A new algorithm for extracting de Haas-van Alphen frequencies and effective masses from calculated band energies is presented. The algorithm creates an interpolated k-space super cell, which is broken into slices perpendicular to the desired magnetic
field direction. Fermi surface orbits are located within each slice, and de Haas-van Alphen frequencies and effective masses are calculated. Orbits are then matched across slices, and extremal orbits determined. This technique has been successful in locating extremal orbits not previously noticed in the complicated topology of existing UPt3 band-structure data; these new orbits agree with experimental de Haas-van Alphen measurements on this material, and solidify the case for a fully-itinerant model of UPt3.
Pulsed field measurements of the Hall resistivity and magnetoresistance of underdoped YBa2Cu4O8 are analyzed self-consistently using a simple model based on coexisting electron and hole carriers. The resultant mobilities and Hall numbers are found to
vary markedly with temperature. The conductivity of the hole carriers drops by one order of magnitude below 30 K, explaining the absence of quantum oscillations from these particular pockets. Meanwhile the Hall coefficient of the electron carriers becomes strongly negative below 50 K. The overall quality of the fits not only provides strong evidence for Fermi-surface reconstruction in Y-based cuprates, it also strongly constrains the type of reconstruction that might be occurring.
Magnetic-field-induced changes of the Fermi surface play a central role in theories of the exotic quantum criticality of YbRh2Si2. We have carried out de Haas-van Alphen measurements in the magnetic-field range 8 T <= H <= 16 T, and directly observe
field dependence of the extremal Fermi surface areas. Our data support the theory that a low-field large Fermi surface, including the Yb 4f quasihole, is increasingly spin split until a majority-spin branch undergoes a Lifshitz transition and disappears at H0 ~ 10 T, without requiring 4f localization at H0.
Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt3. Our work was partially motivated by a new proposal that two 5f valence electron
s per formula unit in UPt3 are localized by correlation effects -- agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this partially localized model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed fully itinerant model of the electronic structure of UPt3. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.
We present quantum oscillation measurements of YbRh2Si2 at magnetic fields above the Kondo-suppression scale H0 ~ 10 T. Comparison with electronic structure calculations is complicated because the small Fermi surface, where the Yb 4f-quasi-hole is no
t contributing to the Fermi volume, and large Fermi surface, where the Yb 4f-quasi-hole is contributing to the Fermi volume, are related by a rigid Fermi energy shift. This means that spin-split branches of the large Fermi surface can look like unsplit branches of the small surface, and vice-versa. Thus, although the high-field angle dependence of the experimentally-measured oscillation frequencies most resembles the electronic structure prediction for the small Fermi surface, this may instead be a branch of the spin-split large Fermi surface.
