Quantum Transport and Cyclotron Resonance Study of Ge/SiGe Quantum Wells in High Magnetic Fields

Shubnikov-de Haas oscillation and cyclotron resonance were studied for high mobility p-type Ge channels in strained Ge/Si_1?x Ge _x quantum wells, using pulsed high magnetic fields up to 50 T. Fine quantum oscillations were observed in ρ _xx . Reflecting the complex Landau level structure in the nearly degenerate valence bands, the Fourier transform of the oscillatory spectra consists of several peaks. Cyclotron resonance was measured at photon energies between 10 and 17 meV. Two well-defined resonance peaks were observed in two samples with different x, resulting in different strains. A large non-parabolicity and large strain dependence of the effective masses were observed.     

Anomalies in the Galvanomagnetic Properties of Fe1.9V1.1Al Pseudogap Semiconductors at High Magnetic Fields

The high-field dependence of the galvanomagnetic properties of Fe_1.9 V_1.1Al compounds was measured in the temperature range from 2.5 to 100 K and in magnetic fields of up to 15 T. We observe that the Hall coefficient decreases with magnetic field, increasingly at low temperatures (2.5–15 K). The magnetoresistivity is negative, but no saturation occurs at fields of up to 15 T. The observed peculiarities of the galvanomagnetic properties can be explained theoretically and confirm that Fe_1.9V_1.1Al compounds show a pseudogap semiconductor behavior.     

The Influence of the Morphology on the Magnetic Properties of Poly(3-hexylthiophene)

The influence of the morphology on the magnetic properties of poly(3-hexylthiophene) has been studied and the results reported. The changes in the saturation magnetization were explained considering the polymer morphology prepared with different amounts of water in the solution during sample synthesis. The results show that the saturation magnetization is maximized for 200 ppm of the water in acetonitrile solution.     

The Discontinuity in the First Derivative of the ITS-90 at the Triple Point of Water

This paper investigates the discontinuity in the derivative [dW/dT ₉₀]_TPW of the ITS-90 at the triple point of water, using data for over 40 calibrated standard platinum resistance thermometers (SPRTs). It finds that the discontinuity is in most cases somewhere between 0 and ?6 parts in 10⁵, in relative terms, but that the higher numerical values are obtained for ‘less ideal’ SPRTs (those with lower temperature coefficients of resistance), and also for sub-ranges not extending beyond the indium point. These results are investigated vis-à-vis the long-standing observation that the ITS-90 reference values W _r(Ga) and W _r(Hg) are not completely consistent with data for W(Ga) and W(Hg) for real SPRTs. It discusses what may be done in a future scale to ensure continuity in the first derivative, and it concludes with a comment about the acceptance criteria for SPRTs in the scale.     

Effect of High Magnetic Fields on the Charge–Density–Wave State in NbSe3

We present a systematic study on a large magnetoresistance in NbSe₃ as a function of temperature under various pressures. The large magnetoresistance below T _c2 is observed as long as the T _c2-CDW phase exists. However, when the T _c2-CDW phase is suppressed totally by high pressure and the superconducting phase is induced at the same time, no anomaly, including the large magnetoresistance, is induced by a magnetic field up to 12 T. The origin of the large magnetoresistance is discussed by considering normal carriers on the ungapped Fermi surface created on the CDW transition and comparing this magnetoresistance with the pressure-induced magnetoresistance that is newly observed above T _c2.     

Magneto-Absorption in the α Phase of Solid Oxygen at Megagauss Magnetic Fields

Optical absorption spectra of solid oxygen α phase and liquid oxygen were measured in high magnetic fields over 100 T using a single turn coil method. The absorption originates from the bimolecular transition was observed. The spectra strongly reflect the local magnetic interaction between two oxygen molecules. The shape of the absorption spectrum of the α oxygen changed dramatically with increasing magnetic fields, even though the absorption intensity of liquid oxygen simply declined. This difference cannot be explained by only the local magnetic interaction, and we speculate that the field induced lattice distortion plays an important role in the solid oxygen α phase.     

Sound Velocity Measurements in the Low and the High Field Phases of the Nuclear-Ordered bcc Solid 3He in Magnetic Fields

