaritons (HPP) in hBN by out-of-equilibrium electron-hole pairs beyond the super-Planckian regime. The combination of ZKT-transport and HPP-cooling promotes graphene on BN transistors as a valuable nanotechnology for power devices and RF electronics.Energy relaxation in solids is provided by electron-electron interactions and phonon emission. The former give rise to Wiedemann-Franz (WF) heat conduction to the leads. In diffusive graphene, acoustic phonon emission is dominated by three-body electron-phononimpurity supercollisions (SC) at room temperature 1-4 . The case of high-mobility graphene, in spite of its technological interest, has been less investigated. The suppression of supercollisions and the vanishing of Wiedemann-Franz heat conduction at current saturation give rise to strongly out-of-equilibrium electron distributions where new cooling pathways become prominent. Intrinsic optical phonon (OP) cooling is one of those, it was reported at high density 5 and in suspended graphene 6,7 . Another relaxation mechanism involves interlayer Coulomb coupling in decoupled multilayer epitaxial graphene 8 . In supported graphene the coupling to remote polar phonons overwhelms that to OPs 9-12 . The case of hBN supported or encapsulated graphene is emblematic. Firstly, current saturation can be achieved at low fields E (see Ref. 13 ) opening access to the Zener Klein tunneling (ZKT) regime at high field 14,15 . Secondly, hBN is a uniaxial dielectric that sustains hyperbolic phonon-polaritons (HPPs) [16][17][18][19][20][21][22] in the two Reststrahlen (RS) bands hΩ I = 90-100 meV and hΩ II = 170-200 meV. As a marked difference with SiO 2 surface modes, HPPs can efficiently radiate energy across the dielectric layer 17 , avoiding hot-phonon effects and making an efficient thermal bridge between the graphene channel and the metallic gate in nanodevices.

Nonequilibrium patterns in open systems are ubiquitous in nature, with examples as diverse as desert sand dunes, animal coat patterns such as zebra stripes, or geographic patterns in parasitic insect populations. A theoretical foundation that explains the basic features of a large class of patterns was given by Turing in the context of chemical reactions and the biological process of morphogenesis. Analogs of Turing patterns have also been studied in optical systems where diffusion of matter is replaced by diffraction of light. The unique features of polaritons in semiconductor microcavities allow us to go one step further and to study Turing patterns in an interacting coherent quantum fluid. We demonstrate formation and control of these patterns. We also demonstrate the promise of these quantum Turing patterns for applications, such as low-intensity ultra-fast all-optical switches.

We revisit Mandel's notion that the degree of coherence equals the degree of indistinguishability by performing Hong-Ou-Mandel- (HOM-)type interferometry with single photons elastically scattered by a cw resonantly driven excitonic transition of an InAs/GaAs epitaxial quantum dot. We present a comprehensive study of the temporal profile of the photon coalescence phenomenon which shows that photon indistinguishability can be tuned by the excitation laser source, in the same way as their coherence time. A new figure of merit, the coalescence time window, is introduced to quantify the delay below which two photons are indistinguishable. This criterion sheds new light on the interpretation of HOM experiments under cw excitation, particularly when photon coherence times are longer than the temporal resolution of the detectors. The photon indistinguishability is extended over unprecedented time scales beyond the detectors' response time, thus opening new perspectives to conducting quantum optics with single photons and conventional detectors.

We demonstrate time reversal of nuclear spin dynamics in highly magnetized dilute liquid 3 He-4 He mixtures through effective inversion of long-range dipolar interactions. These experiments, which involve using magic sandwich NMR pulse sequences to generate spin echoes, probe the spatiotemporal development of turbulent spin dynamics and promise to serve as a versatile tool for the study and control of dynamic magnetization instabilities. We also show that a repeated magic sandwich pulse sequence can be used to dynamically stabilize modes of nuclear precession that are otherwise intrinsically unstable. To date, we have extended the effective precession lifetimes of our magnetized samples by more than three orders of magnitude. Elementary treatments of nuclear magnetic resonance (NMR) ignore collective effects. Individual spin dynamics are assumed to be independent of the sample magnetization M, and are thus governed by linear differential equations. This approximation is justified for many -but certainly not all -practical applications. One of the most well known and pervasive counter examples is the phenomenon of radiation damping [1], in which the emf induced in the pickup coil by M drives a current; the magnetic field associated with this current in turn acts on M, driving it into alignment with the static field B 0 in a nonlinear manner. A less common but more insidious problem arises when the magnetic field produced by the magnetized sample becomes large enough to directly influence spin dynamics [2,3,4,5,6]. This leads to a rich variety of nonlinear effects that range from spectral clustering to precession instabilities and spin turbulence. The former arises when small-angle NMR tipping pulses are applied to the sample (generating small angular displacements of M from B 0 ), and is manifest by the spontaneous appearance of long-lived geometrydependent modes of coherent nuclear precession. The latter occurs when large-angle tipping pulses are employed, and involves an exponential growth in the complexity of spatially inhomogeneous magnetization patterns. Far from being mere curiosities, phenomena arising from nonlocal interactions (including the joint action of 'distant dipolar fields' and radiation damping [7,8]) threaten to limit (or profoundly alter) the operation of state-of-the-art highfield high-resolution NMR spectrometers. They are equally important for understanding the dynamics of polarized quantum fluids including Bose-Einstein condensates [9], superfluid 3 He [10, 11], degenerate 3 He-4 He mixtures [12], and two-dimensional H gases [13]. From yet another perspective, the collective effects induced by distant dipolar fields can be used to amplify weak spin precession signals [14] and to enhance the sensitivity of precision searches for CP-violating permanent electric dipole moments [5].Here we describe NMR time reversal experiments that -for the first time -shed light on the extent to which the deleterious effects of spin turbulence can be controlled or suppressed. Moreover, they lay the foundatio...

