Optically-pumped stimulated recombination radiation inp-type InSb in high magnetic fields

In this paper measurements of the frequency, linewidth and polarization of stimulated recombination radiation (SRR) fromp-type InSb are reported. The samples had low excess-carrier concentrations between 10¹⁴ and 10¹⁵ per cm³ and different lengths between 0.4 and 9 mm. They were held in magnetic fields up to 6T at temperatures of pumped liquid helium. The excitation was done optically by the radiation of a Q-switched CO-laser. We could observe a number of different stimulated processes:

1. band-to-band recombination (tuning between 1875 and 1980 cm^?1),
2. band-to-acceptor recombination (tuning between 1840 and 1930 cm^?1),
3. stimulated spin-flip Raman scattering (SFR) of the SRR by excited electrons,
4. SFR of the laser by excited electrons and its interaction with the SRR.

From the observed shift of the band gap by exchange and correlation energy the number of created electron-hole pairs can be calculated to be up to 10¹⁶ per cm³. The observed acceptor binding energy varies from 66 cm^?1 atB=0 to 71 cm^?1 at 4.5T.     

Graphene in high magnetic fields

Carbon-based nano-materials, such as graphene and carbon nanotubes, represent a fascinating research area aiming at exploring their remarkable physical and electronic properties. These materials not only constitute a playground for physicists, they are also very promising for practical applications and are envisioned as elementary bricks of the future of the nano-electronics. As for graphene, its potential already lies in the domain of opto-electronics where its unique electronic and optical properties can be fully exploited. Indeed, recent technological advances have demonstrated its effectiveness in the fabrication of solar cells and ultra-fast lasers, as well as touch-screens and sensitive photo-detectors. Although the photo-voltaic technology is now dominated by silicon-based devices, the use of graphene could very well provide higher efficiency. However, before the applied research to take place, one must first demonstrates the operativeness of carbon-based nano-materials, and this is where the fundamental research comes into play. In this context, the use of magnetic field has been proven extremely useful for addressing their fundamental properties as it provides an external and adjustable parameter which drastically modifies their electronic band structure. In order to induce some significant changes, very high magnetic fields are required and can be provided using both DC and pulsed technology, depending of the experimental constraints. In this article, we review some of the challenging experiments on single nano-objects performed in high magnetic and low temperature. We shall mainly focus on the high-field magneto-optical and magneto-transport experiments which provided comprehensive understanding of the peculiar Landau level quantization of the Dirac-type charge carriers in graphene and thin graphite.     

Iron-based superconductors in high magnetic fields

Here we review measurements of the normal and superconducting state properties of iron-based superconductors using high magnetic fields. We discuss the various physical mechanisms that limit superconductivity in high fields, and the information on the superconducting state that can be extracted from the upper critical field, but also how thermal fluctuations affect its determination by resistivity and specific heat measurements. We also discuss measurements of the normal state electronic structure focusing on measurement of quantum oscillations, particularly the de Haas–van Alphen effect. These results have determined very accurately, the topology of the Fermi surface and the quasi-particle masses in a number of different iron-based superconductors, from the 1111, 122 and 111 families.     

Towards a quantitative analysis of magnetic force microscopy data matrices

Fast and efficient software tools previously developed in image processing were adapted to the analysis of raw datasets consisting of multiple stacks of images taken on a sample interacting with a measuring instrument and submitted to the effect of an external parameter. Magnetic force microscopy (MFM), a follow-up of atomic force microscopy (AFM), was selected as a first testbed example. In MFM, a specifically developed ferromagnetic scanning tip probes the stray magnetic field generated from a ferromagnetic specimen. Raw scanning probe images taken on soft patterned magnetic materials and continuous thin films were used, together with synthetic patterns exploited to assess the absolute performance ability of the proposed texture analysis tools. In this case, the parameter affecting the sample-instrument interaction is the applied magnetic field. The application discussed here is just one among the many possible, including, e.g., real-time microscopy images (both optical and electronic) taken during heat treatments, phase transformations and so on. Basically any image exhibiting a texture with a characteristic spatial or angular dependence could be processed by the proposed method. Standard imaging tools such as texture mapping and novel data representation schemes such as texture analysis, feature extraction and classification are discussed. A magnetic texture stability diagram will be presented as an original output of the entropic analysis on MFM datasets.     

Single-dot spectroscopy in high magnetic fields

We report on photoluminescence measurements from a single InAs/GaAs quantum dot in magnetic fields up to 28 T. Mesa-patterned structure has been used to limit the number of investigated dots. Three pairs of Zeeman-split emission lines with the same effective g*-factor and diamagnetic shift have been observed. The attribution of the lines to recombination of a neutral exciton, a biexciton, and a charged exciton is discussed.     

Layered superconductors in high magnetic fields

We investigate the possible occurrance of partially depaired states in superconducting intercalated layered systems. Those states are discussed as a possible explanation of the high critical fields found in some of these materials. It is shown that the Chandrasekhar-Clogston limit does not apply to those states mentioned above and that the maximum field compatible with superconductivity is a sensitive function of the shape of the Fermi surface. Mean free path and spin-orbit effects on the partially depaired state are investigated. An experiment is proposed to decide between the partially depaired state and a large spin-orbit scattering rate as possible explanations for the large critical fields.     

