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In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators.…
We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB$_{12}$ and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary…
Within condensed-matter systems, strong electronic interactions often lead to exotic quantum phases. A recent manifestation of this is the unexpected observation of magnetic quantum oscillations and metallic thermal transport, both…
Insulators occur in more than one guise, a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here we report the observation of an unusual insulating state with an…
The observation of quantum oscillations in topological Kondo insulators SmB6 and YbB12 is a recent puzzling experimental discovery. Quantum oscillations observed in the resistivity and the magnetization are usually explained by the…
A highly exotic phenomenon in solid-state physics is the observation of magnetic quantum oscillations in insulators. For instance, in the Kondo insulator YbB$_{12}$ various groups reported the observation of such oscillations seemingly…
Quantum oscillations (QOs) in transport and thermodynamic parameters at high magnetic fields are an unambiguous signature of the Fermi surface, the defining characteristic of a metal. Therefore, recent observations of QOs in insulating…
The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator-metal transition, where theory…
The observation of $1/B$-periodic behavior in Kondo insulators SmB$_6$ and YbB$_{12}$ challenges the conventional wisdom that quantum oscillations (QO) necessarily arise from Fermi surfaces in metals. We revisit recently proposed theories…
The finding of bulk quantum oscillations in the bulk Kondo insulator SmB$_6$, which has been proposed to be a correlated topological insulator, proved a considerable surprise. The subsequent measurement of bulk quantum oscillations in other…
In correlated electronic systems, strong interactions and the interplay between different degrees of freedom may give rise to anomalous charge transport properties, which can be tuned by external parameters like temperature and magnetic…
Defying the traditional classification into metals and insulators, several materials simultaneously display metallic thermal properties and insulating electric behaviour, as if they hosted quasiparticles carrying entropy but not charge.…
Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by…
Materials where localized magnetic moments are coupled to itinerant electrons, the so-called Kondo lattice materials, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, including…
The phase landscape of UTe$_2$ features a remarkable diversity of superconducting phases under applied pressure and magnetic field. Recent quantum oscillation studies at ambient pressure have revealed the quasi-2D Fermi surface of this…
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…
Despite the fact that 1111-type iron arsenides hold the record transition temperature of iron-based superconductors, their electronic structures have not been studied much because of the lack of high-quality single crystals. In this study,…
In heavy fermions the relaxation dynamics of photoexcited carriers has been found to be governed by the low energy indirect gap, E$_{g}$, resulting from hybridization between localized moments and conduction band electrons. Here, carrier…
Intermetallic compounds containing $f$-electron elements have been prototypical materials for investigating strong electron correlations and quantum criticality (QC). Their heavy fermion ground state evoked by the magnetic $f$-electrons is…
$\alpha$-YbAlB$_4$ is the locally isostructural polymorph of $\beta$-YbAlB$_4$, the first example of an Yb-based heavy fermion superconductor which exhibits pronounced non-Fermi-liquid behavior above $T_{\rm c}$. Interestingly, both…