Electronic structure of paramagnetic In<Subscript>1-x</Subscript>Mn<Subscript>x</Subscript> As nanowires

The electronic structure, spin splitting energies, and g factors of paramagnetic In_1-xMn_xAs nanowires under magnetic and electric fields are investigated theoretically including the sp-d exchange interaction between the carriers and the magnetic ion. We find that the effective g factor changes dramatically with the magnetic field. The spin splitting due to the sp-d exchange interaction counteracts the Zeeman spin splitting. The effective g factor can be tuned to zero by the external magnetic field. There is also spin splitting under an electric field due to the Rashba spin-orbit coupling which is a relativistic effect. The spin-degenerated bands split at nonzero k_z (k_z is the wave vector in the wire direction), and the spin-splitting bands cross at k_z = 0, whose k_z-positive part and negative part are symmetrical. A proper magnetic field makes the k_z-positive part and negative part of the bands asymmetrical, and the bands cross at nonzero k_z. In the absence of magnetic field, the electron Rashba coefficient increases almost linearly with the electric field, while the hole Rashba coefficient increases at first and then decreases as the electric field increases. The hole Rashba coefficient can be tuned to zero by the electric field.     

Magnetic-field dependent phonon states in paramagnetic CeF3

Raman scattering experiments in paramagnetic uniaxial CeF₃ at helium temperature demonstrate a splitting of some degenerate (E_g)-phonon states in an external magnetic field parallel to the crystal axis. A linear splitting is observed in low fields, followed by a field independent (saturation) splitting in high fields. In addition, changes in the Raman scattering efficiencies and a reduction of the line width of phonon transitions are observed with increasing magnetic fields. No such effects are observed for magnetic fields perpendicular to the crystal axis. The splittings of degenerate phonon modes are related to the paramagnetic saturation 〈S_z〉.     

Zeeman effects on d-wave superconductor and tunneling spectrum in normal-metal/d-wave superconductor tunnel junction

We study the Zeeman effect on the d-wave superconductor and tunneling spectrum in normal-metal(N)/d-wave superconductor(S) junction by applying a Zeeman magnetic field to the S. It is shown that: (1) the Zeeman magnetic field can lead to the S gap decreasing, and with the increase in Zeeman energy, the superconducting state is changed to the normal state, exhibiting a first-order phase transition; (2) the Zeeman magnetic field may make the zero-bias conductance peak split into two peaks, and the energy difference between the two splitting peaks in the conductance spectrum is equal to 2h ₀ (h ₀ is the Zeeman energy); (3) both the barrier strength of interface scattering and the temperature can lower the magnitudes of splitting peaks, of which the barrier strength can lead to the splitting peaks becoming sharp and the temperature can smear out the peaks, however, neither of them can influence the Zeeman effect.     

Theoretical analysis of the oscillatory gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors under magnetic quantization

An attempt is made to investigate theoretically the gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors under both weak and strong electric field limits in the presence of a quantizing magnetic field, takingn-channel inversion layers on p-type Cd GaAs₂ as examples. It is found, on the basis of the newly derived 2D electron spectra in inversion layers on the above class of semiconductors, for both weak and strong electric field limits, that the gate capacitances oscillate with the quantizing magnetic field and the crystal field splitting parameter effectively enhances the oscillatory spikes. It has also been observed that the oscillatory behaviour is in qualitative agreement with experimental observation as reported elsewhere for MOS structure of Hg_1–xCd_xTe. In addition, the corresponding results for inversion layers on parabolic semi-conductors are also obtained from the expressions derived.     

Double nuclear magnetic resonance in the weak ferromagnet YCrO3

Applications of 2D-NMR spectroscopy to measurements of the quadrupole splitting in magnetic materials are discussed using the weak ferromagnet YCrO₃ as a model system. A simple qualitative dissussion and results from computersimulations are given for various experiments. In systems with distributed electric field gradients the method provides a unique way to measure hyperfine field, quadrupole splitting and correlations between these local parameters.     

Spin splitting in HgTe/CdHgTe (013) quantum well heterostructures

The electron transport and cyclotron resonance in a one-sided selectively doped HgTe/CdHgTe (013) heterostructure with a 15-nm quantum well with an inverted band structure have been investigated. The modulation of the Shubnikov-de Haas oscillations has been observed, and the spin splitting in zero magnetic field has been found to be about 30 meV. A large Δm _c/m _c ≃ 0.12 splitting of the cyclotron resonance line has been discovered and shown to be due to both the spin splitting and the strong nonparabolicity of the dispersion relation in the conduction band.     

