Metal-insulator transition induced by the magnetic field in n-type GaSb

The metal-insulator (MI) transition induced by a magnetic field was evidenced for the first time in compensated n-type GaSb layers grown by molecular beam epitaxy. The free electron densities were in the low 10¹⁶ cm⁻³ range or even slightly lower, so that the zero-field 3D electron gas was degenerate and, at the B_MI magnetic field of the MI transition, it populates only the spin-split 0⁽⁺⁾ Landau level (extreme quantum limit). On the metallic side of the MI transition a T^1/3 dependence of the conductivity was assumed to fit the low-T data and to estimate the B_MI value, which resulted of 9.1 T in the purest sample. The MI transition manifests in a strong increase of the diagonal resistivity with the magnetic field, but not of the Hall coefficient, suggesting that the apparent electron density is practically constant, whereas the mobility varies strongly. The evidence of a maximum in the temperature dependence of the Hall coefficient has been explained through a two channels transport mechanism involving localized and extended states.     

A germanium oscillator in a pulsed magnetic field

Experimental data which confirms the presence of hysteresis of the magnetic threshold field of the helical instability of the plasma in a germanium oscillator are presented. It is shown that hysteresis of the threshold magnetic field is due to the inertia of the change in the effective lifetime of the charge carriers in the specimen when the magnetic field is increased and reduced. The dependence of the hysteresis of the threshold magnetic field on the electric field strength, the magnetic field, and the temperature is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–41, July, 1982.The authors thank R. I. Bashirov, and K. M. Aliev for making it possible to carry out the measurements in pulsed magnetic fields, and G. P. Il'yukevich for his technical help.     

Fine structure of shallow donor lines in germanium induced by magnetic field

Photoconductivity spectra of Ge doped with Sb and P were investigated in a magnetic field (H) at the temperature T = 4.2K. Measurements were performed in the Voigt configuration (H ∥ [111]). Fine structure of lines connected with optical transitions from the ground to the excited states of shallow donors due to spin splitting of impurity energy states were observed.     

Absolute negative resistance in a nonequilibrium two-dimensional electron system in a strong magnetic field

The effect of microwave electromagnetic radiation on the resistance of the 2D electron gas in a GaAs/AlAs heterostructure in a strong magnetic field is investigated. It is shown that, under the nonequilibrium conditions caused by microwave radiation, the aforementioned 2D system exhibits giant oscillations of its resistance with varying magnetic field. When the measuring current density is small, an increase in the microwave power leads to the appearance of an absolute negative resistance at the main minimum of these oscillations, which lies near the cyclotron resonance. The experimental data are found to be in qualitative agreement with the theory of multiphoton photoinduced impurity scattering [J. Inarrea and G. Platero, Appl. Phys. Lett. 89, 052109 (2006)].     

Absolute negative resistance in a nonequilibrium two-dimensional electron system in a strong magnetic field

The effect of microwave electromagnetic radiation on the resistance of the 2D electron gas in a GaAs/AlAs heterostructure in a strong magnetic field is investigated. It is shown that, under the nonequilibrium conditions caused by microwave radiation, the aforementioned 2D system exhibits giant oscillations of its resistance with varying magnetic field. When the measuring current density is small, an increase in the microwave power leads to the appearance of an absolute negative resistance at the main minimum of these oscillations, which lies near the cyclotron resonance. The experimental data are found to be in qualitative agreement with the theory of multiphoton photoinduced impurity scattering [J. Inarrea and G. Platero, Appl. Phys. Lett. 89, 052109 (2006)]. Original Russian Text ? A.A. Bykov, D.R. Islamov, D.V. Nomokonov, A.K. Bakarov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 9, pp. 695–698.     

The excitonic spectrum of germanium in a high magnetic field

In recently reported experiments with uniaxially deformed germanium in a magnetic field [V. B. Timofeev and A. V. Chernenko, JETP Lett. 61, 617 (1995)], it was found that applying a magnetic field of sufficiently high intensity results in the appearance of a new line in the optical spectrum of the excitons. In the present paper a mechanism is proposed which can provide an explanation for this experimentally observed spectral feature. The new spectral line may be attributed to the formation of strongly bound biexcitonic molecules in the quantum state ³Π_u. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 405–409 (25 March 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

ODD parity donor levels of germanium in a magnetic field

The lowest three odd parity states of Ge donors are calculated in the effective mass approximation as functions of magnetic field strength for fields in the (111) and (100) directions. This extends our earlier calculations of 1s and 2s-like Ge donor states. No simplifying assumptions are introduced —we attempt to take explicitly into account the lack of cylindrical symmetry of the effective mass Hamiltonian in our choice of trial functions. Our results appear to agree reasonably well with measured transition energies of Nisida and Horii.     

PAC-study of defects in n-type germanium

Using perturbed angular correlations of γ rays the behaviour of Frenkel defects in n-type germanium is studied.¹¹¹In/¹¹¹Cd probes either serve as primary knock-on atoms in the production of Frenkel defects by neutrino recoil or as trapping agents for defects produced by electron irradiation. The neutrino recoil process leads to a defect which is characterized by vQ=e²qQ/h=42(2) MHz (η=0.6), while a defect with vQ=423(1) MHz (η=0) is observed after electron irradiation and thermal annealing.     

Field dependent central cell correction in germanium in a magnetic field

We report calculations of the energies of 1s and 2s donor levels in Ge as functions of magnetic field. The Ge 1s and 2s donor eigenstates in fields along the (111) and (100) directions were studied in the effective mass approximation by using variational wave functions. We have made none of the artificial assumptions invoked by previous authors for simplifyingsuch effective mass calculations. To account for the central cell shifts of these levels we generalize to the case of donors in Ge, in a model which has been very successful in predicting the magnetic field dependence of donor central cell corrections in GaAs. Our results cast some doubt on certain recent transition assignments of Gershenzon and Gol'tsman.     

