De Haas-van Alphen Amplitude Research Articles

Highly Asymmetric Nodal Semimetal in Bulk SmB6

We show that novel low temperature properties of bulk SmB_{6}, including the sudden growth of the de Haas-van Alphen (dHvA) amplitude (and heat capacity) at millikelvin temperatures and a previously unreported linear-in-temperature bulk electrical conductivity at liquid helium temperatures, signal the presence of a highly asymmetric nodal semimetal. We show that a highly asymmetric nodal semimetal is also a predicted property of the Kondo lattice model (with dispersionless f-electron levels) in the presence of Sm vacancies or other defects. We show it can result from a topological transformation of the type recently considered by Shen and Fu and eliminates the necessity of a neutral Fermi surface for explaining bulk dHvA oscillations in SmB_{6}.

High field measurements of the Condon domain phase diagram in silver

Condon domains form when the de Haas-van Alphen (dHvA) amplitude becomes large compared to the dHvA period, i.e. μ0∂M/∂B > 1, where M is the magnetization and B the induction. This equation defines the boundary between the homogeneous magnetization and the Condon domain state. The phase diagram in the (B, T) plane can be predicted using the Lifshitz-Kosevich formula. We present the Condon domain phase diagram for a silver single crystal measured in magnetic fields up to 28 T and temperatures Tdown to 1.3 K. A standard ac method with a pickup coil system is used at low frequency for the measurements of the de Haasvan Alphen (dHvA) e..ect. The transition point from the state of homogeneous magnetization to the inhomogeneous Condon domain state is found as the point where a small irreversibility in the dHvA magnetization arises, as manifested by an extremely nonlinear response in the pickup voltage showing threshold character. The experimental results are in good agreement with theoretical predictions based on the Lifshitz-Kosevich formula.

Anomalous behavior of magneto-quantum oscillations in the organic superconductor κ-(BEDT-TTF)2I3

κ-(BEDT-TTF)2I3 is an extreme case of an electronically two-dimensional (2D) organic metal with a superconducting transition at around 4 K. In magnetic fields up to 27 T the field, angular and the temperature dependence of de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillation amplitudes were investigated. From the temperature dependence of the oscillation amplitudes the cyclotron effective massm* was investigated using Lifshitz-Kosevich formula (LK) and the surprising result is, thatm* appears to be magnetic field dependent as soon as the magnetic field is applied exactly perpendicular to the conducting planes so that the cyclotron orbit lies within those planes (i.e. Θ=0o) but field independent at Θ≠0o. It is shown that the LK formula can satisfactorily be used for the interpretation of all data obtained at Θ≠0o but not in the case where Θ=0o. An explanation of the anomalous data at Θ=0o can furthermore neither be given satisfactorily by the descriptions of magneto-quantum oscillations in 2D electronic systems nor by the occurrence of magnetic interaction effects (MI). Tentatively, the observed smaller oscillation amplitudes in κ-(BEDT-TTF)2I3 at Θ=0o above 12 T and below 1 K compared to the standard LK theory will be discussed in terms of a loss in the number of fermions by the occurrence of quasiparticles with fractional statistics.

Metamagnetic Transition in PrCu2Studied by the de Haas-van Alphen Effect

We have observed a metamagnetic transition in PrCu 2 where a cooperative Jahn-Teller effect occurs below 8 K. This transition brings about a conversion between an easy and a hard axes in magnetization, which is reflected in a drastic change of the de Haas-van Alphen amplitude, that is a change of the scattering lifetime of conduction electrons. The origin of the metamagnetic transition is ascribed to a quadrupole moment of the 4 f level.

De Haas-van Alphen studies of rare earth compounds

Abstract The de Haas-van Alphen amplitude of branch d in CeIn3 is reduced with oscillation by three orders of magnitude when the field is tilted from 〈100〉 to 〈110〉 in the {100} plane. This is explained by considering the angular dependence of the cyclotron mass and the electron spin g-factor.

High field magnetization measurements on α-(BEDTTTF) 2KHg(SCN) 4

We report torque measurements of the steady and oscillatory magnetization of α-(BEDTTTF) 2KHg(SCN) 4, where BEDTTTF is bis(ethylenedithio)tetrathiafulvalene, at temperatures down to 0.4 K in magnetic fields around at the magnetic phase transition at 24 T, the so called kink transition. The effective cyclotron mass changes only slightly at the kink transition being m ∗= m m e =1.77 ( m e is the free electron mass) above 24 T and m ∗–1.7 at 20 T for a magnetic field perpendicular to the highly conducting ac plane ( Θ=0°). For Θ=60.2° we find m ∗=3.55 (B – 18 T ). In the low field state the amplitude of the oscillatory magnetization ( μ 0 M osc=7.5 × 10 −7 T) is small; this corresponds with a high Dingle temperature (3–4 K). At 24 T a strong increase in the oscillation amplitude appears accompanied by a decrease in the Dingle temperature to T D ⩽ 2 K. The steady torque shows a quadratic increase with field at low B-values and tends to saturate near the phase transition for small angles Θ. For tilt angles Θ⩾60° the typical increase of the de Haas-van Alphen amplitude at the kink transition is no longer observed, but several anomalies occur in the steady torque above 15 T; even at 27 T α-(BEDTTTF) 2KHg(SCN) 4 is in a complex magnetic groundstate.

