De Haas-van Alphen Oscillations Research Articles

Theory of the Amplitude of the de Haas–van Alphen Oscillation in the Superconducting Mixed State: Effects of the Eddy Currents

The amplitude of the de Haas–van Alphen (dHvA) oscillation in the superconducting mixed state, which is measured by the field modulation method, is calculated. We investigate the effects of the superconducting eddy currents on the voltage signal from a pick-up coil, assuming that a finite conductivity, which may originate from the flux flow for example, exists in the mixed state. In a material which has a small Fermi surface, the Shubnikov–de Haas (SdH) effect contributes to the voltage signal in addition to the dHvA effect; therefore the amplitude of the voltage becomes larger than that of only the dHvA effect. In a material which has a large Fermi surface, the amplitude is hardly affected by the SdH effect and becomes smaller due to the skin effect. The present results have the same tendency with the experimental data of NbSe 2 as an example of a small Fermi surface and V 3 Si as an example of a large Fermi surface.

Sawtoothlike de Haas–van Alphen oscillations of a two-dimensional electron system

We present studies on the low-temperature magnetization of a two-dimensional electron system (2DES) in the integer quantum Hall-effect regime. The 2DES was formed in a modulation-doped AlGaAs/GaAs heterojunction. Using molecular-beam epitaxy it has been integrated into a highly sensitive micromechanical cantilever magnetometer. We observe de Haas–van Alphen oscillations at even filling factors up to ν=40 which for ν< 20 are almost perfectly sawtoothlike. Oscillations at odd filling factors ν=3,5,7, and 9 are due to the spin splitting of Landau levels. For a quantitative analysis of our data, calculations of the magnetization based on a model density of states (DOS) have been performed. We describe the DOS by narrow Gaussian broadened Landau levels with an energy-independent background. In particular we find that this background DOS increases linearly with ν. This behavior is qualitatively explained using the concept of edge channels. From our data we evaluate the level broadening and, at odd filling factors, the exchange-energy contribution to the spin splitting of Landau levels.

De Haas–van Alphen effect in two-dimensional and quasi-two-dimensional systems

We study the de Haas-van Alphen (dHvA) oscillation in two-dimensional and quasi-two-dimensional systems. We give a general formula of the dHvA oscillation in two-dimensional multi-band systems. By using this formula, the dHvA oscillation and its temperature-dependence for the two-band system are shown. By introducing the interlayer hopping $t_z$, we examine the crossover from the two-dimension, where the oscillation of the chemical potential plays an important role in the magnetization oscillation, to the three-dimension, where the oscillation of the chemical potential can be neglected as is well know as the Lifshitz and Kosevich formula. The crossover is seen at $4 t_z \sim 8 ta b H /\phi_0$, where a and b are lattice constants, $\phi_0$ is the flux quantum and 8t is the width of the total energy band. We also study the dHvA oscillation in quasi-two-dimensional magnetic breakdown systems. The quantum interference oscillations such as $\beta-\alpha$ oscillation as well as the fundamental oscillations are suppressed by the interlayer hopping $t_z$, while the $\beta+\alpha$ oscillation gradually increases as $t_z$ increases and it has a maximum at $t_z/t\approx 0.025$. This interesting dependence on the dimensionality can be observed in the quasi-two-dimensional organic conductors with uniaxial pressure.

Quantum interference oscillation and effect of spin in de Haas van Alphen effect in the quantum-well materials

In the heterojunction GaAs/Al 0.3Ga 0.7As with the two-dimensional (2D) one-band system and In x Ga 1− x As and GaAs/AlAs with 2D multi-band system, the de Haas van Alphen (dHvA) oscillation has been observed recently. The Lifshitz and Kosevich formula used conventionally in the dHvA effect is not appropriate to the 2D system. Therefore, we analytically give a formula on the dHvA oscillation in the 2D multi-band system. It is possible to obtain the cyclotron effective mass and the effective g-value exactly.

On the possibility of a radical decrease in the strength of many-body interactions in the organic metal α-(BETS)2 KHg(SCN)4

Behavior of the de Haas-van Alphen (dHvA) oscillations depending on the angle between the magnetic field direction and the perpendicular to conducting layers in the quasi-two-dimensional organic metal α-(BETS)2 KHg(SCN)4 was studied in detail. The angular dependence of the dHvA oscillation amplitude exhibits a series of minima (at ±43.2°, ±64.6°, and ±72.0°) related to the “zero spin” effect, through which it is possible to estimate the splitting factor. An analysis of this value suggests that many-body interactions in the compound studied are either absent or at least radically weakened.

