Quantum Oscillation Studies Research Articles

Role offElectrons in the Fermi Surface of the Heavy Fermion Superconductorβ−YbAlB4

We present a detailed quantum oscillation study of the Fermi surface of the recently discovered Yb-based heavy fermion superconductor beta-YbAlB4. We compare the data, obtained at fields from 10 to 45 T, to band structure calculations performed using the local density approximation. Analysis of the data suggests that f holes participate in the Fermi surface up to the highest magnetic fields studied. We comment on the significance of these findings for the unconventional superconducting properties of this material.

Quantum oscillation studies of the Fermi surface of LaFePO

We review recent experimental measurements of the Fermi surface of the iron–pnictide superconductor LaFePO using quantum oscillation techniques. These studies show that the Fermi surface topology is close to that predicted by first principles density functional theory calculations, consisting of quasi-two-dimensional electron-like and hole-like sheets. The total volume of the two hole sheets is almost equal to that of the two electron sheets, and the hole and electron Fermi surface sheets are close to a nesting condition. No evidence for the predicted three-dimensional pocket arising from the Fe d z 2 band is found. Measurements of the effective mass suggest a renormalisation of around two, close to the value for the overall band renormalisation found in recent angle resolved photoemission measurements.

Oscilação quântica de sabores com pacotes de ondas

Sugerimos um esquema de aproximação analítica para estudarmos os fenômenos de oscilação de quântica de sabores de uma maneira pedagógica e compreensiva. Após uma breve descrição do status em que se encontra o estudo teórico dos fenômenos de oscilação, com uma discussão introdutória dos resultados obtidos com ondas planas, nós introduzimos o formalismo com pacotes de ondas de modo a estudar algumas características peculiares inerentes aos fenômenos de oscilação quântica. Seguimos um estudo analítico com um pacote de ondas Gaussiano onde mostramos que as oscilações são limitadas por uma função amortizada ao longo do tempo a qual caracteriza o slippage (''escorregamento'') entre dois pacotes de ondas. Demonstramos que o spreading de um pacote de ondas é tipicamente um efeito de segunda ordem, de fato, relevante no limite não-relativístico. Ao mesmo tempo, quantificamos uma fase adicional dependente do tempo a qual modifica o caráter standard de oscilação da fórmula de conversão de sabores. Finalmente, consideramos uma função Quadrada e uma função Seno para descrevermos a localização das partículas e verificamos como se altera a probabilidade de oscilação de sabores sob tais circunstâncias.

THE DE HAAS-VAN ALPHEN EFFECT IN CeMIn5 (Where M = Rh and Co)

To understand the electronic structure of the heavy fermion superconductors CeMIn 5, we have performed a comprehensive magnetic study of these materials.1-4 Our quantum oscillation studies reveal that the Fermi surface becomes systematically more 2-d (and displays heavier effective masses) as one progresses from M=Rh to M=Ir to M=Co, consistent with the observed increase in superconducting Tc. Furthermore, dilution studies show that the f-electrons in CeRhIn5 are substantially localized whereas in CeIrIn 5 and CeCoIn 5 a more itinerant character is observed.

Magnetism and fermiology ofκ-(BEDT-TSF)2FeCl4

Magnetization studies reveal that the ground state of {kappa}-(BEDT-TSF){sub 2}FeCl{sub 4} is J = 1/2 with weak antiferromagnetic correlations. Quantum oscillation studies indicate that the effective masses of the quasiparticles are considerably enhanced with respect to those of isostructural {kappa}-(BEDT-TSF){sub 2}GaCl{sub 4}. We attribute the mass enhancement to spin fluctuation effects involving the Fe magnetic moments within the inorganic layer. {copyright} {ital 1998} {ital The American Physical Society}

Magnetic quantum oscillations in Ce-based heavy-fermion compounds

We report on quantum oscillation studies in Ce-based heavy-fermion compounds, in particular on the magnetic field dependence of the quasiparticle effective mass in CeB 6 at the lowest possible fields. We make use of a new SQUID-based de Haas-van Alphen (dHvA) spectrometer, which was developed for use in very high magnetic fields (upto 19 T) and at ultralow temperatures (<3 mK) for the study of heavy-fermion materials. As a result of the unprecedented sensitivity, the dHvA measurements have been extended to much lower magnetic field regimes and temperatures than previously possible.

Calculation of thermodynamic and transport properties of Sr 2RuO 4 at low temperatures using known fermi surface parameters

We report the results of a study of quantum oscillations in the layered perovskite superconductor Sr 2RuO 4. All three predicted sheets of the Fermi surface have been observed, and we show how the measured Fermi surface parameters and quasiparticle cyclotron masses can be used to make successful quantitative predictions of a number of physical properties that can be measured independently.

A cryomagnetic system achieving 17T and &lt;3mK

The design and performance of a cryomagnetic facility capable of achieving a temperature of 3mK in a magnetic field of 17T is presented. Using adiabatic nuclear demagnetisation of a copper stage, a3He melting curve thermometer may be cooled to a temperature below 914μK, the spin ordering temperature of the solid3He. The lower end of a silver rod coupled to this stage and extending into a 17T magnetic field cools to below 3mK, where the nuclear heat capacity of the silver is rising. The careful design of the vibration isolation of the cryostat reduces the heat leak in full field to below 2nW. This cryostat is currently being used for quantum oscillation studies of the heaviest quasiparticles associated with heavy fermion systems.

