The melting pressure and entropy of spin ordered solid 3He

We report measurements of the melting pressure of solid ³He between 0.36 mK and 1.2 mK. At 1.030 ± .005 mK we observe a first order phase transition in the solid with a loss in entropy of 0.443R ln². Below ～0.6 mK the melting pressure varies as T⁴, in agreement with antiferromagnetic spin wave theory.     

Redistribution of electrons between ellipsoids in a magnetic field in the quantum limit range in n-Bi-Sb alloys

The magnetoresistivities ρ₂₂(H) and ρ₃₂(H) and the Hall coefficient R _32.1 for single-crystal samples of the n-Bi_0.93Sb_0.07 semiconducting alloy have been measured at low temperatures in magnetic fields up to H=14 T at H∥C ₂. The samples with three electron concentrations n ₁=1.25 × 10¹⁶ cm^s-3, n ₂=3.5×10¹⁶ cm^s-3, and n ₃=1.6×10¹⁷ cm^s-3 have been studied. The strong anisotropy of the electron spectrum of the alloys has made it possible to observe quantum oscillations of the magnetoresistivity ρ₂₂ (H) at H∥C ₂ for electrons of the secondary ellipsoids with the transition to the quantum limit in high magnetic fields. However, in the same magnetic fields, the quantization condition for electrons of the main ellipsoid is not satisfied. An increase in the energy of electrons of the secondary ellipsoids in the magnetic fields of the quantum limit leads to their migration to the main ellipsoid. After the complete migration, the Fermi energy for the alloy samples with the electron concentrations n ₁, n ₂, and n ₃ increases from 7.0 to 11.3 meV, from 11.0 to 17.1 meV, and from 20.2 to 30.6 meV, respectively. After the migration, the magnetoresistivity for electrons of the main ellipsoid increases with an increase in the magnetic field and the specific features in the behavior of the kinetic coefficients are observed in the vicinity of the magnetic field H=10 T. Therefore, the electronic topological transition from the three-valley electron spectrum to the single-valley electron spectrum occurs in the Bi_0.93Sb_0.07 single crystals for H∥C ₂ at low temperatures in the range of magnetic fields of the quantum limit.     

Interaction of transverse magnetoresistance effects in extrinsic and intrinsic InSb

In extrinsic and intrinsic n-InSb the dependence of the resistivity on transverse magnetic fields is investigated. Four contributions are distinguished: the geometrical, the inhomogeneity, the mobility, and the ambipolar effect. The interactions of these effects are studied, not only from the resistivity, but also from the dependence of the electric field in the middle section of rectangular samples on the magnetic field. All theoretical derivations are verified by own experiments and compared to measurements reported in the literature.The interaction of the various magnetoresistance effects is here discussed for the first time, and new assertions on the physical magnetoresistivity, i.e. on the dependence of the carrier mobilities μ^± on the transverse magnetic field B can be made. For electrons μ^? = μ₀^?/(1 + γ^?B) is found, where γ^? is an empirical magnetoresistivity coefficient and μ₀^? the electron mobility with B = 0. Further, it is shown that theories presently existing on the physical magnetoresistivity are not able to explain these results.     

Quantum properties of two-dimensional electron gas in the inversion layer of Hg1−xCdxTe bicyrstals

The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p-type Hg_1−xCd_xTe bicrystals are investigated. The results clearly demonstrate the existence of a two-dimensional degenerate n-type inversion layer in the vicinity of the grain boundary. Hydrostatic pressure up to 10³ MPa is used to characterize the properties of the two-dimensional electron gas in the inversion layer. At atmospheric pressure three series of quantum oscillations are revealled, indicating that tthree electric subbands are occupied. From quantum oscilations of the magnetoresistivity the characteristics parameters of the electric subbands (subband populations n_si, subband energies E_F−E_i, effective electron masses m^*_ci) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied A simple theoretical model based on the triangular-well approximation and taking into account the pressure dependence of the energy band structure of Hg_1−xCd_xTe is use to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters.     

Magnetic and electrical properties of amorphous PdCoP alloys

Magnetic susceptibility and electrical resistivity measurements were performed (Pd_100?xCo_x)₈₀P₂₀ alloys where 15 < x < 50. The magnetic properties show that these alloys undergo a ferromagnetic transition between 272 and 399 K as the cobalt concentration increases from 15 to 50 atomic %. Below 20 atomic % Co the short-range exchange interactions which produce the ferromagnetism are unable to establish a long-range magnetic order and a peak in the magnetization shows up at the lowest temperature range under an applied field of 6.0 kOe. The electrical resistivity of these alloys has been measured from 4.2 K up to the vinicity of the melting point (900 K). The electrical resistivity data could be interpreted by the coexistence fo a Kondo-like minimum and ferromagnetism. The minimum becomes less important as the transition metal concentration increases. The coefficients of In T and T² become smaller and concentration dependent. The spin ordering in such alloys can be simulated as either the ordering due to an applied “external field” or as an increase in “internal fields”. These are due to an increase in transition metal concentration. The negative magnetoresistivity is a strong indication of the existence of localized moment.     

