Condensed Matter

The electronic behaviour in graphene under a flexural field with random height displacements, considered as pseudo-magnetic fields, is studied. General folded deformations (not necessarily random) were first studied, giving an expression for the zero energy modes. For Gaussian folded deformations, it is possible to use a Coulomb gauge norm for the fields allowing contact with previous work on the quantum Hall effect with random fields, showing that the density of states has a power law behaviour and that the zero energy modes wavefunctions are multifractal. This hints of an unusual electron velocity distribution. Also, an Aharonov-Bohm pseudo-effect is produced. For more general non-folded general flexural strain, is not possible to use a Coulomb gauge. However, a Random Phase Approximation (RPA) and the scheme of random matrix theory allows to tackle the problem. For Gaussian distributed fields, the spectrum presents an average gap and for some cases, a breaking of the particle-hole symmetry. Finally, for the case of Lévy distributed fields, nearly flat bands are seen due to strong electron localization.

The ability to shuttle coherently individual electron spins in arrays of quantum dots is a key procedure for the development of scalable quantum information platforms. It allows the use of sparsely populated electron spin arrays, envisioned to efficiently tackle the one- and two-qubit gate challenges. When the electrons are displaced in an array, they are submitted to site-dependent environment interactions such as hyperfine coupling with substrate nuclear spins. Here, we demonstrate that the electron multi-directional displacement in a 3?3 array of tunnel coupled quantum dots enhances the spin coherence time via the motional narrowing phenomenon. More specifically, up to 10 configurations are explored by the electrons to study the impact of the displacement on spin dynamics. An increase of the coherence time by a factor up to 10 is observed in case of fast and repetitive displacement. The physical mechanism responsible for the loss of coherence induced by displacement is quantitatively captured by a simple model and its implications on spin coherence properties during the electron displacement are discussed in the context of large-scale quantum circuits.

Casimir and electrostatic non-contact friction between two gold plates, and a gold tip and a gold plate, are calculated taking into account the contribution of the electrical double layer. It is shown that in an extreme-near field ( d<10 nm) the contribution from the electrical double layer leads to the enhancement of non-contact friction by many orders of magnitude in comparison to the result of the conventional theory without this contribution. Casimir and electrostatic friction dominate for short and large separations, respectively. The calculated electrostatic friction is in good agreement with experimental data. The results obtained open the way to detect the Casimir friction using Atomic Force Microscope.

The magneto-optic Kerr effect is a powerful tool for measuring magnetism in thin films at microscopic scales, as was recently demonstrated by the major role it played in the discovery of two-dimensional (2D) ferromagnetism in monolayer CrI 3 and Cr 2 Ge 2 Te 6 . These 2D magnets are often stacked with other 2D materials in van der Waals heterostructures on a SiO 2 /Si substrate, giving rise to thin-film interference. This can strongly affect magneto-optical measurements, but is often not taken into account in experiments. Here, we show that thin-film interference can be used to engineer the magneto-optical signals of 2D magnetic materials and optimize them for a given experiment or setup. Using the transfer matrix method, we analyze the magneto-optical signals from realistic systems composed of van der Waals heterostructures on SiO 2 /Si substrates, using CrI 3 as a prototypical 2D magnet, and hexagonal boron nitride (hBN) to encapsulate this air-sensitive layer. We observe a strong modulation of the Kerr rotation and ellipticity, reaching several tens to hundreds of milliradians, as a function of the illumination wavelength, and the thickness of the SiO 2 and layers composing the van der Waals heterostructure. Similar results are obtained in heterostructures composed by other 2D magnets, such as CrCl 3 , CrBr 3 and Cr 2 Ge 2 Te 6 . Designing samples for the optimal trade-off between magnitude of the magneto-optical signals and intensity of the reflected light should result in a higher sensitivity and shorter measurement times. Therefore, we expect that careful sample engineering, taking into account thin-film interference effects, will further the knowledge of magnetization in low-dimensional structures.

This erratum aims to correct 1) the wrong expressions, 2) some typographical errors, 3) some erroneous points made in discussion of the disparity of heat flux ratios between our full RPA model and the local conductivity model, and 4) the lower bound of the characteristic distance scale comparable to the graphene thermal length, appearing in the original paper, which might confuse or mislead readers. Collectively, they don't change the key physics we sought to present.