Uniaxial strain derivatives of the Fermi surface of copper

From a comprehensive experimental study of quantum oscillations in magnetostriction and torque, values have been deduced for all nonvanishing tetragonal and angular shear strain derivatives for the five principal extremal cross sections of the Fermi surface of copper, viz., the neck and belly normal to [111], the dogsbone normal to [110], and the rosette and belly normal to [001]. It is found that the neck is most sensitive to angular shear strain, whereas the bellies are most affected by uniform dilation. For the other orbits the magnitudes of shear and dilation derivatives are comparable.The results are self-consistent and agree with the experimental tensile stress results of Shoenberg and Watts. Earlier magnetostriction results for the neck obtained by Aron and by Slavin can be brought into agreement with the present data by recalculating the former using the now accepted value for the neck effective mass. The present experimental derivatives are in qualitative agreement with the theoretical values calculated by Lee, except for the tetragonal shear derivative of the [001] belly, for which the theoretical value is about 50% higher than the experimental one. This discrepancy is not fully understood.

Lineshape studies of quantum oscillations in the ultrasonic absorption and dispersion in indium. The anomalous behaviour of the ultrasonic absorption

Simultaneous measurements of quantum oscillations in the ultrasonic absorption and dispersion in In and dilute In/Pb alloys have been carried out using a sensitive continuous wave technique. A comparison of the field dependences and the harmonic contents of the quantum oscillations in the absorption, dispersion and magnetisation has shown that the dispersion and magnetisation are in agreement with the existing theories. The absorption oscillations, however, do not follow the well known theories. A modified expression for the absorption lines has been derived by calculating the giant quantum oscillation lineshape in the presence of significant phase smearing. The Dingle temperatures and harmonic content calculated from this modified expression are in excellent agreement with the results obtained from the de Haas-van Alphen effect and the velocity oscillations.

Possible field dependence of Landau level-broadening

The broadening of the Landau levels in a pure metal (which leads to a Dingle temperature in the de Haas-van Alphen effect) is probably mainly due to small angle scattering of electrons by extended defects. Simple intuitive arguments suggest that the broadening (and therefore the effective Dingle temperature) should become smaller as the magnetic field is increased into the region of the quantum limit (i.e. low quantum numbers). Some experimental evidence supporting this suggestion can be found in published studies of giant quantum oscillations in ultrasonic attenuation, and further evidence will be presented based on recent experiments on the de Haas-van Alphen effect in bismuth.

Magnetostriction and Magnetoelastic Quantum Oscillations inp−PbTe

A detailed experimental and theoretical study of quantum oscillations in the magnetostriction and Young's modulus of $p\ensuremath{-}\mathrm{PbTe}$ is presented. The valence band of PbTe is approximated by a spheroidal nonparabolic model in which the effects of strain on the valence-band parameters are described by a deformation potential model. Using appropriate thermodynamic derivatives of the modified Lifshitz-Kosevich expression for the oscillatory part of the electronic free energy, it is shown that both types of oscillations arise mainly from relative shifts of the valence-band maxima due to shear strains, accompanied by intervalley charge transfer. Band parameters derived from the periods, phases, and spin splitting of the oscillations are in generally good agreement with values reported by other workers. A detailed comparison is made of the experimentally observed oscillation amplitudes with those predicted by theory, and satisfactory agreement is found. The ratio of the amplitudes of the two effects yiends a value of the valence-band deformation potential ${\ensuremath{\Xi}}_{u}^{v}=7.9\ifmmode\pm\else\textpm\fi{}1.3$ eV in good agreement with a value found from piezoresistance experiments by Burke.

Galvanomagnetic Investigation of Energy Bands in Arsenic

The isothermal magnetoresistivity and Hall resistivity in a monocrystal of arsenic have been studied at temperatures of liquid helium in fields up to 25 kG. All measurements were taken in the basal plane of the crystal with magnetic field perpendicular to the plane and parallel to the trigonal axis. The binary axis was in the basal plane and parallel to the long dimension of the crystal. The magnetoconductivity tensor element ${\ensuremath{\sigma}}_{11}$ and the Hall conductivity element ${\ensuremath{\sigma}}_{12}$ were constructed from resistivity data and analyzed in terms of two-and three-band models. A least-squares curve fitting of the conductivities to the quasiclassical model of Sondheimer and Wilson indicates two major energy bands of carriers. The Hall effect is positive. The high-mobility carriers are holes with mobility approximately four times that of the equally populous electrons. The carrier concentration is $n\ensuremath{\simeq}\frac{2\ifmmode\times\else\texttimes\fi{}{10}^{20}}{{\mathrm{cm}}^{3}}$ if determined from ${\ensuremath{\sigma}}_{11}$ data along with effective-mass anisotropy data established from quantum-oscillation studies. Simultaneous curve fitting of the ${\ensuremath{\sigma}}_{11}$ and ${\ensuremath{\sigma}}_{12}$ data gives $n\ensuremath{\simeq}\frac{0.7\ifmmode\times\else\texttimes\fi{}{10}^{20}}{{\mathrm{cm}}^{3}}$.