We have measured the temperature and magnetic-field dependences of the sound velocity for one longitudinal and two transverse waves in the low field phase (LFP) and the high field phase (HFP) of nuclear spin ordered bcc solid ³He crystals with a single magnetic domain along the melting curve. From sound velocity measurements for various crystal orientations as a function of the sound propagation direction, we determined the elastic stiffness constants, c _ij (T,B). In the LFP with tetragonal symmetry for the nuclear spin structure, we extracted six nuclear spin elastic stiffness constants Δc _ij ^ℓ (T,0.06 T) from the temperature dependence of the sound velocity at 0.06 T and Δc _ij ^ℓ (0.5 mK,B) from the magnetic-field dependence of sound velocity at 0.5 mK. In the HFP with cubic symmetry for the nuclear spin structure, we extracted three Δc _ij ^h (T,0.50 T) at 0.50 T and Δc _ij ^h (0.5 mK,B) at 0.5 mK. At the first-order magnetic phase transition from the LFP to the HFP at the lower critical field B _c1, large jumps in sound velocities were observed for various crystal directions and we extracted three . Using the thermodynamic relation between Δc _ij and the change in the internal energy for the exchange interaction in this system, ΔU _ex(T,B), Δc _ij are related to the generalized second-order Grüneisen constants Γ _ij ^X ≡∂ ²ln X/∂ ε _i ∂ ε _j as Δc _ij (T,B)=Γ _ij ^X ΔU _ex(T,B), where X represents some physical quantity which depends on the molar volume and ε _j is the j-th component of a strain tensor. In the LFP, the Δc _ij ^ℓ (T,0.06 T) were proportional to T ⁴, and Δc _ij ^ℓ (0.5 mK,B) were proportional to B ². We extracted for the spin wave velocity in the LFP, s ^ℓ , from Δc _ij ^ℓ (T,0.06 T) and for the inverse susceptibility, 1/χ ^ℓ from Δc _ij ^ℓ (0.5 mK,B). In the HFP, Δc _ij ^h (T,0.50 T) were proportional to T ⁴ and Δc _ij ^h (0.5 mK,ΔB) were proportional to ΔB(≡B−B _c1). We obtained for the spin wave velocity in the HFP, s ^h , from Δc _ij ^h (T,0.50 T) and for B _c1 from Δc _ij ^h (0.5 mK,ΔB). The values obtained for and were compared with the Multiple Spin Exchange model (MSE) with three parameters by using analytic expressions for s ^ℓ and χ ^ℓ . The three-parameter MSE does not agree with the observed Δc _ij in the LFP.      

The Influence of the Interface on the Magnetic State in Two-Layer Films of the Fe–Bi System

Technical Physics Letters - Results of the experimental investigation of two-layer films in the Fe–Bi system are presented. It is found that the order of sequential deposition of the magnetic...     

Development of the High-Field Imaging System in Pulsed-High Magnetic Fields and Its Application to Manganites

We developed a high-speed polarizing microscope imaging system combined with a 37 T pulse magnet. With utilizing this system, we can visualize some kinds of structural transitions induced by high magnetic fields. The efficiency of this system was tested through observation of the field-induced collapse of charge-orbital ordering (COO) in mixed-valent manganites. In perovskite-type Nd_1/2Sr_1/2MnO₃, quantitative analyses of the obtained polarizing microscope images clearly show the discontinuous change in birefringence accompanied with hysteresis, which are characteristic of the first order transitions. This observation of field-induced melting of the COO was also successful in a layered manganite La_1/2Sr_3/2MnO₄ in which changes in magnetization and magnetoresistance at the transition are less clear. The present success in observation of the melting of the COO demonstrates the potential applicability of this system to visualize other kind of structural transitions even in a tiny piece of crystal.     

Magnetotransport in the CeIrIn5 System: The Influence of Antiferromagnetic Fluctuations

We present an overview of magnetotransport measurements on the heavy-fermion superconductor CeIrIn₅. Sensitive measurements of the Hall effect and magnetoresistance are used to elucidate the low-temperature phase diagram of this system. The normal-state magnetotransport is highly anomalous, and experimental signatures of a pseudogap-like precursor state to superconductivity, as well as evidence for two distinct scattering times governing the Hall effect and the MR, are observed. Our observations point out the influence of antiferromagnetic fluctuations on the magnetotransport in this class of materials. The implications of these findings, both in the context of unconventional superconductivity in heavy-fermion systems and in relation to the high-temperature superconducting cuprates, are discussed.     

Observation of the Semiconductor-Semimetal and Semimetal-Semiconductor Transitions in Bi Quantum Wires Induced by Anisotropic Deformation and Magnetic Field

The semimetal-semiconductor transition is observed in glass-coated quantum single-crystal bismuth wires with diameters less than 70 nm due to the quantum size effect. It is found that elastic deformation of Bi nanowires (10 $\bar{1}$ 1) oriented along the wire axis with the semiconductor dependence R(T) leads to the approaching of L and T bands and to the semiconductor-semimetal transition; as a result, Shubnikov-de Haas oscillations appear on the magnetoresistance dependences R(H). It is shown that strong magnetic field and elastic deformation are the tools to control gap size in quantum bismuth wires, which is principal for their practical use in particular in thermoelectricity.     