We design and investigate an experimental system capable of entering an electron transport blockade regime in which a spin-triplet localized in the path of current is forbidden from entering a spin-singlet superconductor. To stabilize the triplet a double quantum dot is created electrostatically near a superconducting lead in an InAs nanowire. The dots are filled stochastically with electrons of either spin. The superconducting lead is a molecular beam epitaxy grown Al shell. The shell is etched away over a wire segment to make room for the double dot and the normal metal gold lead. The quantum dot closest to the normal lead exhibits Coulomb diamonds, the dot closest to the superconducting lead exhibits Andreev bound states and an induced gap. The experimental observations compare favorably to a theoretical model of Andreev blockade, named so because the triplet double dot configuration suppresses Andreev reflections. Observed leakage currents can be accounted for by finite temperature. We observe the predicted quadruple level degeneracy points of high current and a periodic conductance pattern controlled by the occupation of the normal dot. Even-odd transport asymmetry is lifted with increased temperature and magnetic field. This blockade phenomenon can be used to study spin structure of superconductors. It may also find utility in quantum computing devices that utilize Andreev or Majorana states.

We have previously reported ferromagnetism evinced by a large hysteretic anomalous Hall effect in twisted bilayer graphene (tBLG). Subsequent measurements of a quantized Hall resistance and small longitudinal resistance confirmed that this magnetic state is a Chern insulator. Here we report that, when tilting the sample in an external magnetic field, the ferromagnetism is highly anisotropic. Because spin-orbit coupling is negligible in graphene such anisotropy is unlikely to come from spin, but rather favors theories in which the ferromagnetism is orbital. We know of no other case in which ferromagnetism has a purely orbital origin. For an applied in-plane field larger than 5 T , the out-of-plane magnetization is destroyed, suggesting a transition to a new phase.

We demonstrate the occurrence of nodal non-Hermitian (NH) phases featuring exceptional degeneracies in chiral-symmetric disordered quantum wires, where NH physics naturally arises from the self-energy in a disorder-averaged Green's function description. Notably, we find that at least two nodal points in the clean Hermitian system are required for exceptional points to be effectively stabilized upon adding disorder. We identify and study experimental signatures of our theoretical findings both in the spectral functions and in mesoscopic quantum transport properties of the considered systems. Our results are quantitatively corroborated by numerically exact simulations. The proposed setting provides a conceptually minimal framework for the realization and study of topological NH phases in quantum many-body systems.

We generalize the mean-field Hartree Fock theory of gapped electronic states at charge neutrality in bilayer graphene to thin films of rhombohedral graphite with up to thirty layers. For the ground state, which has an odd spatial parity within each spin-valley flavor and an antiferromagnetic arrangement of four flavors, the order parameter (the separation of bands at the valley center) saturates to a constant non-zero value as the layer number increases, whereas the band gap decreases with layer number. We take into account chiral symmetry breaking disorder in the form of random layer potentials and chiral preserving disorder in the form of random values of the interlayer coupling. The former reduces the magnitude of the mean band gap whereas the latter has a negligible effect, which is due to self-averaging within a film with a large number of layers. We determine the ground state in the presence of an individual stacking fault embedded within a film of rhombohedral graphite. For a Bernal stacking fault, the ground state is also an odd parity antiferromagnetic state, and the fault can be interpreted as introducing a small coupling between two independent sections of rhombohedral graphite. For a twin boundary stacking fault, however, the ground state is an even parity antiferromagnetic state, and the fault introduces stronger coupling across the system. In the presence of stacking faults, each individual rhombohedral section with m layers contributes a pair of low-energy flat bands producing a peak in the Berry curvature located at a characteristic m -dependent wave vector. For both types of stacking fault, the Chern number per spin-valley flavor for the filled valence bands in the ground state is equal in magnitude to the total number of layers divided by two, the same value as for pristine rhombohedral graphite.

In this review we discuss several fundamental processes taking place in semiconductor nanocrystals (quantum dots, QDs) when their electron subsystem interacts with electromagnetic (EM) radiation. The physical phenomena of light emission and EM energy transfer from a QD exciton to other electronic systems such as neighbouring nanocrystals and polarisable 3D (semi-infinite dielectric or metal) and 2D (graphene) materials are considered. The cases of direct (II-VI) and indirect (silicon) band gap semiconductors are compared. We also cover the relevant non-radiative mechanisms such as the Auger process, electron capture on dangling bonds and interaction with phonons. The emphasis is on explaining the underlying physics and illustrating it with calculated and experimental results in a comprehensive, tutorial manner.