Robert Kealhofer

Magnetic torque anomaly in the quantum limit of Weyl semimetals

Electrons in materials with linear dispersion behave as massless Weyl- or Dirac-quasiparticles, and continue to intrigue due to their close resemblance to elusive ultra-relativistic particles as well as their potential for future electronics. Yet the experimental signatures of Weyl-fermions are often subtle and indirect, in particular if they coexist with conventional, massive quasiparticles. Here we show a pronounced anomaly in the magnetic torque of the Weyl semimetal NbAs upon entering the quantum limit state in high magnetic fields. The torque changes sign in the quantum limit, signalling a reversal of the magnetic anisotropy that can be directly attributed to the topological nature of the Weyl electrons. Our results establish that anomalous quantum limit torque measurements provide a direct experimental method to identify and distinguish Weyl and Dirac systems.

Observation of a two-dimensional Fermi surface and Dirac dispersion in YbMnSb2

We present the crystal structure, electronic structure, and transport properties of the material

Black Arsenic: A Layered Semiconductor with Extreme In‐Plane Anisotropy

{\mathrm{YbMnSb}}_{2}

Thermodynamic anomaly above the superconducting critical temperature in the quasi-one-dimensional superconductor Ta4Pd3Te16

, a candidate system for the investigation of Dirac physics in the presence of magnetic order. Our measurements reveal that this system is a low-carrier-density semimetal with a two-dimensional Fermi surface arising from a Dirac dispersion, consistent with the predictions of density-functional-theory calculations of the antiferromagnetic system. The low temperature resistivity is very large, suggesting that scattering in this system is highly efficient at dissipating momentum despite its Dirac-like nature.

Direct visualization of coexisting channels of interaction in CeSb

2D layered materials have emerged in recent years as a new platform to host novel electronic, optical, or excitonic physics and develop unprecedented nanoelectronic and energy applications. By definition, these materials are strongly anisotropic between the basal plane and cross the plane. The structural and property anisotropies inside their basal plane, however, are much less investigated. Black phosphorus, for example, is a 2D material that has such in-plane anisotropy. Here, a rare chemical form of arsenic, called black-arsenic (b-As), is reported as a cousin of black phosphorus, as an extremely anisotropic layered semiconductor. Systematic characterization of the structural, electronic, thermal, and electrical properties of b-As single crystals is performed, with particular focus on its anisotropies along two in-plane principle axes, armchair (AC) and zigzag (ZZ). The analysis shows that b-As exhibits higher or comparable electronic, thermal, and electric transport anisotropies between the AC and ZZ directions than any other known 2D crystals. Such extreme in-plane anisotropies can potentially implement novel ideas for scientific research and device applications.

Electronic devices of thin crystals of sodium iridate

We study the intrinsic transport anisotropy and fermiology of the quasi one-dimensional superconductor Ta

Electronic transport in thin crystals of ruthenium chloride

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2D Magnetic Order in Ru Doped Honeycomb Material, FePS3

Pd

Observation of two-dimensional Fermi surface and Dirac dispersion in the new material YbMnSb

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Te