Zero-field splitting of <Superscript>4</Superscript><Emphasis Type="Italic">T</Emphasis><Subscript>2</Subscript> term for 3d<Superscript>3</Superscript> ions in tetragonal symmetry

By taking into account slight interactions, i.e. spin-spin, spin-other-orbit and orbit-orbit interactions, in addition to spin-orbit interaction, the zero-field splitting of ⁴ T ₂ state for 3d³ ions at tetragonal symmetry has been studied. The convergence of the approximation perturbation formula of ⁴ T ₂ state for 3d³ ions at tetragonal symmetry has been investigated, and the contributions to zero-field splitting arising from magnetic interaction and tetragonal crystal field are discussed. It is found that there exists combined mechanism between magnetic interactions and tetragonal crystal field.      

Magnetic resonance, phase transition, and phase coexistence in a highly doped La0.8Sr0.2MnO3 manganite near the Curie point

Magnetic resonance and microwave impedance are studied in a highly doped La_0.8Sr_0.2MnO₃ manganite near the Curie temperature. A splitting of the resonance line is observed in the temperature region 6° below the temperature corresponding to the maximum impedance at zero magnetic field. The microwave impedance exhibits a hysteretic behavior in increasing and decreasing temperature runs with jumps at the ends of a 2°-wide temperature interval. The splitting of magnetic resonance occurs immediately above the temperature corresponding to the impedance jump in zero magnetic field. The jumps and the hysteretic behavior of the impedance are interpreted as a manifestation of the magnetic structure phase transition of the first order.     

两个子带占据的In0.53Ga0.47As/In0.52Al0.48As量子阱中填充因子的变化规律

研究了低温(15K)和强磁场(0—13T)条件下, InP基In_053Ga_047As/In_052Al_048As量子阱中电子占据两个子带时填充因子随磁场的变化规律.结果表明,在电子自旋分裂能远小于朗道能级展宽的情况下,如果两个子带分裂能是朗道分裂能的整数倍时,即ΔE₂₁=kω_c(其中k为整数),填充因子为偶数;当两个子带分裂能为朗道分裂能的半奇数倍时,即ΔE₂₁=(2k+1)ω_c/2,填充因子出现奇数. 关键词： 053Ga_047As/In_052Al_048As量子阱')" href="#">In_053Ga_047As/In_052Al_048As量子阱 填充因子 磁输运     

Theoretical study of the effective electron mass in ternary chalcopyrite semiconductors in the presence of crossed electric and magnetic fields

An attempt is made to investigate theoretically the effective electron mass in ternary chalcopyrite semiconductors at low temperatures on the basis of a newly derived dispersion relation of the conduction electrons under cross fields for the more generalized case which occurs from the consideration of the various types of anisotropies in the energy spectrum. It is found, taking degeneraten-CdGeAs₂ as an example, that the effective electron mass at the Fermi level along the direction of magnetic quantization depends on both the Fermi energy and the magnetic quantum number due to the combined influence of the crystal field splitting parameter and the anisotropic spin-orbit splitting parameter respectively, resulting in different effective masses at the Fermi level corresponding to different magnetic sub-bands. It is also observed that the same mass at the Fermi level in the direction normal to both magnetic and electric fields also varies both with Fermi energy and magnetic sub-band index, and the characteristic feature of cross-fields is to introduce the index-dependent oscillatory mass anisotropy. The theoretical results are in good agreement with the experimental observations as reported elsewhere.     

EPR,optical and superposition model study of Mn2+ doped L+ glutamic acid

Electron paramagnetic resonance (EPR) study of Mn²⁺ doped L+ glutamic acid single crystal is done at room temperature. Four interstitial sites are observed and the spin Hamiltonian parameters are calculated with the help of large number of resonant lines for various angular positions of external magnetic field. The optical absorption study is also done at room temperature. The energy values for different orbital levels are calculated, and observed bands are assigned as transitions from ⁶A_1g(s) ground state to various excited states. With the help of these assigned bands, Racah inter–electronic repulsion parameters B = 869 cm^?1, C = 2080 cm^?1 and cubic crystal field splitting parameter Dq = 730 cm^?1 are calculated. Zero field splitting (ZFS) parameters D and E are calculated by the perturbation formulae and crystal field parameters obtained using superposition model. The calculated values of ZFS parameters are in good agreement with the experimental values obtained by EPR.     

Anomalous asymmetry of magnetoresistance in NbSe3 single crystals

A pronounced asymmetry of magnetoresistance with respect to the magnetic field direction is observed for NbSe₃ crystals placed in a magnetic field perpendicular to their conducting planes. It is shown that the effect persists in a wide temperature range and manifests itself starting from a certain magnetic induction value B ₀, which at T = 4.2 K corresponds to the transition to the quantum limit, i.e., to the state where the Landau level splitting exceeds the temperature.     

