High magnetic fields have proven instrumental in exploring the physical properties of condensed matter, leading to groundbreaking discoveries such as the quantum Hall effect in 2D heterostructures and quantum oscillations in cuprate superconductors. The ability to conduct precise measurements at progressively higher magnetic fields continues to push the frontiers of knowledge and enable new discoveries. In this work, we present the development of a microwave technique for performing two-point transport measurements in semi-destructive pulsed magnetic fields (up to 125 T) and at low temperatures (down to 1.5 K) with unprecedented sensitivity. This new setup was tested on a variety of samples. We present results on the metal-insulator transition in InAs and we report notably the first observation of Shubnikov-de-Haas oscillations in WTe_2 at magnetic fields beyond 100 T.

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Magnetoresistivity ρ(xx) and Hall resistivity ρ(xy) in ultrahigh magnetic fields up to 88 T are measured down to 0.15 K to clarify the multiband electronic structure in high-quality single crystals of superconducting FeSe. At low temperatures and high fields we observe quantum oscillations in both resistivity and the Hall effect, confirming the multiband Fermi surface with small volumes. We propose a novel approach to identify from magnetotransport measurements the sign of the charge carriers corresponding to a particular cyclotron orbit in a compensated metal. The observed significant differences in the relative amplitudes of the quantum oscillations between the ρ(xx) and ρ(xy) components, together with the positive sign of the high-field ρ(xy), reveal that the largest pocket should correspond to the hole band. The low-field magnetotransport data in the normal state suggest that, in addition to one hole and one almost compensated electron band, the orthorhombic phase of FeSe exhibits an additional tiny electron pocket with a high mobility.

Received 5 November 2015DOI:https://doi.org/10.1103/PhysRevLett.115.219902© 2015 American Physical Society

The use of brain scanning now dominates the cognitive sciences, but important questions remain to be answered about what, exactly, scanning can tell us. One corner of cognitive science that has been transformed by the use of neuroimaging, and that a scanning enthusiast might point to as proof of scanning's importance, is the study of face perception. Against this view, we argue that the use of scanning has, in fact, told us rather little about the information processing underlying face perception and that it is not likely to tell us much more.

The temperature dependence of the magnetic susceptibility and Mössbauer spectra of the compounds FeL2[Ni(CN)4] (L=2, 3 or 4-methylpyridine) have been investigated. In each case the iron(II) ions are high spin at room temperature, but in the 3-methylpyridine compound about half of the iron ions becomes diamagnetic around 90K. The application of external pressure allowed to uncover the underlying two-step nature of this spin transition. For further increase of the pressure the plateau between the two steps disappeared. Both observations were successfully interpreted in the framework of an Ising-like model with two iron sites displaying different volume changes.