Fermi surface reconstruction in chromium at high pressure and high magnetic fields

Elemental chromium is an itinerant, antiferromagnet with an incommensurate spin and charge density wave structure below 311 kelvin. The Fermi surface in this state is a direct result of the three dimensional nesting of large portions of the paramagnetic Fermi surface seen above 311 K. Due to the large amount of overlap of two of the electron and hole pockets by the spin density wave vector Q, both of these sheets are gapped and have not been resolved in previous experiments. The sheets of the Fermi surface that are not gapped can be configured by overlapping the remaining sheets through integer translations of the nesting vector, +/-nQ. This provides a complex spectra of orbits via observation of the Shubnikov-de Haas or de Haas-van Alphen effects.;Studies have been performed on chromium, via a variety of high pressure techniques, including diamond anvil and piston cylinder pressure cells, and across multiple magnet platforms. Quantum oscillations have revealed a pressure-induced Fermi surface reconstruction at PSF= 0.93 GPa, due to the suppression of the spin flip transition. Changes were observed in the Fermi surface in the low pressure, longitudinally polarized state, and the high pressure, transversely polarized state and were clearly demonstrated in the spectrum at P= 1.47 GPa. Using the Lifshitz-Kosevich formula, which relates quantum oscillation amplitude to electron effective mass, we found a reduction of many-body correlations by a factor of ∼ 5, above PSF. A high field transition was also observed that showed the field induced reorientation of one component of the spin density wave vector at fields ∼ 40 T. Orientation of the spin density wave vector by cooling through the AFM transition had been seen before, but no work on zero-field cooled samples has been reported previously. This work presents details of the low temperature ground state of AFM chromium, for which both the spin flip transition and the AFM Fermi surface have incomplete theoretical formulations. The understanding and knowledge of the mechanism in chromium for quantum interference oscillations, proposed in early experiments specific to two orbits, was expanded to several orbits in the low frequency FFT spectrum and the relationship of those orbits to well established Landau quantization orbits of similar frequencies was also provided.