A multisublattice magnetic phase induced by external field in a singlet magnet

The theory of magnetization in a longitudinal magnetic field is developed for an easy-plane multisublattice antiferromagnet with a singlet ground state and a strong single-ion anisotropy exceeding the magnitude of exchange interaction. The magnetic-field-induced phase transition from the singlet (magnetically dis-ordered) state to a multisublattice antiferromagnetic state represents a displacive magnetic phase transition. At T=0, this transition proceeds continuously and belongs to second-order phase transitions, while at T ≠0, the behavior changes to jumplike and the process becomes the first-order phase transition.     

Two-dimensional hydrogen negative ion in a magnetic field

Making use of the adiabatic hyperspherical approach, we report a calculation for the energy spectrum of the ground and low-excited states of a two-dimensional hydrogen negative ion H^{-} in a magnetic field. The results show that the ground and low-excited states of H^{-} in low-dimensional space are more stable than those in three-dimensional space and there may exist more bound states.     

Hall resistance anomalies induced by a radiation field

A study is made of the four-terminal Hall junction under the influence of a radiation field. The frequency of the radiation field is tuned to a transition between the energy of a bound state below a conduction subband and the Fermi energy of the incident electrons. Radiation-field-induced resonant dips of the Hall resistance are exhibited at low magnetic fields. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 403–408 (25 September 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Palladium-vacancy pairs in p-type and n-type germanium

Time differential perturbed angular correlation spectroscopy was performed for n-type and p-type germanium samples that had been recoil-implanted with the probe ¹⁰⁰Pd/¹⁰⁰Rh. Two different measurements with the detectors aligned along <100> and <110> crystallographic directions of germanium confirm that the palladium probe pairs with the nearest neighbour vacancy and not a dopant. The pairs interact with a coupling constant of υ _Q = 10.7(2) MHz and this agrees with what has been observed in undoped Ge. This further suggests that the palladium pairs with a vacancy in germanium, doped or un-doped. It was also observed that there are more Pd-V pairs in Ga-doped than there are in Sb-doped Ge. DFT calculations of the binding energies of the Pd-defect complexes support the experimental observations.     

舰船感应磁场预测的一种新方法

提出一种基于磁化强度的舰船感应磁场预测法.首先证明了一个基于磁化观点的铁磁物体内部磁场强度计算公式,随后通过该公式导出了点函数去磁张量的概念并证明了它的一些性质,最后利用此公式构造了一个预测非均匀外场中舰船感应磁场的新方法——磁化强度法,且在该方法中用到了点函数去磁张量.与传统的舰船感应磁场预测方法相比,磁化强度法具有计算量小、精度高、物理意义明显等特点.船模数值试验验证了本方法.     

Stabilization of electron-hole liquid in uniaxially strained germanium in a strong magnetic field

Luminescence spectra of uniaxially and uniformly strained high-purity germanium crystals at liquid-helium temperatures in a magnetic field of up to 14 T have been investigated. In strongly strained Ge crystals, a new line has been detected on the low-energy side of the excitonline in magnetic fields higher than 4 T. Studies of this line’s characteristics as functions of pressure, temperature, and magnetic field have led us to conclude that its presence is due to recombination of electron-hole pairs in an electron-hole liquid. The experimental data suggest that the metallic electron-hole liquid is stabilized in a strong magnetic field. By approximating the shape of the newly detected line using the model of metallic electron-hole liquid, we have obtained the electron-hole liquid density n _EHL(B) and Fermi energies E _Fe,h of electrons and holes. The liquid binding energy ø as a function of magnetic field has been estimated.     

Symmetry breaking induced by a magnetic field in a quasi-two-dimensional d-wave superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time reversal symmetry breaking SDW order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity in might be ascribed to this effect. Received 7 May 1999 and Received in final form 13 August 1999     

Anisotropy characteristics in a Permalloy film induced by a nonuniform magnetic field

Inhomogeneities were observed for the first time in the magnetic structure of a thin Permalloy film, induced by a strongly nonuniform magnetic field applied in the plane of the substrate during fabrication of the samples. The films were obtained by vacuum deposition using a molecular-beam epitaxy system. A nonuniform field was created on the substrate using four samarium-cobalt magnets. The anisotropy of local sections of the samples was measured using a scanning-ferromagnetic-resonance spectrometer. A strong correlation was observed between the distribution of the magnitude and direction of the local magnetic anisotropy of the film and the magnetic-field distribution in the plane of the substrate. Fiz. Tverd. Tela (St. Petersburg) 40, 1291–1293 (July 1998)     

Electric conduction in n-type germanium and cadmium sulfide

The impurity conduction of n-type Ge and CdS is calculated via a previously developed theory for impurity bands in doped semiconductors. Rough agreement with experimental data over a wide range of impurity concentration is found. The comparison with AMO-MT calculation shows a large enhancement due to a stronger electron correlation.     

Strong n-type molecule as low bias negative differential resistance device predicted by first-principles study

A first-principles study of the transport properties of two thiolated pentacenes sandwiching ethyl is performed. The thiolated pentacene molecule shows strong n-type characteristics when contact Ag lead because of low work function about metal Ag. A strong negative differential resistance (NDR) effect with large peak-to-valley ratio of 758% is present under low bias. Our investigations indicate that strong n- or p-type molecules can be used as low bias molecular NDR devices and that the molecular NDR effect based on molecular-level leaving not on molecular-level crossing has no hysteresis.