Superconducting fluctuations and the reduced dimensionality of the organic superconductorκ−(BEDT−TTF)2Cu(NCS)2as observed through measurements of the de Haas–van Alphen effect

We report measurements of the de Haas-van Alphen (DHVA) effect and AC susceptibility in the layered organic superconductor $\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$. The amplitude of the DHVA oscillations is attenuated over a wide field range above the irreversibility line, B_irr(B), below which a rigid flux lattice is formed. Thus the DHVA effect provides a unique probe of the superconducting fluctuations at high fields in this material. We compare our measurements with other determinations of the superconducting phase diagram of $\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$.

Characterization of the Fermi surface of (BEDO-TTF)5[CsHg(SCN)4]2 by magnetoresistance measurements and tight-binding band structure calculations

Tight-binding band structure calculations as well as magnetoresistance and magnetization measurements were carried out in order to characterize the Fermi surface of the novel organic metal (BEDO-TTF)5[CsHg(SCN)4]2. The tight-binding calculations suggest that the Fermi surface can be described as containing two contributions: a closed two-dimensional portion associated with holes and an open pseudo-one-dimensional portion associated with electrons. Shubnikov-de Haas and de Haas-van Alphen oscillations were observed in magnetic fields of up to 14 T and temperatures of 1.5–4.2 K. Four frequencies (F1 = 650 T, F2 = 2600 T, F3 = 3200 T and F4 = 3850 T) associated with the Shubnikov-de Haas oscillations were found. The F1 and F4 frequencies are in good agreement with the calculated Fermi surface provided that the possibility of a magnetic breakdown effect is taken into account. It is also suggested that the F2 and F3 frequencies can be understood in the frame of the quantum interference effect.

Magneto Oscillations in Unconventional Superconductors well below Hc2

We have studied the De Haas-van Alphen oscillations of unconventional superconductor for magnetic field well below Hc2. We find that the amplitude of the oscillation is increased substantially relative to that of an s-wave gap material.

Fermi surface sheet-dependent superconductivity in 2H-NbSe2.

High-resolution angle-resolved photoemission spectroscopy was used to study the superconducting energy gap and changes in the spectral function across the superconducting transition in the quasi-two-dimensional superconductor 2H-NbSe2. The momentum dependence of the superconducting gap was determined on different Fermi surface sheets. The results indicate Fermi surface sheet-dependent superconductivity in this low-transition temperature multiband system and provide a description consistent with thermodynamic measurements and the anomalous de Haas-van Alphen oscillations observed in the superconducting phase. The present data suggest the importance of Fermi surface sheet-dependent superconductivity in explaining exotic superconductivity in other multiband systems with complex Fermi surface topology, such as the borides and f-electron superconductors.

De Haas-van Alphen effect in CeRh2Si2 under pressure

We observed de Haas-van Alphen (dHvA) oscillations in CeRh2Si2 at 1.3GPa, higher than the quantum critical pressure pc≃1.0GPa. Three observed dHvA branches correspond to the result of the 4f-itinerant model. Their cyclotron masses are large, being 24m0, 29m0 and 31m0, about 4 times larger than the corresponding band masses.

Superconducting fluctuation effect on the de Haas–van Alphen oscillations in the vortex liquid state of quasi-2D superconductors

The damping of the de Haas–van Alphen (dHvA) oscillations in the mixed state of a 2D superconductor is studied within a new analytical approach to the problem of vortex-lattice fluctuations at high magnetic fields. It is shown that in the ‘liquid’ state around mean field H c2( T), averaging over phase fluctuations leads to damping of the dHvA osillations, which can be well described by the random vortex lattice model. The calculated damping rate is in a good quantitative agreement with recent experiments carried out on a quasi-2D organic superconductor. It is predicted that deep in the mixed state, the freezing into an ordered vortex lattice is accompanied by a sharp upward turn in the slope of the ‘Dingle plot’.

De Haas–van Alphen effect in a two-dimensional electron system

With specially designed micromechanical cantilevers we have measured the magnetization of two-dimensional electron systems formed in an integrated single-layered AlGaAs/GaAs heterojunction. In samples of different mobility we have observed sawtooth-like de Haas–van Alphen oscillations which are evaluated with respect to the effect of the weak disorder.

De Haas-van Alphen effect in UIr

We have succeeded in growing a high-quality single crystal of UIr with the monoclinic structure by the Czochralski pulling method in a tetra-arc furnace. UIr is a ferromagnetic compound. Its Curie temperature TC is 46K and the magnetic moment is found to be oriented along the [101̄] direction by the magnetization measurement. The magnetic moment is 0.5μB/U. We have observed the de Haas-van Alphen oscillation. All the detected branches have heavy cyclotron effective masses ranging from 9.6 to 32m0. They are consistent with the electronic specific heat coefficient γ=48.5mJ/K2mol.

