Resonant peak splitting through magnetic Kronig–Penney superlattices in graphene

The resonance splitting effect of Dirac electrons through magnetic Kronig–Penney superlattices with delta-function barriers in graphene is studied theoretically. It is found that both transmission probability and conductance present (n−1)-fold$(n-1)\mathrm{-}\mathrm{fold}$ resonant peak splitting in n vector potential barriers, which is the same as that of standard electrons in semiconductor superlattices [R. Tsu, L. Esaki, Appl. Phys. Lett. 22 (1973) 562]. The resonant peak splitting and wave-vector filtering could be controlled by adjusting the transverse wave vector and structural parameters. These properties may be useful for the design of graphene-based electronic devices.     

Interlayer-exciton mediated three-hole-Auger-decay in the π⁎-band of highly oriented pyrolytic graphite

Resonant photoemission spectroscopy (resPES) is used to probe the occupied π- and unoccupied π^⁎-bands of carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is studied at the C1s edge. We find strong resonant features at 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (45°) only in the σ^⁎-region. In the π^⁎-region, however, it proceeds under 67.5° in terms of a E_bind(ħω) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model. We discuss the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to identify interlayer–substrate interaction of the carbon layers involved.     

Modification of induced spin-orbit splitting of the π states of graphene during the joint intercalation of Bi and noble metals

The effect of intercalation of Bi atoms and the joint intercalation of atoms of Bi and noble metals (Au, Cu) on the spin and electron structure of graphene formed on Ni(111) is investigated by angle and spin-resolved PES. It is shown that the spin-orbit splitting of π states of graphene of 20–30 meV is observed for the joint intercalation of Bi and Au.     

π-phase magnetism in ferromagnet-superconductor superlattices

New 0π and ππ Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) states with antiferromagnetic orientation of magnetizations in the neighboring layers of a ferromagnetic metal (FM) are predicted for FM/superconductor (FM/S) superlattices. Under certain conditions, the critical temperature T _c of these states is higher than for the known 00 and π0 LOFF states with ferromagnetic ordering of the FM layers. It is shown that the nonmonotonic behavior of T _c in the FM/S superlattices with S-layer thickness d _s less than the threshold value d _s ^π is due to the phase transition cascade 0π-ππ-0π At d _s >d _s ^π , the T _c oscillations are caused by the 00-π0-00 transitions. New logic elements based on the FM/S structures and combining the advantages of the superconducting and magnetic data-record channels in a single sample are proposed.     

Signature splitting of the πh11/2 band and high-spin structures in 155Tb

Seven experimentally observed bands of 155Tb are analyzed in detail, using the particle-number-conserving method for treating the cranked shell model with monopole and quadrupole pairing interactions. We satisfactorily reproduce the experimental alignments and especially focus on the microscopic mechanism of the second back-bending and the influence of pair interaction on ultrahigh spins. Our calculated results show that the πi13/2 orbitals are too high to give a contribution to the moment of inertia below hω≈0.7 MeV. Instead, the crossing between the π[541]l/2 and other proton orbitals is responsible for the second back-bending. We assign a possible configuration to the decoupled band found in 155Tb and predict eleven bands which are experimentally unobserved.     

Hypernuclear production induced by in-flight K and π

The development in treating K- and -induced hypernuclear production reactions is reviewed, including the application of DWIA to the (K^–, K⁺) reaction to produce ^–. After summarizing the conventional DWIA treatment without spin-dependence, we discuss the calculational method of strength functions up to the continuum. Finally the process is reformulated starting from the elementary amplitudes with the spin-flip component as well as the spin-nonflip one. The new treatment is shown to be powerful and the emphasis is put on the production of polarized hypernuclei, which provides a useful spectroscopic tool for the weak-decay mechanism.Dedicated to our distinguished collaborator, Professor Jan ofka (1943–1991), to the memory of his inspiration in hypernuclear physics and his wide, friendly activities in our community.The authors are very grateful to the late Professor Jan ofka who was a distinguished collaborator for a long time. He coordinated many collaborations between e and Japan. We will miss his scientific and organizational activities in hypernuclear physics. The authors express their thanks to O. Richter, M. Sotona, R. Wünsch, H. Ejiri and T. Kishimoto for collaboration and discussion on several parts of the calculated results. This work has been supported by the Grant-in-Aid for Scientific Research (C) and also by A Grant under The Monbusho International Scientific Research program (Joint Research 1990–1991).     

Rydberg electromagnetically induced transparency and Autler–Townes splitting in a weak radio-frequency electric field

We utilize an electromagnetically induced transparency(EIT) of a three-level cascade system involving Rydberg state in a room-temperature cell, formed with a cesium 6 S_(1/2)–6 P_(3/2)–66 S_(1/2) scheme, to investigate the Autler–Townes(AT)splitting resulting from a 15.21-GHz radio-frequency(RF) field that couples the |66 S_(1/2) → |65 P_(1/2) Rydberg transition.The radio-frequency electric field induced AT splitting, γAT, is defined as the peak-to-peak distance of an EIT-AT spectrum.The dependence of AT splitting γAT on the probe and coupling Rabi frequency, ?_p and ?_c, is investigated. It is found that the EIT-AT splitting strongly depends on the EIT linewidth that is related to the probe and coupling Rabi frequency in a weak RF-field regime. Using a narrow linewidth EIT spectrum would decrease the uncertainty of the RF field measurements.This work provides new experimental evidence for the theoretical framework in [J. Appl. Phys. 121, 233106(2017)].     