Heavy fermions in high magnetic fields

Heavy fermion materials are prototypical strongly correlated electron systems, where the strong electron–electron interactions lead to a wide range of novel phenomena and emergent phases of matter. Due to the low energy scales, the relative strengths of the Ruderman–Kittel–Kasuya–Yosida(RKKY) and Kondo interactions can often be readily tuned by non-thermal control parameters such as pressure, doping, or applied magnetic fields, which can give rise to quantum criticality and unconventional superconductivity. Here we provide a brief overview of research into heavy fermion materials in high magnetic fields, focussing on three main areas. Firstly we review the use of magnetic fields as a tuning parameter,and in particular the ability to realize different varieties of quantum critical behaviors. We then discuss the properties of heavy fermion superconductors in magnetic fields, where experiments in applied fields can reveal the nature of the order parameter, and induce new novel phenomena. Finally we report recent studies of topological Kondo systems, including topological Kondo insulators and Kondo–Weyl semimetals. Here experiments in magnetic fields can be used to probe the topologically non-trivial Fermi surface, as well as related field-induced phenomena such as the chiral anomaly and topological Hall effect.     

Heavy fermions in high magnetic fields

A qualitative picture of the metamagnetic transition in the Anderson lattice model of heavy fermion Ce compounds is described and a strong coupling spin fluctuation theory of the high field state is presented. The field dependence of the minority spin quasiparticle mass is calculated and the onset of the metamagnetic transition with decreasing field is discussed. The theory of the high field state is extended to include Landau levels and the oscillatory behaviour of the spin self-energy as a function of the inverse applied field is investigated. For the heavy fermion model considered such oscillations of the self-energy lead to significant modifications in the standard theory of the de Haas - van Alphen effect. The possible relevance to anomalous experimental results on CeRu₂Si₂ is discussed.     

强磁场下的科学研究

文章介绍了强磁场在半导体物理、低维物理、高温超导体、重费米子、磁学、原子分子物理、化学、有机化合物、材料科学、微重力、核磁共振等领域中的重要作用.     

强磁场下的科学研究

文章介绍了强磁场在半导体物理、低维物理、高温超导体、重费米子、磁学、原子分子物理、化学、有机化合物、材料科学、微重力、核磁共振等领域中的重要作用.     

Resonance THz spectroscopy in high magnetic fields

The employment of the high-magnetic-field resonance spectroscopy to probe magnetic excitations in the THz frequency range is reported. To illustrate the great potential of this technique in solid state physics, we present results of recent electron spin resonance studies of the quantum-tunneling effect in the single-molecule magnet Mn12tba and of the soliton–magnon crossover in Cu-PM, a spin-1/2 Heisenberg chain system with a staggered transverse field. Among others, we report on the successful use of the THz-range time-domain and free electron laser spectroscopy to study magnetic excitation spectra in pulsed magnetic fields.     

Noninteracting electron gas in high magnetic fields

A closed-form expression is obtained for a free electron gas in a magnetic field. The resulting formulation is valid for fields less than 10⁸ gauss and temperatures where de Haas-Van Alphen effects can be neglected.     

Semiconductor quantum dots in high magnetic fields

We review and extend the composite fermion theory for semiconductor quantum dots in high magnetic fields. The mean-field model of composite fermions is unsatisfactory for the qualitative physics at high angular momenta. Extensive numerical calculations demonstrate that the microscopic CF theory, which incorporates interactions between composite fermions, provides an excellent qualitative and quantitative account of the quantum dot ground state down to the largest angular momenta studied, and allows systematic improvements by inclusion of mixing between composite fermion Landau levels (called Λ levels).     

强磁场下锗电阻温度传感器的磁致电阻效应研究

以锗温度传感器GR-1400-AA为研究对象,研究了其在0～16 T磁场下、2～100K温区内的磁致电阻效应。结果表明:在2～20K温区,GR-1400-AA磁效应随温度的升高急剧降低,且场强越高磁效应的变化率越大;在20～100K温区,磁效应随温度的升高趋于平缓;GR-1400-AA磁效应随场强的升高而升高,且温度越低,磁效应的变化率越高,2.1K、16T处的磁效应为2120.3%;GR-1400-AA由磁阻引起的测量温差随温度的升高而升高,随场强的增大而增大,且全为负温差,在6K、2T处和16T、100K处的测量温差分别为-0.24K、-60.4K。不推荐应用在磁场环境下。     

Behavior of dirty superconductors in high magnetic fields

This paper discusses some properties of homogeneous, dirty superconductors, where the motion of electrons in the normal state can be described as a diffusion process. It is shown that at the nucleation field (H _e2 orH _e3) corresponding to the onset of superconductivity, the order parameterΔ(r) satisfies a linearised equation which has the Landau-Ginsburg form atall temperatures. This considerably extends the validity of the existing calculations ofH _e2 andH _e3; it is possible to show in particular that the ratioH _e3/H _e2 and the form of the angular dependence ofH _e3 are independent of temperature. It is also possible to compute explicitely the local density of statesN(r,ω), at any pointr and energyω, for fields slightly belowH _e2 (orH _e3), when the order parameter is stronglyr-dependent. Due to some remarkable sum rule propertiesN (r,ω) depends only on the local value of the order parameterΔ(r). These results may be of use in the interpretation of tunneling experiments on the mixed state and on surface superconductivity.