We report on the resonant optical pumping of the | ± 1⟩ spin states of a single Mn dopant in an InAs/GaAs quantum dot which is embedded in a charge tunable device. The experiment relies on a W scheme of transitions reached when a suitable longitudinal magnetic field is applied. The optical pumping is achieved via the resonant excitation of the central Λ system at the neutral exciton X(0) energy. For a specific gate voltage, the redshifted photoluminescence of the charged exciton X- is observed, which allows a nondestructive readout of the spin polarization. An arbitrary spin preparation in the | + 1⟩ or |-1⟩ state characterized by a polarization near or above 50% is evidenced.

The optical spin Hall effect (OSHE) is a transport phenomenon of exciton polaritons in semiconductor microcavities, caused by the polaritonic spin-orbit interaction, that leads to the formation of spin textures. In the semiconductor cavity, the physical basis of the spin orbit coupling is an effective magnetic field caused by the splitting of transverse-electric and transverse-magnetic (TE-TM) modes. The spin textures can be observed in the near field (local spin distribution of polaritons), and as light polarization patterns in the more readily observable far field. For future applications in spinoptronic devices, a simple and robust control mechanism, which establishes a one-to-one correspondence between stationary incident light intensity and far-field polarization pattern, is needed. We present such a control scheme, which is made possible by a specific double-microcavity design.The detection and manipulation of spins is an important part of science, in areas ranging from quantum computing, information, and spintronics 1 , to ubiquitous medical imaging techniques such as Magnetic Resonance Imaging (MRI). Much of the functionality of spin effects rests on the ability to control the spin dynamics through the application of external optical and/or magnetic fields. For example, in MRI spatial gradients of external magnetic fields control the spin precession, and in electron or nuclear spin-based quantum computing logical operations are performed using spatially or time-varying electromagnetic fields (e.g. Ref.1,2 ). Major research efforts have focused on photonic counterparts to magnetic spin systems, including the plasmonic spin Hall effect 3 , and, importantly, wide-ranging investigations of the spin orbit interactions of light 4-8 . All-optical spin systems combine the benefits of magnetic spin systems and their (sometimes relatively simple) spin dynamics with the highly developed technology of optical preparation and detection of polarization states (the optical analogue of spin).A promising semiconductor system is a microcavity containing semiconductor quantum wells, where spin states of exciton-polaritons can be created optically and the TE-TM splitting yields a spin-orbit interaction that can be described by an effective magnetic field. This, in turn, gives rise to a polaritonic spin Hall effect, the so-called optical spin Hall effect (OSHE) 9-14 . Since polaritons with different in-plane wave vectors experience different effective magnetic fields, an isotropic distribution of polaritons on a ring in wave vector space can lead to an anisotropic polarization texture or pattern, both in real (configuration) and wave vector space.Such polarization/spin textures have been found for excitations of linearly and circularly polarized polaritons in Ref.10 and 14 , respectively (structurally similar polarization/spin textures are also present in different physical systems, e.g. 15,16 ). The OSHE in wave vector space corresponds to that seen experimentally in far-field observations, which are particularly important ...

Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle-resolved photoemission spectroscopy (ARPES), the technique of choice to non-invasively probe the electronic band structure of a material. By means of a state-of-the-art ARPES setup with sub-micron spatial resolution, we have investigated a heterostructure composed of Bernal-stacked bilayer graphene (BLG) on hexagonal boron nitride and deposited on a graphite flake. By voltage biasing the latter, the electric field effect is directly visualized on the valence band as well as on the carbon 1s core level of BLG. The band gap opening of BLG submitted to a transverse electric field is discussed and the importance of intralayer screening is put forward. Our results pave the way for new studies that will use momentum-resolved electronic structure information to gain insight on the physics of materials submitted to the electric field effect.

High-mobility hexagonal boron nitride (hBN)/graphene/ hBN heterostructures are able to reach intrinsic limits of transport. Here, we investigate optoelectronic mixing, which is a demanding function combining efficient photodetection and fast carrier dynamics. Using such a heterostructure embedded in a coplanar waveguide, we obtain a record conversion efficiency of about −40 dB for frequencies up to 65 GHz. This performance is obtained at high doping in the photobolometric regime. We provide a microscopic model of the photodetection, which accurately describes the experimental observations, allows the assessment of the intrinsic limits of our device, and paves the way for device optimization by revealing the different mechanisms at play.