Some aspects of singular interactions in condensed Fermi systems

This article gives a fairly detailed survey of some of the problems raised when the interaction energy If() between 2 fermionic quasiparticles (in 2 dimensions) is singular when (k k'( - 0. Before dealing with singular interactions, it is shown how a ~ f(() leads to a 2-dimensional Fermi liquid theory, which is internally consistent, at least as far ailts infrared properties are concerned. The quasiparticle properties are calculated in detail. The question of whether singular interactions arise for the dilute Fermi gas, with short~range repulsive interactions, is investigated perturbatively. One finds a weak singularity in f(() when the dimensionality D = 2, but it does not destabilize the Fermi liquid. A more sophisticated analysis is then given, to all orders in the interaction, using the Lippman-Schwinger equation as well as a phase shift analysis for a finite box. The conclusion is that any breakdown of Fermi liquid theory must come from non-perturbative effects. An examination is then made of some of the consequences arising if a singular interaction is introduced the form proposed by Anderson is used as an example. A hierarchy of singular terms arise in all quantities this is shown for the selLenergy, and also the 3-point and 4-point scattering functions. These may be summed in a perfectly consistent manner. Most attention is given to the particle~hole channel, since it appears to lead to results different from those of Anderson. Nevertheless it appears that it is possible to derive a sensible theory starting from a singular effective Hamiltonian although Fermi Liquid theory breaks down, all fermionic quantities may be calculated consistently. Finally, the effect of a magnetic field (which cuts off the infrared divergences) is investigated, and the de Haas-van Alphen amplitude calculated, for such a singular Fermionic system.

Comment on 'de Haas-van Alphen amplitudes in heavy-electron compounds'

In a recent Letter to the Editor, Thalmeier (1987) calculates the amplitude of the de Haas-van Alphen effect to be expected in heavy-electron compounds. The authors argue that the result is in error and arises from a confusion over the relationship between the resistivity and the self-energy appropriate for a description of de Haas-van Alphen amplitudes.

Reply to Comment on 'de Haas-van Alphen amplitudes in heavy-electron compounds'

Reply to Comment on 'de Haas-van Alphen amplitudes in heavy-electron compounds'

Comment on 'de Haas-van Alphen amplitudes in heavy-electron compounds'

This Comment points out that a recent Letter to the Editor by Thalmeier is in total disagreement with present experimental results. This disagreement arises because the theory he uses is invalid; the correct theory is given in a previous publication by Stamp (1987) under the assumption that one is dealing with a Fermi liquid.

De Haas-van Alphen amplitudes in heavy-electron compounds

In heavy-electron compounds the scattering of quasi-particles increases strongly with temperature and electron energies due to many-body effects. This should lead to a deviation of the field and temperature dependence of DHVA amplitudes from the Lifshitz-Kosevich formula. Explicit expressions which can be tested experimentally are given.

De Haas-van Alphen effect in dislocated metals. I. General theoretical considerations

General results from dephasing theory for the reduction of the de Haas-van Alphen amplitude in dislocated metals are used to obtain explicit formulae valid for dislocations which are statistically independent. Though real dislocation arrays may not satisfy this condition, it is argued that in many cases they may be modelled quite well by suitable arrays of statistically independent so called pseudo-dislocations, whose stress/strain fields are those of long, straight dislocations up to a certain cut-off distance rho c from each pseudo-dislocation and are zero beyond this distance. Applications of the explicit formulae and the pseudo-dislocation model will be explored in following papers.

Departures from quasiparticle behaviour in the de Haas-van Alphen effect

Abstract An approximate expression for departures from quasiparticle behaviour of de Haas-van Alphen amplitudes is obtained. The result involves a single parameter that is independent of temperature and field and which describes a feature of the electron-phonon interaction. A value for the parameter is obtained for the β-orbit in mercury.

