Landau Quantization Effects Research Articles

Anomalous behavior of the upper critical field in extreme type-II superconductors at low temperatures

We present a detailed numerical calculation of the upper critical field H c2 ( T) for a bulk extreme type-II superconductor. Particular emphasis is placed on the high-field, low-temperature regime of the HT-phase diagram. In this regime, it is necessary to go beyond the standard semi-classical theory and include the effects of Landau quantization of the electronic motion on the superconducting state. The presence of Landau level quantization induces an upward curvature in H c2 ( T) at ∼10% of T c0 for those superconducting systems in which the slope of H c2 ( T) at T c0 is ≥0.2 T/K. We construct a simple analytical model that can account for this behavior based on the renormalization of the BCS coupling constant by the off-diagonal pairing of electrons on Landau levels.

Unconventional Superconductivity in Strong Magnetic Field

The Landau quantization effects are considered in low carrier concentration unconventional spin triplet p-wave superconductors in a high magnetic field region. The field dependence of the superconducting order parameter and the vortex lattice states for intra Landau level pairing are analyzed. The gap functions are calculated within mean field approximation. PACS numbers: 74.60.—w, 74.20.Fg, 71.70.Di, 74.62.—c

Landau quantization effects in superconductors

The influence of orbital quantization effects in a strong magnetic field in low carrier concentration singlets-wave and tripletp- wave superconductors are considered.

De Haas-van Alphen effect in the superconducting state

Quantum oscillations were first observed in the mixed state of superconductor, NbSe 2, by Graebner and Robbins in 1976. More recently, the investigation of a number of other materials has shown that de Haas-van Alphen effect oscillations persist below B c2 in many systems, so that quantum oscillations in the vortex state appear to be the rule rather than the exception. Such measurements demonstrate that the effects of Landau quantization persist in the mixed state of a clean type II superconductor. In this paper we review work on NbSe 2, V 3Si and Nb 3Sn, for which detailed measurements exist. We find that the principal effect of the superconducting order parameter is to reduce the amplitude of the oscillatory magnetisation. In principle, quantum oscilltory measurements of this type will give detailed information on the anisotropies of the superconducting state.

The effect of Landau quantization on cyclotron resonance in a non-parabolic quantum wells

Electron cyclotron resonance is studied in very deep quantum wells consisting of InAs between AlSb barriers. High electron mobility and strong conduction band non-parabolicity together with the small effective mass and the large effective g factor of this material enables the authors to observe simultaneous cyclotron transitions between adjacent sets of spin-split Landau states. Their experiments resolve spin-conserving transitions involving two or three different Landau levels depending on the filling factor. The results are compatible with a single-particle model.

Baber scattering in strong magnetic fields: The effect of Landau quantization.

With a basis of a two-band model, electron-electron scattering is studied in the presence of Landau quantization. The results are used to calculate the electrical resistivity of a transition metal (palladium) and of a semimetal (bismuth), assuming parallel electric and magnetic fields. The possibility is discussed of determining the importance of electron-electron scattering for the electrical resistivity in the controversial case of bismuth.

Surface studies using stem

Quantum oscillations were first observed in the mixed state of superconductor, NbSe2, by Graebner and Robbins in 1976. More recently, the investigation of a number of other materials has shown that de Haas-van Alphen effect oscillations persist below Bc2 in many systems, so that quantum oscillations in the vortex state appear to be the rule rather than the exception. Such measurements demonstrate that the effects of Landau quantization persist in the mixed state of a clean type II superconductor. In this paper we review work on NbSe2, V3Si and Nb3Sn, for which detailed measurements exist. We find that the principal effect of the superconducting order parameter is to reduce the amplitude of the oscillatory magnetisation. In principle, quantum oscilltory measurements of this type will give detailed information on the anisotropies of the superconducting state.

Nonlocal shift of the principle surface plasmon in quantizing magnetic field

The nonlocal surface plasmon dispersion relation in a quantizing magnetic field perpendicular to the surface is analysed, and the linear wave number shift of the principal surface plasmon mode is calculated in a way that incorporates Landau quantization effects for both the degenerate and nondegenerate cases. This mode is seen to be heavily damped when omega c>or= omega p in the electrostatic (nonretarded) regime.

Nonlocal surface plasmon spectrum in quantizing magnetic field: Surface Bernstein mode branch ( n=2)

The nonlocal surface plasmon spectrum in a quantizing magnetic field perpendicular to the surface has been found to have branches analogous to ‘Bernstein’ modes near multiples of the cyclotron frequency. The n=2 nonlocal surface ‘Bernstein’ mode is evaluated for low wavenumber, incorporating Landau quantization effects for degenerate and nondegenerate cases.

Bernstein modes and the quasiclassical model of the quantum plasma in magnetic field

A quasiclassical model is employed to calculate quantum magnetic field effects arising in conjunction with Bernstein mode plasmon resonances. This quasiclassical model incorporates Landau quantization effects in connection with degenerate (Fermi-Dirac) statistical averaging, while treating the selfconsistent internal plasma dynamics on a classical basis. The limitations of this model are discussed, and its usefulness is assessed.

Electronic Energy Gap in Ferromagnets Due to a Strong Internal Magnetic Field

The internal field in $3d$ ferromagnets is sufficiently strong that the motion of conduction electrons is affected to the extent that Landau quantization effects can be important. At low temperature we consider the scattering of conduction electrons from magnetic moments which are antiparallel to the direction of spontaneous magnetization and find an energy gap exists in the electronic energy spectrum. The current-carrying gap state gives rise to a frequency-dependent transverse conductivity which is enormous in the zero-frequency limit, suggesting an alternative mechanism for the spontaneous Hall effect in ferromagnets.

The application of the magnetophonon effect to a study of hot electron phenomena in insb

The magnetoresistance of three samples of high purity n-type insb(nd-na varying from 5*1013 to 5*1014 cm-3) is studied at lattice temperatures of 11 and 20 k with electric field strengths sufficient (>100 mv cm-1) to heat the electron distribution appreciably above the temperature of the lattice and at magnetic field strengths such that the effect of landau quantization is apparent. Two distinct types of magnetophonon extrema are observed, each having a different dependence on electric field and temperature. The first consists of a series of minima which are only observed when the electron temperature is in excess of about 20 k and which arises from the emission of long wavelength longitudinal optical (lo) phonons.

HIGH PULSED FIELD MAGNETORESISTANCE IN INDIUM ANTIMONIDE AND INDIUM ARSENIDE

Measurements of transverse magnetoresistance have been made using pulsed fields up to about 300 kilo-oersteds on oriented single-crystal samples of near-intrinsic indium antimonide and extrinsic indium arsenide at room temperature. At the maximum field, about a 400-fold resistivity increase was found in indium antimonide and about a 4-fold increase in indium arsenide. The variation with field can largely be accounted for by classical two-carrier conduction theory, even though ħωc/kT > 1 and [Formula: see text] for the electrons in indium antimonide. At the lower fields in indium antimonide the individual bands alone give no measurable contribution to the magnetoresistance, indicating that for the electrons at least, the relaxation time must be almost independent of energy. While no strong evidence of Landau quantization effects was apparent, the magnetoresistance values at the higher fields in general fell below the classical theoretical curve. This could be interpreted as a variation of the electron mobility at high fields such that approximately [Formula: see text].