The Influence of Lactose Pseudopolymorphic Form on Salbutamol Sulfate–Lactose Interactions in DPI Formulations

A series of 63- to 90-μm sieve-fractioned lactose pseudopolymorphs were investigated in terms of carrier functionality for dry powder inhaler (DPI) formulations. Stable α-anhydrous, α-monohydrate, and β-anhydrous were chosen as model pseudopolymorphs. In addition, the β-anhydrous was further purified to remove residual α-monohydrate content (β-treated). The carriers were investigated in terms of morphology, particle size, crystallinity, and surface energy using inverse gas chromatography. Furthermore, the lactose samples carrier performance was evaluated by studying the aerosolization efficiency of the model drug, micronized salbutamol sulfate, from drug–carrier blends using a next generation impactor (NGI). In general, the aerosol performance of drug from carrier followed the rank order α-monohydrate?>?β-anhydrous?>?β-treated?>?α-anhydrous. Significant difference in carrier size was observed, specifically with relation to the amount of fines (where a rank order of β-treated?>?β-anhydrous?>?α-monohydrate?>?α-anhydrous. No direct relationship between fine content and particle morphology was observed. In comparison, an inverse relationship between surface energy and aerosolization efficiency was found, where a plot of fine particle fraction (aerodynamic diameter < 4.46?μm) against total surface energy resulted in R²?=?.977. Such observations are most likely due to increased particle carrier adhesion and reduced drug liberation during the aerosolization process, indicating surface chemistry (in this case due to the existence of different pseudopolymorphs) to play a dominating role in DPI systems.     

Electrical Conductivity of Thin Polycrystalline La0.83Sr0.17MnO3 Films in Pulsed High Electric and Magnetic Fields

The electrical conductivity of thin polycrystalline La_0.83Sr_0.17MnO₃ films was investigated. These films were simultaneously affected by a single electrical pulse having a pulse length of several ns and a half-sinus magnetic pulse with a pulse length of 1 ms and amplitude ranging up to 20 T. The influence of the high magnetic field on the electroresistance was studied at electric field strengths up to 80 kV/cm when the temperature of the film ranged from 100 K to 300 K. It was found that depending on the temperature and magnetic field value the electroresistance (ER) can be enhanced or suppressed by the applied magnetic field. These results are explained by assuming that the ER appears due to inelastic multistep tunneling through grain boundaries and by taking into account the redistribution of voltage across crystalline grains and grain boundary regions.     

Effect of a High Magnetic Field on the Shape of the γ' Precipitates in Cast Nickel-based Superalloy K52

The shape change of the γ' precipitates of cast Ni-based superalloy K52 after aging treatment under a high magnetic field was investigated.The results show that duplex γ' precipitates are present in the γ matrix after aging treatment with or without the magnetic field.One is the coarse particles with average size of 500 nm; the other is fine spherical γ' precipitates with average of 100 nm in diameter.The application of a 10T magnetic field only results in the shape of the coarse γ' particles changing from spherical to cuboidal when the alloys subjected to the same heat treatments.This shape change was mainly discussed based on the strain energy increase caused by the difference in magnetostriction between the γ matrix and γ' precipitates.The fine γ'particles still keep spherical.Further TEM observations shows that a number of γ particles in nano-scale precipitate in the coarse γ' particles in the specimens treated without the magnetic field.In addition, it was found that the magnetic field caused the decrease of the hardness in the alloy, and the hardness was associated with the field direction.     

Experimental Studies of the Influence of a High‐Frequency Electromagnetic Field on the Convection of Fluids in a Vertical Tube

Results of experimental studies of the influence of a highfrequency electromagnetic field on a change in the levels of fluids in a vertical tube are reported.     

Upper Critical Field Measurements up to 60 T in Arsenic-Deficient LaO0.9F0.1FeAs1−δ : Pauli Limiting Behavior at High Fields vs. Improved Superconductivity at Low Fields

We report resistivity and upper critical field B _c2(T) data for As-deficient LaO_0.9F_0.1FeAs_1?δ in a wide temperature and field range up to 60 T. These disordered samples exhibit a slightly enhanced superconducting transition at T _c =29 K and a significantly enlarged slope dB _c2/dT=?5.4 T/K near T _c which contrasts with a flattening of B _c2(T) starting near 23 K above 30 T. This flattening is interpreted as Pauli limiting behavior (PLB) with B _c2(0)≈63 T. We compare our results with B _c2(T)-data reported in the literature for clean and disordered samples. Whereas clean samples show no PLB for fields below 60 to 70 T, the hitherto unexplained flattening of B _c2(T) for applied fields H ∥ ab observed for several disordered closely related systems is interpreted also as a manifestation of PLB. Consequences of our results are discussed in terms of disorder effects within the frame of conventional and unconventional superconductivity.     

The effect of residual stresses in the ZnO buffer layer on the density of a ZnO nanowire array

Density control is a valuable concern in the research of ZnO nanowire arrays. In this study, unannealed and annealed ZnO thin films were used as substrates to fabricate ZnO nanowire arrays. In the unannealed thin film, an inhomogeneous distribution of the nanowire array was found: the density of nanowires decreases with the increase of distance to the edge. In the annealed thin film, the density of nanowire array becomes larger and more homogeneous. Moreover, nanowires are found in high density along microcracks. It is proposed that the residual stresses in the thin film and the density of the nanowire array are in inverse proportion, leading to the results mentioned above. The relationship between residual stresses and the density of nanowires will have potential applications in modifying the density of ZnO nanowire arrays.