Renormalization of Competing Interactions and Superconductivity on Small Scales

The interaction-induced orbital magnetic response of a nanoscale ring is evaluated for a diffusive system which is a superconductor in the bulk. The interplay of the renormalized Coulomb and Fröhlich interactions is crucial. The magnetic susceptibility which results from the fluctuations of the uniform superconducting order parameter is diamagnetic (paramagnetic) when the renormalized combined interaction is attractive (repulsive). Above the transition temperature of the bulk the total magnetic susceptibility has contributions from many wave-vector- and (Matsubara) frequency-dependent order parameter fluctuations. Each of these contributions results from a different renormalization of the relevant coupling energy, when one integrates out the fermionic degrees of freedom. The total diamagnetic response of the large superconductor may become paramagnetic when the system’s size decreases.     

Photoluminescence and photoinduced magnetic phase transition in an organic radical TTTA crystal studied by two-photon absorption

Photoluminescence as well as photoinduced diamagnetic to paramagnetic phase transition in a strongly correlated electron system, an organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystal, was investigated under two-photon excitation with different photon densities. Below the threshold photon density to drive the photoinduced phase transition (PIPT), the diamagnetic phase shows a broad luminescence band with a large Stokes shift, whose intensity obeys almost second power law of the excitation photon density. Above the threshold photon density, on the other hand, the diamagnetic to paramagnetic phase transition effectively takes place with a large conversion yield and a steep response instead of an occurrence of the photoluminescence, indicating that the phase transition is optically induced by two-photon absorption. As far as we know, this is the first observation of the PIPT phenomena mediated by two-photon absorption.     

磁光材料Verdet常数贡献性的讨论

Verdet常数是表征材料磁光性能的重要参数,具有波长和温度依赖性.为了更好地分析入射光波长、温度等对Verdet常数的影响机理,从基础理论切入,分析了现有理论的优缺点.结合光的波粒二象性特性,提出了波动跃迁性贡献理论,即法拉第效应是光的波动性作用以及电偶极跃迁作用带来的贡献之和,波动性对偏转角的贡献为正,跃迁性贡献为负.在抗磁性材料中,波动性贡献大于跃迁性贡献,Verdet常数为正;顺磁性材料中,跃迁性贡献远大于波动性贡献,Verdet常数为负.进而分别以典型抗磁性材料重火石玻璃ZF1和顺磁性材料铽镓石榴石为例,并结合相关数据、参数、模型,对理论进行了验证.试验结果表明,在精确描述材料Verdet常数方面,波动跃迁性贡献理论具有一定的优越性.     

Spin and orbital quantization of electronic states as origins of second harmonic generation in semiconductors

Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, induced by an external magnetic field H, have been identified experimentally by studying the diluted magnetic semiconductor (Cd,Mn)Te. For paramagnetic (Cd,Mn)Te the SHG response is governed by spin quantization of electronic states, in contrast with diamagnetic CdTe with its dominating orbital quantization. The mechanisms can be identified by the distinct magnetic field dependence of the SHG intensity which scales with the spin splitting in the paramagnetic case as compared to the H2 dependence observed for the diamagnetic case.     

Magnetic properties of multiwalled carbon nanotubes as a function of acid treatment

We investigate the electronic properties of multiwalled carbon nanotubes both before and after acid treatment with concentrated sulphuric and nitric acids. Magnetic susceptibility measurements were performed using a SQUID magnetometer and show that there is a considerable enhancement in the density of states at the Fermi level. The data shows that the diamagnetic influence from the graphitic nanotubes dominates. We experimentally observe, after acid treatment, that the diamagnetic susceptibility remains unchanged at 5 K but notably decreases at 77 K. We propose the acid treatment has increased the Van Vleck paramagnetic contribution lowering the diamagnetic response from the π-electron orbital magnetisation. The Van Vleck paramagnetic contribution is finite-temperature dependent with a diminishing contribution at higher fields.     

Influence of surface electronic structure on the Casimir force

Recent nonlocal microscopic theory of Casimir force which expresses the interaction energy between two metallic slabs in terms of surface polariton propagators calculated from diamagnetic and paramagnetic current-current response functions, sensitive to details of the surface electron density profiles and single-particle excitations on the surfaces, is used here to calculate various contributions to the Casimir energies for a silver film described by two different models. Current-current response functions are constructed from energy levels and wave functions obtained in two different models: jellium and Chulkov one-dimensional model potential, and the results are compared with the local plasmon model results. The results show how the details of such surface electronic structure modify Casimir force.     

Diamagnetic enhancement in amorphous semiconductors

We analyse the diamagnetic susceptibility χ of a model two-dimensional semiconductor both in crystalline and amorphous phases using a linear combination of hybrids model. We show that the large diamagnetic enhancement in amorphous Si and Ge is due to the reduction of the Van Vleck type paramagnetic term.     

A simple route to the energy shift between an electrically polarizable molecule and a magnetically susceptible molecule via the electromagnetic energy density

The van der Waals dispersion interaction between a molecule that is electrically polarizable and one that is magnetically susceptible, is recalculated within the framework of non-relativistic quantum electrodynamics. The energy shift is obtained in a simple way by calculating the response of a test polarizable body to the electromagnetic energy density due to a second source molecule. It is confirmed that the near-zone asymptote of the potential between an electric dipole polarizable molecule and a paramagnetic one varies as R ^{? 4}. Inclusion of the often neglected diamagnetic coupling term, however, results in an R ^?5 dependent short-range behaviour, which is seen to dominate over the paramagnetic contribution in the near-zone. For larger intermolecular distances, the expected R ^?7 dependence on separation is found for both paramagnetic and diamagnetic susceptible molecules interacting with an electric dipole polarizable one.     

