The topological properties of fermions arise from their low-energy Dirac-like band dispersion and associated chiralities. Initially confined to points, extensions of the Dirac dispersion to lines and even loops have now been uncovered and semimetals hosting such features have been identified. However, experimental evidence for the enhanced correlation effects predicted to occur in these topological semimetals has been lacking. Here, we report a quantum oscillation study of the nodal loop semimetal ZrSiS in high magnetic fields that reveals significant enhancement in the effective mass of the quasiparticles residing near the nodal loop. Above a threshold field, magnetic breakdown occurs across gaps in the loop structure with orbits that enclose different windings around its vertices, each winding accompanied by an additional π Berry phase. The amplitudes of these breakdown orbits exhibit an anomalous temperature dependence. These findings demonstrate the emergence of novel, correlation-driven physics in ZrSiS associated with the Dirac-like quasiparticles.

The diameter dependence of the thermal conductivity of InAs nanowires in the range of 40-1500 nm has been measured. We demonstrate a reduction in thermal conductivity of 80% for 40 nm nanowires, opening the way for further design strategies for nanoscaled thermoelectric materials. Furthermore, we investigate the effect of thermal contact in the most common measurement method for nanoscale thermal conductivity. Our study allows for the determination of the thermal contact using existing measurement setups. The thermal contact resistance is found to be comparable to the wire thermal resistance for wires with a diameter of 90 nm and higher.

We report a study of quantum oscillations in the high-field magneto-resistance of the nodal-line semimetal HfSiS. In the presence of a magnetic field up to 31 T parallel to the c-axis, we observe quantum oscillations originating both from orbits of individual electron and hole pockets, and from magnetic breakdown between these pockets. In particular, we find an oscillation associated with a breakdown orbit enclosing one electron and one hole pocket in the form of a 'figure of eight'. This observation represents an experimental confirmation of the momentum space analog of Klein tunneling. When the c-axis and the magnetic field are misaligned with respect to one another, this oscillation rapidly decreases in intensity. Finally, we extract the cyclotron masses from the temperature dependence of the oscillations, and find that the mass of the 'figure of eight' orbit corresponds to the sum of the individual pockets, consistent with theoretical predictions for Klein tunneling in topological semimetals.

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momentum directions. In the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry, Dirac semimetals evolve into Weyl semimetals and Dirac points split into pairs of Weyl points due to the lifted spin degeneracy. [8,9] For both the Dirac and Weyl semimetals, due to the coexistence of the conventional charge carriers and relativistic carriers, interesting transport phenomena can often be observed, for example, chiral anomaly [10][11][12] and ultrahigh carrier mobilities. [13] Accordingly, transport studies are viewed as an important way to explore the unique scattering mechanism of charge carriers in Dirac/Weyl semimetals. In addition, through transport quantum oscillations, one can get deep insights into the underlying band topology of Dirac/Weyl semimetals.In general, Weyl semimetals can be classified into two types: the standard type I which possesses a point-like Fermi surface, and the type II with strongly tilted Weyl cones induced by the broken Lorentz symmetry. [14] The Weyl points for type II Weyl semimetals appear only at the contact of electron and hole pockets. The qualitatively distinct band topology of type II Weyl semimetals can lead to marked differences in physical properties, such as the direction restricted chiral anomaly and exotic superconductivity. [15][16][17] To date, several noncentrosymmetric material systems, for example, the transition metal dichalcogenides T M X 2 (T M = W, Mo, etc.; X = Se, Te), [14,[18][19][20] the diphosphides (Mo, W)P 2 , [21] LaAlGe, [22] etc., have been considered to be type II Weyl semimetals, while most of them display complex band structures with multiple Weyl points, which adds difficulties in the conventional transport studies of these materials. Moreover, in many Weyl semimetals, the Weyl points are located deeply below the Fermi level, which often hinders the observation of intrinsic characteristics associated with the relativistic carriers.Very recently, ternary MTTe 4 (M = Nb or Ta; T = Ir or Rh) compounds were theoretically predicted as a new series of type II Weyl semimetals, [23,24] and verified experimentally in TaIrTe 4 . [25][26][27] In comparison with the previous type II Weyl semimetals, the angle-resolved photoemission spectroscopy (ARPES) data and band calculation of TaIrTe 4 suggests the existence of only four Weyl points, [24,26] which is the minimum number of Weyl points allowed for a time-reversal invariant Weyl semimetals, characterized by nodal points in the bulk and Fermi arc states on the surface, have recently attracted extensive attention due to their potential application as materials for low-energy-consumption electronics. The thermodynamic and transport properties of a theoretically predicted Weyl semimetal NbIrTe 4 is measured in high magnetic fields up to 35 T and low temperatures down to 0.4 K. Remarkably, NbIrTe 4 exhibits a nonsaturating transverse magnetoresistance that follows a power-law dependence in B. Low-field Hall measurements reveal that hole-like carriers dominate the transport for T > 80 K, while...