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Iris Nandhakumar

Publications and source records attributed to Iris Nandhakumar.

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Fabry-Perot Interference, g-factor Anisotropy, and Gate-Tunable Quantum dot in Chiral Tellurium Nanowires

Chiral materials with strong spin-orbit coupling offer a unique platform for exploring the interplay between topology, chirality, and quantum transport yet the quantum coherent regime in elemental tellurium nanostructures remains largely unexplored. Here we demonstrate phase-coherent quasi-ballistic transport, anisotropic Zeeman spectroscopy, and gate-tunable quantum dot formation in hydrothermally grown t-tellurium nanowires. Single nanowire field-effect transistors exhibit p-type transport with hole mobilities rising from approx. 80 cm2 V-1 s-1 at 210 K to approx. 190 cm2 V-1 s-1 at 1 K, consistent with a crossover from phonon-limited to Coulomb scattering dominated regimes near 50 K. Notably, devices segregate into two distinct regimes based on their room temperature two-terminal resistance : low-resistance devices (< 30 kOhm) exhibit Fabry-Perot interference, whereas high resistance devices (> 30 kOhm) display Coulomb-blockade behavior revealing a two-terminal resistance-driven transition between quasi-ballistic and strongly localized transport regimes. Zeeman spectroscopy in in-plane and out-of-plane magnetic fields yields highly anisotropic Lande g-factors (an in-plane gparallel = 1.18 and an out-of-plane gperp = 18.41) and directly resolves a spin-orbit energy gap DeltaSO = 0.864 meV from an avoided crossing. These results establish chiral tellurium nanowires as a versatile platform for gate-defined spin qubits exploiting large, tunable g-factors and for hybrid tellurium-superconductor architectures targeting Majorana zero modes in an elemental vdW system.

cond-mat.mes-hall

Electronic transport descriptors for the rapid screening of thermoelectric materials

The discovery of novel materials for thermoelectric energy conversion has potential to be accelerated by data-driven screening combined with high-throughput calculations. One way to increase the efficacy of successfully choosing a candidate material is through its evaluation using transport descriptors. Using a data-driven screening, we selected 12 potential candidates in the trigonal ABX2 family, followed by charge transport property simulations from first principles. The results suggest that carrier scattering processes in these materials are dominated by ionised impurities and polar optical phonons, contrary to the oft-assumed acoustic-phonon-dominated scattering. Combined with calculations of thermal conductivity based on three-phonon scattering, we predict p-type AgBiS2 and TlBiTe2 as potential high-performance thermoelectrics in the intermediate temperature range for low grade waste heat harvesting, with a predicted zT above 1 at 500 K. Using these data, we further derive ground-state transport descriptors for the carrier mobility and the thermoelectric power factor. In addition to low carrier mass, high dielectric constant was found to be an important factor towards high carrier mobility. A quadratic correlation between dielectric constant and transport performance was established and further validated with literature. Looking ahead, dielectric constant can potentially be exploited as an independent tuning knob for improving the thermoelectric performance.

cond-mat.mtrl-sci