Anisotropic k-ƒ interactions from spin-orbit coupled 5d intermediate states

The anisotropy of the conduction electron-4? local moment interaction ($\text{k-?}$) gives rise to anisotropic transport effects. The contribution from the orbital character of the 4? moment has been well documented by magnetotransport studies on noble metals containing non-S state rare-earth ions. To determine whether there is an additional contribution to the anisotropy from the spin-orbit coupled 5d electron states we have studied the magnetoresistivity of Ag: Gd alloys. We have not found any significant anisotropy of the magnetoresistivity. By comparing this result and previous Hall effect and magnetoresistivity data on noble metal-rare earth alloys with our model calculation, we come to the conclusion that the spin-orbit splitting of the 5d virtual bound state is relatively small. We discuss the details of the resulting anisotropy of the $\text{k-?}$ interaction.     

Determination of isotope shift crossed-second-order-effects and hyperfine-structure parameters in the Eu I configuration 4f 7 6s7s

In the Eu I configuration 4f ⁷(⁸ S)6s7s the isotope shift (IS) and hyperfine-structure (hfs) of the levelse ⁸ S _7/2 andf ⁸ S _7/2 were determined from the transitions 684.5 nm, 733.7 nm and 821.0 nm to 4f ⁷6s6p. Together with experimental results of our previous measurements a theoretical analysis of the IS and hfs for the complete configuration 4f ⁷ 6s7s can now be carried out. From the IS of the four 6s7s-levels we evaluated the two crossed-second-order-parametersg ₃(4f,6s)= ?l.l(l)mK andg ₃(4f, 7s)= ?0.1(l)mK. The ratiog ₃/G ₃ is determined for various Eu configurations and found to be equal to 5.6(3)·10^?6 in complete agreement with a theoretical value following from Hartree-Fock calculations. The single electron hfs splitting constantsa ¹⁰(4f)= ?1.9 (3) mK,a ¹⁰(6s)=396(3)mK, anda ¹⁰(7s)=65(3)mK are also determined and compared with those of other Eu configurations.     

Current-conducting properties of paper consisting of multiwall carbon nanotubes

Electrical conductivity σ(T) of the paper consisting of multiwalled carbon nanotubes (MWCNTs) is studied in the temperature range 4.2-295 K, and its magnetoresistivity ρ(B) at various temperatures in magnetic fields up to 9 T is analyzed. The temperature dependence of the paper electrical conductivity σ(T) exhibits two-dimensional quantum corrections to the conductivity below 10 K. The dependences of negative magnetoresistivity ρ(B) measured at various temperatures are used to estimate the wavefunction phase breakdown length L _φ of conduction electrons and to obtain the temperature dependence L _φ = constT ^?p/2, where p ≈ 1/3. Similar dependences of electrical conductivity σ(T), magnetoresistivity ρ(B), and phase breakdown length L _φ(T) are detected for the initial MWCNTs used to prepare the paper.     

Thermal correction to resistivity in dilute Si-MOSFET two-dimensional systems

Neglecting electron-electron interactions and quantum interference effects, we calculate the classical resistivity of a two-dimensional electron (hole) gas, taking into account the degeneracy and the thermal correction due to the combined Peltier and Seebeck effects. The resistivity is found to be a universal function of the temperature, expressed in units of (h/e²)(k_Fl)^?1. Analysis of the compressibility and thermopower points to the thermodynamic nature of the metal-insulator transition in two-dimensional systems. We reproduce the beating pattern of Shubnikov-de Haas oscillations in both the crossed field configuration and Si-MOSFET valley splitting cases. The consequences of the integer quantum Hall effect in a dilute Si-MOSFET two-dimensional electron gas are discussed. The giant parallel magnetoresistivity is argued to result from the magnetic-field-driven disorder.     

Cooling dilute 3He4He mixtures to 0.6 mK

We have cooled a ³He⁴He solution to the lowest temperatures yet achieved, 0.58 mK, and find no evidence for a superfluid transition in the dissolved ³He. We have measured the thermal boundary resistance between this solution and sintered 700 Å silver powder, and find that R is proportional to T^?2 between 0.8 mK and 4 mK.     

Isotope shift in osmium I: Experiment and theory

The isotope shift in the arc spectrum of osmium was studied in 10 lines for the highly enriched isotopes¹⁸⁸Os and¹⁹²Os and in 2 lines for natural¹⁹⁰Os by means of a photoelectric recording Fabry-Perot spectrometer with digital data processing. The observed shifts were analyzed by means of the parametric method. The field shift of 5d ⁷6s ⁵ F is 53.4 (9.6) mK larger than that of³ F, thus showing the influence of crossed-second-order effects produced by the interaction of the electrostatic operator and the field shift operator. Spin dependent effects were also able to be evaluated. The corresponding parameterz _s for the configuration 5d ⁷6s was found to be 2.5 (2) mK. The experimental data are compared with results from non-relativistic Hartree-Fock calculations. Except for a scaling factorS ^*(Z)=1.489 the calculated electron densities describe the measured isotope shifts of this work and of other authors.     