σ and π-band dispersion of graphite from polarized resonant inelastic X-ray scattering measurements

Resonant inelastic X-ray scattering of highly oriented pyrolytic graphite (HOPG) is observed above the C 1s threshold at different polarization angles. It is shown that combining the polarization and excitation energy dependence of X-ray emission spectra makes it possible to perform quantitative band mapping selective to the chemical bonding (σ and π).     

Spin-orbit splitting in σ-hypernuclei

The shell model analysis of experimental 0⁺, 2⁺ spectra of and as obtained from (K ^–, ⁺) in-flight and stoppedK ^– reactions, is performed. It suggests a large (twice that for nucleons) spin-orbit splitting of hyperon levelsp _3/2 andp _1/2. Certain constraints on effective central N interaction arise, as well. Some experiments are put forward to further test this value and to extend it to hypernuclei.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Magnetic field induced phase branches of the superconducting transition in two-dimensional square π-loop arrays

Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional （2D） square π-loop arrays given by Li et al [2007 Chin. Phys. 16 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li＇s paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux φe through each loop and monotonically on the screen parameter β of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the π-loop arrays is also discussed.     

Magnetic field induced phase branches of the superconducting transition in two-dimensional square π-loop arrays

Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square $\pi $-loop arrays given by Li \textit{et al} [2007 {\em Chin. Phys.} {\bf 16} 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux $\phi_{\e}$ through each loop and monotonically on the screen parameter $\beta $ of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the $\pi $-loop arrays is also discussed.     

Crystallization of polymer chains induced by graphene： Molecular dynamics study

The present work is devoted to a study of the molecular mechanisms of the crystallization of polymer chains induced by graphene by using molecular dynamics （MD） simulations. From the atomic configuration translation, the number distri- bution of the atoms, and the order parameter S, the crystallization process can be summarized in two steps, the adsorption and the orientation. By analyzing the diffusion properties of the polymer chains, we find that a graphene substrate has a great adsorption for the polymer molecules and the polymer molecules need more time to adjust their configurations. Therefore, the adsorption step and the orientation step are highly cooperative.     

Crossover between electromagnetically induced transparency and Autler–Townes splitting with dispersion

Based on Akaike's information criterion(AIC) for a coherently driven ensemble of cold rubidium atoms, we study the crossover between electromagnetically induced transparency(EIT) and Autler–Townes(AT) splitting from the dispersion as well as the absorption viewpoint. We find that the dispersion signal is more sensitive than the absorption signal, showing more pronounced features in the Akaike per-point weights spectrum, which provides a cleaner way of discerning EIT from AT splitting.     

Broadening processes in GaAsδ-doped quantum wire superlattices

We use both Quantum Hall and Shubnikov de Haas experiments at high magnetic field and low temperature to analyse broadening processes of Landau levels in a δ -doped 2D quantum well superlattice and a 1D quantum wire superlattice generated from the first one by controlled dislocation slips. We deduce first the origin of the broadening from the damping factor in the Shubnikov de Haas curves in various configurations of the magnetic field and the measured current for both kinds of superlattice. Then, we write a general formula for the resistivity in the Quantum Hall effect introducing a dephasing factor we link to the process of localization.     

Dynamic dc voltage band in vertical transport of superlattices

By the numerical method, we show a transition process from static to dynamic electric-field domain formation in semiconductor superlattices. During this transition, there can be noticed a sawtooth-like zone in which static and dynamic electric-field domain zones appear alternatively with increasing voltage. Therefore, a dynamic dc voltage band emerges from each sawtooth-like branch of the current－voltage characteristic. These results are qualitatively in agreement with experiment.     

Magnetic resonance evidence of manganese–graphene complexes in reduced graphene oxide

We report on EPR and NMR study of reduced graphene oxide (RGO) produced by the Hummers method. We show that this RGO sample reveals isolated Mn²⁺ ions, which originate from potassium permanganate used in the process of the sample preparation. These ions form paramagnetic charge-transfer complexes with the graphene planes and contribute to the ¹³C spin–lattice relaxation.     

Impurities in type-II-staggered InAs/AℓSb superlattices

The physics of impurities in Type-II staggered superlattices is reviewed, with emphasis on changes of doping character, such as shallow to deep and deep to false-valence transitions, that can result from altering layer thicknesses. It is shown how some impurities can change their doping characters from "deep acceptors" (semi-insulating) to shallow donors (n-type) as functions of layer thicknesses in superlattices such as InAs/AℓSb. A particularly important case is an Aℓ_Sb antisite defect in an AℓSb layer of an InAs/AℓSb superlattice. This defect is a deep trap or "deep acceptor" in AℓSb, and a remote donor in some superlattices, depending on the layer thicknesses. It can, by itself, control the electron gas density in a superlattice structure, and so can play an important role in the development of high-speed field-effect transistors.