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Exotic ordered ground states driven by electronic correlations are expected to be induced in monolayer graphene when doped to the Van Hove singularity. Such doping levels are reached by intercalating Gd in graphene on SiC(0001), resulting in a strong homogeneity and stability. The electronic spectrum now exhibits severe renormalizations. Flat bands develop which is driven by electronic correlations according to our theoretical studies. Due to strong electron-phonon coupling in this regime, polaron replica bands develop. Thus, interesting ordered ground states should be made accessible.

Graphene is a powerful playground for studying a plethora of quantum phenomena. One of the remarkable properties of graphene arises when it is strained in particular geometries and the electrons behave as if they were under the influence of a magnetic field. Previously, these strain-induced pseudomagnetic fields have been explored on the nano- and micrometer-scale using scanning probe and transport measurements. Heteroepitaxial strain, in contrast, is a wafer-scale engineering method. Here, we show that pseudomagnetic fields can be generated in graphene through wafer-scale epitaxial growth. Shallow triangular nanoprisms in the SiC substrate generate strain-induced uniform fields of 41 T. This enables the observation of strain-induced Landau levels at room temperature, as detected by angle-resolved photoemission spectroscopy, and confirmed by model calculations and scanning tunneling microscopy measurements. Our work demonstrates the feasibility of exploiting strain-induced quantum phases in two-dimensional Dirac materials on a wafer-scale platform, opening the field to new applications., Comment: Revised version as published in Science Advances

The patterns of reversible changes in the critical current and discrete current states of a structure in the form of a superconducting quantum interferometer shunted by superconducting inductance, as a result of passing an alternating transport current through the structure and applying an external alternating magnetic field simultaneously with a direct transport current, was established. A new type of discrete stationary state was discovered during the transition of the interferometer to the resistive state caused by the combined action of direct and alternating transport currents., Comment: 6 pages, 9 figures

This review article is a commemoration of the 30th anniversary of the discovery of YBa2Cu3O7-delta high-temperature superconductors (HTSCs). As a result of this discovery a family of (RE)Ba2Cu3O7-delta (RE stands for "rare earth") HTSCs has found great practical use. The review article consists of a brief history of how YBa2Cu3O7-delta was conceived and five sections describing the family of compounds: crystallography, phase diagrams, manufacturing techniques, main superconducting properties, and fields of application., Comment: 27 pages, 33 figures

A simple method has been developed for manufacturing a thin film superconducting quantum interferometer (SQI) with ultralow inductance (~10^-13 H). Current-voltage and voltage-field characteristics of the SQI are presented. The basic design equations are obtained and confirmed experimentally. The SQI has been used for the first time to determine the penetration depth of a magnetic field into a film of 50% In-50% Sn alloy., Comment: 5 pages, 5 gigures

The magnetic moment in the superconducting and normal state of a crystalline FeTe0.65Se0.35 superconductor, grown by the Bridgman's method with relatively high growth rate, was measured. The temperature and magnetic field dependences of magnetization and its relaxation time were determined. Studied crystal, being non-uniform due to high growth rate of 5 mm/h, exhibits smaller width of superconducting transition in comparison with an ideal crystal grown with velocity of 1 mm/h, and the difference in magnetic properties of crystals grown with various growth rate, related to their microstructure, is discussed., Comment: 9 pages, 6 figures

The issue concerning the nature and the role of microstructural inhomogeneities in iron chalcogenide superconducting crystals of FeTe0.65Se0.35 and their correlation with transport properties of this system was addressed. Presented data demonstrate that chemical disorder originating from the kinetics of the crystal growth process significantly influences the superconducting properties of an Fe-Te-Se system. Transport measurements of the transition temperature and critical current density performed for microscopic bridges allow us to deduce the local properties of a superconductor with microstructural inhomogeneities, and significant differences were noted. The variances observed in the local properties were explained as a consequence of weak superconducting links existing in the studied crystals. The results confirm that inhomogeneous spatial distribution of ions and small hexagonal symmetry nanoscale regions with nanoscale phase separation also seem to enhance the superconductivity in this system with respect to the values of the critical current density. Magnetic measurements confirm the conclusions drawn from the transport measurements., Comment: 20 pages, 5 figures

Electron-phonon coupling directly determines the stability of cooperative order in solids, including superconductivity, charge and spin density waves. Therefore, the ability to enhance or reduce electron-phonon coupling by optical driving may open up new possibilities to steer materials' functionalities, potentially at high speeds. Here we explore the response of bilayer graphene to dynamical modulation of the lattice, achieved by driving optically-active in-plane bond stretching vibrations with femtosecond mid-infrared pulses. The driven state is studied by two different ultrafast spectroscopic techniques. Firstly, TeraHertz time-domain spectroscopy reveals that the Drude scattering rate decreases upon driving. Secondly, the relaxation rate of hot quasi-particles, as measured by time- and angle-resolved photoemission spectroscopy, increases. These two independent observations are quantitatively consistent with one another and can be explained by a transient three-fold enhancement of the electron-phonon coupling constant. The findings reported here provide useful perspective for related experiments, which reported the enhancement of superconductivity in alkali-doped fullerites when a similar phonon mode was driven., Comment: 12 pages, 4 figures

Electronic devices based on graphene technology are catching on rapidly and the ability to engineer graphene properties at the nanoscale is becoming, more than ever, indispensable. Here, we present a new procedure of graphene functionalization on SiC(0001) that paves the way towards the fabrication of complex graphene electronic chips. The procedure resides on the well-known ion-implantation technique. The efficiency of the working principle is demonstrated by the intercalation of the epitaxial graphene layer on SiC(0001) with Bi atoms, which was not possible following standard procedures. Our results put forward the ion-beam lithography to nanostructure and functionalize desired graphene chips.

Direct and inverse Auger scattering are amongst the primary processes that mediate the thermalization of hot carriers in semiconductors. These two processes involve the annihilation or generation of an electron-hole pair by exchanging energy with a third carrier, which is either accelerated or decelerated. Inverse Auger scattering is generally suppressed, as the decelerated carriers must have excess energies higher than the band gap itself. In graphene, which is gapless, inverse Auger scattering is instead predicted to be dominant at the earliest time delays. Here, $<8$ femtosecond extreme-ultraviolet pulses are used to detect this imbalance, tracking both the number of excited electrons and their kinetic energy with time- and angle-resolved photoemission spectroscopy. Over a time window of approximately 25 fs after absorption of the pump pulse, we observe an increase in conduction band carrier density and a simultaneous decrease of the average carrier kinetic energy, revealing that relaxation is in fact dominated by inverse Auger scattering. Measurements of carrier scattering at extreme timescales by photoemission will serve as a guide to ultrafast control of electronic properties in solids for PetaHertz electronics., Comment: 16 pages, 8 figures

The dimpling of the CuO_2 planes (spacing between the O2,3 and Cu2 layers) in YBa_2Cu_3O_x has been measured as a function of oxygen concentration and temperature by yttrium x-ray extended-fine-structure spectroscopy (EXAFS). The relative variations of the dimpling with doping (x=6.806-6.984) and temperature (20-300 K) are weak (within 0.05 AA), and arise mainly from displacements of the Cu2 atoms off the O2,3 plane towards Ba. The dimpling appears to be connected with the transition from the underdoped to the overdoped regimes at x=6.95, and with a characteristic temperature in the normal state, T*=150 K., Comment: 6 pages, 2 ps figs, LaTEX, Elsevier Elsart style