PVT properties of sulfur-hexafluoride in the gas-liquid critical region

The PVT properties of sulfur hexafluoride in the critical region have been measured by using a combination of the Burnett and the isochoric methods. The measurement of one reference PV-isotherm at about 333 K was performed by the Burnett method of repeated expansions; the measurement of a large number of PT quasi-isochores between 313 and 333 K relied on the so-called isochoric method. An important feature of the data analysis is the application of several consistency criteria to the least-squares analysis for polynomial representation which made it possible to determine reliable values of the Burnett constants and the virial coefficients. The reference isotherm with 105 data points covers a pressure range between 1 and 100 bar and a density range up to 1.2 g cm^?3. The 21 isochoric runs with densities between 0.1 and 1.2 g cm^?3 contain 220 data points. Except for the region very close to the critical point, the accuracy of the measurements is estimated to be better than 0.01% in the pressure, 0.02% in the density and 1 mK in the temperature.     

Absence of low-temperature anomaly on the melting curve of <Superscript>4</Superscript>He

The melting pressure and pressure in the liquid at a constant density of ultrapure ⁴He (0.3 ppb of ³He impurities) have been measured with an accuracy of about 0.5 μbar in the temperature range from 10 to 320 mK. The measurements show that the anomaly on the melting curve below 80 mK, which was recently observed [I. A. Todoshchenko et al., Phys. Rev. Lett. 97, 165302 (2006)], is entirely due to an anomaly in the elastic modulus of Be-Cu from which our pressure gauge is made. Thus, the melting pressure of ⁴He follows the T ⁴ law due to phonons in the whole temperature range from 10 to 320 mK without any attribute of a supersolid transition. The text was submitted by the authors in English.     

Thermal resistance of sintered powder-liquid 3He boundary

Heat transfer between normal liquid ³He and sintered powders is investigated in terms of the Landau Fermi liquid theory. It is shown that the coupling between zero sound in ³He and low energy vibrational modes in sinter gives the extra contribution to the heat transfer below about 10mK. Theoretical results are compared with experimental data from 2mK to 100mK.     

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×10¹⁴ Ar/cm². A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.

     

Optical isotope shifts in neodymium

Isotope shifts have been measured in Nd II from which the shifts between pure configurations 4f ⁴ 6s and 4f ⁴ 5d can be determined. The specific mass shift for such a “transition” was estimated to be + 3 mK for a change of two neutrons. By comparison with electronic X-ray isotope shifts the following values were obtained for the change in the nuclear charge distributionδ〈r ²〉 [fm²]: (142, 144) 0.277; (144, 146) 0.257; (146, 148) 0.286; (148, 150) 0.381; (142, 143) 0.130; (144, 145) 0.111. Field shifts in several optical transitions have been compared with values of ¦ψ(0)¦² obtained from Hartree-Fock wave functions; agreement is good. Other specific mass shifts have been estimated 4f ⁴ 6s? 4f ⁴ 6p, ?1 mK; 4f ⁴ 6s? 4f ³ 5d ², ?30 mK. These values are in good agreement with calculated values of ?1.1 and ?30.6 mK.     

Pressure dependence of the superconducting transition temperature of a (Mo0.6Ru0.4)86B14 metallic glass

We have studied the pressure dependence of the superconducting transition temperature of amorphous (Mo_0.6Ru_0.4)₈₆B₁₄ for hydrostatic pressures up to P ～ 9 kbar. The transition temperature T_c decreases with pressure at a rate dT_c/dP=-(9±1) mK kbar^-1. We estimate the Grüneisen parameter and the volume dependence of the electron-phonon coupling constant.     

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

A study on electron spin resonance (ESR) spectroscopic determination of exchange interactions in organic oligoradicals is given. When the intramolecular exchange couplingJ between, unpaired electron spins in nitroxide-based oligoradicals falls within the order of 10 Oe (1 mK or 10^?3 cm^?1 forg=2), which is on the same order as the hyperfine couplingA of magnetic nuclei such as nitrogen atoms of nitroxide radicals, the magnitude ofJ can be determined from the hyperfine splitting pattern of ESR spectra in solutions. This range of the exchange couplingJ is not detectable in conventional magnetic susceptibility measurements. We demonstrate an application of hyperfine ESR spectroscopy as a probe for the exchange coupling to a series of organic oligoradicals, which the authors have recently developed as building blocks for molecule-based magnetic materials.     

Cold-electron bolometer arrays

To improve electron cooling, expand the dynamic range, and match the input and output impedances, series/parallel arrays of cold-electron bolometers have been developed, manufactured, and measured at temperatures from 50 to 350 mK. The bolometers are integrated into cross-slot antennas to analyze the polarization of cosmic microwave background radiation at a frequency of 345 GHz. The maximum temperature response is 6.5 μV/mK. The noise-equivalent electric power at a temperature of 300 mK is 1.2 × 10^?17 W/Hz^1/2.