Precision measurements of cyclotron masses and Fermi velocities in the noble metals by the de Haas-van Alphen effect

A total of 54 cyclotron masses have been determined with great precision from the temperature dependence of the de Haas-van Alphen (dHvA) amplitudes in the noble metals Cu, Ag, and Au. The accuracy of the data is \ifmmode\pm\else\textpm\fi{}0.3%. Special care was given to the temperature and amplitude measurements. In particular the influence of magnetic interaction and of the incomplete penetration of the modulation field into the high-purity samples, which were among the most serious sources of systematic errors, were eliminated. The mass data were deconvoluted to get values of the electron velocities ${v}^{*}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ for each point on the Fermi surfaces. The qualitative behavior of ${v}^{*}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$ agrees with that found in previous works, but the absolute values differ by as much as 10%. Local values of the electron-phonon enhancement factor, $1+\ensuremath{\lambda}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}})$, were obtained in Cu by comparing velocities deduced from dHvA cyclotron masses which include electron-phonon renormalization with band velocities deduced from a band-structure calculation. Cyclotron masses were calculated for about 40 orbits not measured in each of the three metals. The coefficient of electronic specific heat was calculated from the experimental data. The agreement with the data obtained from specific-heat measurements is excellent.

Effect of alloying on the Fermi surface of magnesium. I. Experimental results for Li and In

The results of a de Haas-van Alphen study of the changes in the Mg Fermi surface in dilute MgLi and MgIn alloys are presented. The smaller Fermi-surface cross sections are studied by modulation techniques in fields up to 60 kG and by torque methods in fields up to 36 kG. Scattering temperatures were obtained for several cross sections in each alloy with typical values of 9\ifmmode^\circ\else\textdegree\fi{}K per at.% Li and 21\ifmmode^\circ\else\textdegree\fi{}K per at.% In. A method of correcting for inhomogeneities in sample concentration involving self-consistent analysis of de Haas-van Alphen amplitudes and frequencies is presented and illustrated for the highest-concentration MgLi alloy. The relative contributions of magnetic breakdown to cigar and trifoliate orbits are discussed.

De Haas-van Alphen effect in alkali metal dispersions and the Fermi surface of lithium

Measurements of the de Haas-van Alphen effect in polycrystalline dispersions of metallic lithium are described. X-ray studies indicate that the low-temperature martensitic transformation is suppressed in samples of this form, and that the room temperature BCC structure is retained down to liquid helium temperatures. The de Haas-van Alphen amplitude shows a characteristic beat structure arising from the Fermi surface anisotropy. The radial distortion of the BCC Fermi surface is estimated to be 2.6+or-0.9%. The method of analysis is verified by similar measurements in dispersion of sodium. The results for lithium are consistent with the most recent positron annihilation, Compton scattering and optical absorption data, but yield a Fermi surface distortion which is significantly less than that given by typical bandstructure calculations. This discrepancy lends support to the suggestion of Rasolt, Nickerson and Vosko that non-local exchange and correlation effects may cause a substantial reduction of the Fermi surface anisotropy (see Solid State Commun., vol.16, p.827 (1975)).

The apparent Dingle temperature in Zn?Mn, Zn?Cr, and Zn?Fe

The apparent Dingle temperature of the 3rd zone needles in several alloys of Zn−Mn, Zn−Cr and Zn−Fe has been determined from the absolute amplitude of the de Haas-van Alphen effect over the temperature range 1.6 K to 4.2 K and the field range 0 to 9 kG. The results show clearly that potential scatteringnot spin scattering dominates in all three systems. In addition, a “cross-over” behaviour in the de Haas-van Alphen amplitudes results from the scattering of the magnetic moments of the impurity spin.

Validity of de Haas-van Alphen dephasing calculations

Criteria, developed in an accompanying paper (see ibid., vol.4, 1371 (1974), for the validity of dephasing calculations of the reduction of the de Haas-van Alphen amplitude, are applied to two cases: metals containing dislocations and metals containing impurities. It is found that the calculations for dislocations should be perfectly reliable, whereas those for impurities should only be capable of reasonable estimates.

Dephasing of the de Haas-van Alphen effect by impurities

Expressions for the de Haas-van Alphen amplitude reduction produced by the strain field of a random distribution of impurities are obtained, the principal purpose being to find out whether dephasing is likely to practice to reduce the amplitude comparably with scattering of electrons by the impurities.

The influence on the de Haas-van Alphen effect of impurity-induced strain

Abstract A previously unconsidered mechanism for reducing the amplitude of de Haas-van Alphen oscillations is dephasing of the signals by the strain fields that surround an impurity. This effect is calculated and the resultant amplitude and phase are found to be appreciably affected. It is shown that in some cases a major part of the total impurity scattering obtained from measurements of the de Haas-van Alphen amplitude must be attributed to strain and that considerable care should therefore be taken when interpreting such experiments. Experimental measurements of both phase and amplitude in dilute CuIn alloys, which are characterized by large strain effects, are presented and confirm many features of the theory.