Fermi Surface and Magnetic Properties of the Antiferromagnet UIn3

We succeeded in growing a high-quality single crystal of UIn 3 by the self-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization, specific heat and de Haas-van Alphen (dHvA) oscillation. We confirmed the Néel temperature at T N =88 K from both the electrical resistivity and magnetic susceptibility measurements. We observed many dHvA branches. The Fermi surfaces are found to consist of closed Fermi surfaces and a multiply-connected Fermi surface. The cyclotron mass is relatively large, ranging from 9.8 to 33 m 0 .

Fourier analysis of the de Haas–van Alphen oscillations in two-dimensional electron systems with background reservoir states

A Fourier analysis of the de Haas--van Alphen (dHvA) oscillations in a two-dimensional (2D) electron system with background (magnetically unperturbed) reservoir states is presented. The method is exploited in a systematic study of the various wave forms of the oscillations observed in dHvA and Shubnikov--de Hass measurements on quasi-2D organic metals. It is found that at relatively moderate background strengths both the first and the second harmonics exhibit qualitative deviations from the well known Lifshitz-Kosevich-Shoenberg formula. In particular, it is found that by varying the temperature (or the magnetic field) at certain strengths of the background reservoir, the wave form can be changed from leftward to rightward asymmetry (while the second harmonic changes sign).

Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors

We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation in the vortex state of type-II superconductors, with a special focus on the connection between the gap anisotropy and the oscillation damping. Numerical calculations for three different gap structures clearly indicate that the average gap along extremal orbits is relevant for the magnitude of the extra damping, thereby providing a support for experimental efforts to probe gap anisotropy through the dHvA signal. We also derive an analytic formula for the extra damping which gives a good fit to the numerical results.

Magnetic and Fermi Surface Properties of UFeGa5

We succeeded in growing a high-quality single crystal of UFeGa 5 by the self-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and de Haas-van Alphen (dHvA) oscillation. Many dHvA branches were observed, ranging from 5.4×10 5 to 1.4×10 8 Oe. These branches are in good agreement with theoretical ones based on 5 f -itinerant RLAPW band calculations. The cyclotron mass is relatively large, ranging from 2.4 to 9.9 m 0 .

The de Haas–van Alphen Oscillation in Two-Dimensional QED at Finite Temperature and Density**The project supported by National Natural Science Foundation of China

The de Haas–van Alphen oscillations in two-dimensional QED at finite temperature and density are investigated. It is shown that for a given particle density, besides the oscillation of magnetization, the chemical potential is also oscillating with the same period. Different from the earlier work (J.O. Andersen and T. Haugset, Phys. Rev. D51 (1995) 3073), the magnetization oscillations we studied have a correct nonrelativistic limit at zero temperature.

Quadrupolar Phase Diagram and Fermi Surface Properties in the Localized 5f2-Electron System UPd3

We measured the electrical resistivity, specific heat, magnetostriction, magnetization and de Haas-van Alphen (dHvA) oscillation in UPd 3 with the hexagonal structure in order to clarify the quadrupolar and magnetic properties as well as the nature of conduction electrons. The high-field magnetization measurement at 4.2 K in magnetic fields up to about 50 T reveals two-successive metamagnetic transitions at 10.2 and 17.9 T for the field along the [0001] direction, and one transition at 27.6 T along [11\bar20]. From the results of magnetization as well as the magnetostriction measurements at various temperatures, we determined the magnetic phase diagram. Phase boundaries are discussed on the basis of the crystalline electric field scheme of the 5 f 2 configuration and the quadrupolar interaction of O zx . Reflecting the localized 5 f -electrons, the conduction electrons have small cyclotron effective masses ranging from 0.24 to 3.62 m 0 , which were determined by the dHvA experiment. The dHvA data are comp...

Landau diamagnetism and magnetization of interacting disordered conductors.

We show how the orbital magnetization of an interacting diffusive electron gas can be simply related to the magnetization of the noninteracting system having the same geometry. This result is applied to the persistent current of a mesoscopic ring and to the relation between Landau diamagnetism and the interaction correction to the magnetization of diffusive systems. The field dependence of this interaction contribution can be deduced directly from the de Haas-van Alphen oscillations of the free electron gas. Known results for the free orbital magnetism of finite systems can be used to derive the interaction contribution in the diffusive regime in various geometries.