Magnetic circular dichroism in the luminescence of F-centres in KI

Magnetic field induced circular polarization of the F-centre emission has been measured in KI at 1.9 K in fields up to 80 kG. Both the diamagnetic (field dependent) and the paramagnetic contributions (dependent upon the spin polarization of the relaxed excited state) have been detected. The spin polarization is produced by a pump beam modulated between left and right circular polarization. The expected behaviour of the spin polarization as a function of the frequency of the modulation has been observed. Knowledge of these small dichroic effects gives further insights into the nature of the relaxed excited state.     

51V nuclear magnetic resonance study of vanadium oxide nanotubes

We report on a ⁵¹VNMR study of vanadium oxide - decylamine nanotubes. ⁵¹V NMR spectra show three lines resulting from a diamagnetic V^5?+? and two paramagnetic V^4?+? ions, respectively. The V^4?+?/V^5?+? ratio is estimated to be ~0.47. ⁵¹V spin-lattice relaxation comprises both magnetic and quadrupolar contributions.     

Third-Order Magnetic Susceptibility of an Ideal Fermi Gas

At low temperature and under weak magnetic field, non-interacting Fermi gases reveal both Pauli paramagnetism and Landau diamagnetism, and the magnitude of the diamagnetic susceptibility is 1/3 of that of the paramagnetic one. When the temperature is finite and the magnetic field is also finite, we demonstrate that the paramagnetism and diamagnetism start to deviate from the ratio 1/3. For understanding the magnetic properties of an ideal Fermi gas at quite low temperature and under quite weak magnetic field, we work out explicitly the third-order magnetic susceptibility in three cases, from intrinsic spin, orbital motion and in total. An interesting property is in third-order magnetic susceptibilities:when viewing individually, they are both diamagnetic, but in total it is paramagnetic.     

Symmetry breaking effect on persistent current in graphene rings

We calculate the electronic structure and persistent current of graphene rings based on tight binding theory. The sixfold rotational symmetrical graphene rings exhibit diamagnetic response with carriers flowing anticlockwise along the rings. When symmetry is broken by defect, these rings remain diamagnetic response. While for asymmetrical graphene ring with the same size, the typical current is several orders of magnitude smaller than that of sixfold rotational symmetrical graphene ring. Especially, the asymmetrical graphene rings exhibit not only diamagnetic but also paramagnetic response.     

Calculation of proton N.M.R. chemical shifts by means of a finite perturbation method

The magnetic shielding effect due to neighbouring carbon atoms through the diamagnetic and paramagnetic terms is calculated by means of a finite perturbation method in cooperation with a semi-empirical INDO molecular orbital method. The behaviour of the components of the shielding tensor arising from 2s and 2p orbitals centred on a neighbouring carbon is shown as a function of the distance, R, between the proton considered and the carbon. It is pointed out that the treatment by Pople and McConnell in the calculation of the proton chemical shift must be used carefully in unsaturated hydrocarbons, because some of the contributions from a neighbouring carbon do not show an R ^-3 dependence but an R ^-2 dependence. It is also shown that the gross trend of the observed proton chemical shifts in hydrocarbons is reproduced fairly well in the present calculation.     

Muon spin-lattice relaxation and muonium diffusion in ice

Longitudinal muon spin relaxation is measured in ice, using samples with and without enrichment in H₂ ¹⁷O, with a view to studying the mobility of the muonium fraction. A conventional analysis of the data, on the assumption that relaxation of the diamagnetic fraction is negligible, suggests that more than one mechanism of muonium relaxation is at work. A Bayesian analysis warns that separation of the diamagnetic and paramagnetic signals may not be so straightforward.     

Thermoluminescence and Magnetic Properties of irradiated Sodium Chloride

The diamagnetic susceptibility of sodium chloride crystal decreases on irradiation with x-rays andγ-rays. This is due to the induced paramagnetic centres in the crystal. The difference in diamagnetic susceptibility of the crystal before and after irradiation obeys Curie Law. On thermal bleaching the diamagnetic susceptibility recovers its original value. The changes in magnetic susceptibilities which occur at different stages of thermal bleaching are found to have correspondence with the integrated intensity of thermoluminescence. It is concluded that the destruction of F-Centres alone can not account for the intensity of thermoluminescence or changes in magnetic property.     

Oscillatory magnetization of two-dimensional electron gas

Diamagnetic moment of the two-dimensional electron gas is calculated for finite temperature using a simple energy band model and assuming no collisional broadening of Landau levels. Numerical results are presented for GaAs band parameters. The diamagnetic moment oscillates around zero value as a function of magnetic field strength and tends to zero at low fields. It is concluded that both the diamagnetic and the paramagnetic susceptibilities of the 2D electron gas vanish in the low field limit.     

Depolarized Light Scattering from Paramagnetic Liquids in a Magnetic Field

In order to identify spectral features and molecular movement types the magnetic field's influence on rotational and diffuse shear modes of paramagnetic liquids is analysed. Consideration of the corresponding changes in depolarized (VH) light scattering spectra illustrates a systematic method of studying both paramagnetic and diamagnetic liquids.     

Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite

In this work we report that when ferromagnetic metals (Fe,Co and Ni) are thermally evaporated onto n-layer graphenes and graphite,a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure.Similar features can also be observed for paramagnetic metals,such as Mn,Al and Pd.Meanwhile,metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals (Au and Ag).An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal;and the morphologies of diamagnetic metal do not change after the application of an external magnetic field.We discuss the possible reasons for these novel and interesting results,which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.     

The Faraday effect in Y3Fe5−xGaxO12 garnet

The effects of replacing Fe by Ga is to cause conversion from paramagnetic rotation to diamagnetic.We are indebted to A. A. Shvarts for a discussion of then results.