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (BiSb)Telayered single crystals near the quantum limit

On bulk layered single crystals (Bi_0.25Sb_0.75)₂Te₃ with a hole concentration cm^-3 and a mobility cm²/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m _c = 0.12m ₀ is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be . Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998     

Excitons and linear optical spectra of E33 and E44 in single wall carbon nanotubes under axial magnetic field

The E₃₃ and E₄₄ optical spectra of semiconducting single-walled carbon nanotubes under axial magnetic field (B) are studied using the tight-binding model, which also takes into account the exciton effect. It is found that the E₃₃ and E₄₄ splitting, induced by the axial magnetic field, is line increased with magnetic field, which can be described by the splitting rate. Also by investigation of the dependence of splitting rate, we found that it shows a clear (2n+m) family behavior besides the diameter dependence, which can be used as a supplemental tool to identify the tubes used in the experiment, and is expected to be detected by the future experiment.     

Effect of interlayer tunneling on the electronic structure of bilayer cuprates and quantum phase transitions in carrier concentration and high magnetic field

We present a theoretical study of the electronic structure of bilayer HTSC cuprates and its evolution under doping and in a high magnetic field. Analysis is based on the t-t′-t″-J* model in the generalized Hartree-Fock approximation. Possibility of tunneling between CuO2 layers is taken into account in the form of a nonzero integral of hopping between the orbitals of adjacent planes and is included in the scheme of the cluster form of perturbation theory. The main effect of the coupling between two CuO₂ layers in a unit cell is the bilayer splitting manifested in the presence of antibonding and bonding bands formed by a combination of identical bands of the layers themselves. A change in the doping level induces reconstruction of the band structure and the Fermi surface, which gives rise to a number of quantum phase transitions. A high external magnetic field leads to a fundamentally different form of electronic structure. Quantum phase transitions in the field are observed not only under doping, but also upon a variation of the field magnitude. Because of tunneling between the layers, quantum transitions are also split; as a result, a more complex sequence of the Lifshitz transitions than in single-layer structures is observed.     

Magnetic field dependent splitting of doubly degenerate phonon states in anhydrous cerium-trichloride

The Raman spectra of single crystals of hexagonal CeCl₃ have been investigated atT=2K in external magnetic fieldsB up to 6 T. The crystal field states of the 4f ¹(² F _5/2)-configuration of Ce³⁺ show a linear Zeeman-splitting. Two degenerate phonon states (197 cm^–1(E _1g), 109 cm^–1(E _2g)) also split in the magnetic field. ForB parallel to the optic axisZ the field dependence of the splitting is similar to the behaviour reported earlier for Ce F₃ and NdF₃ (linear splitting at low fields, which is followed by a saturation at high fields). ForBZ a splitting of the same phonons proportional toB ² is observed in CeCl₃, which was not found in the other compounds. The linewidths of the electronic transitions and of the split phonon components are reduced with increasing magnetic fieldstrength.The field- and temperature dependences of the phonon energies can be explained quantitatively using results of the theory of the 4f-electron-phonon interaction as developed for the cooperative Jahn-Teller-effect or for the magneto-elastic interaction. The experimental results forBZ require an interaction Hamiltonian which is bilinear in the electronic and phonon operators, respectively. The conclusions are supported by group theoretical considerations.The experiments described here have been performed at the Technische Hochschule Darmstadt, Institut für Festkörperphysik II, Fachgebiet Technische Physik as a project of the Sonderforschungsbereich Festkörperspektroskopie SFB65, supported by the Deutsche Forschungsgemeinschaft     

Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe₃(BO₃)₄ have been studied in the region of ⁷F₆ → ⁵D₄ transition in Tb³⁺ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb³⁺ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb³⁺ ion environment only in the excited state of the Tb³⁺ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb³⁺ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D ₃ symmetry approximation) consists of two close singlet states of A ₁ and A ₂ type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe₃(BO₃)₄ structural phase transition. The temperature interval of coexistence of the phases is about 3 K.     

Magneto-optical study of Er-related center in selectively doped Si:Er

Photoluminescence at λ=1.54 μm from an Er³⁺-related center dominant in a sublimation MBE-grown multi-layer Si/Si:Er structure is investigated in magnetic fields up to 6 T. The magnetic-field-induced splitting is observed for all the main lines of the Er-related photoluminescence spectrum. For the most intense emission line, angular dependence of the splitting is measured in the (011) crystallographic plane of the sample. The effective g-tensor, corresponding to the difference between individual g-tensors of the lowest multiplets of the ground and the first excited states, is experimentally determined. In this way the symmetry of the Er-related optically active center dominant in the structure is found to be orthorhombic I (C_2v). From temperature dependence of the intensity of the magnetic field split components, individual g-tensors of the ground and the excited states are separated. No influence of the growth direction on the symmetry of Er-related center was found.     

Magnetic resonance measurements on Rb2MnCl4

The paper describes an experimental set-up for measuring the transmission in the millimeterwave range by employing a backward-wave-oscillator technique. We have studied magnetic excitations of the quasi-two-dimensional antiferromagnet Rb₂MnCl₄. An expected splitting of the zero field resonance has been observed which is probably due to an orthorhombic distortion.