arXiv subjects

Teresa Kulka

Publications and source records attributed to Teresa Kulka.

4 recordsLinked to original sources

arXiv2026

Taming quantum interference: a route to high electrical conductance in carbon nanotube assemblies

In nanostructured networks, transport is governed by junctions between neighbouring building blocks. Improving their alignment and removing defects is the intuitive route to better electron transport. At low temperatures, when transport becomes coherent, a junction cannot always be reduced to a single effective resistance, because electron-wave interference can strongly enhance or suppress transmission even in nominally ideal junctions. Using carbon nanotube (CNT) networks as a model system, we explore coherent transport through experimentally relevant junctions, from single and multiple single-walled CNT (SWCNT) contacts to double-walled CNT (DWCNT) and multi-walled CNT (MWCNT) junctions, with atomistic tight-binding non-equilibrium Green's-function calculations, also under a perpendicular magnetic field. We use analytically solvable minimal models to identify transport regimes expected for quasi-1D nanoscale junctions, and an electron-waveguide picture to interpret their CNT-specific manifestations. For single SWCNT--SWCNT junctions, high-transmission windows are set mainly by overlap length, doping and magnetic field. Gateway states can enhance conductance when some CNT subbands are gapped, and in some cases a magnetic field can restore transmission by lifting an interference blockade. In more complex architectures, added paths become selective: multi-junctions generate resonant filtering, while additional walls redistribute transmission instead of acting as independent channels. DWCNT junctions remain outer-wall dominated and SWCNT-like, whereas MWCNT junctions redistribute transmission among coupled walls and show a more complex field response. Our ultrahigh-field measurements likewise show lower, more field-sensitive conductance in MWCNT than SWCNT fibres. This work turns microscopic interference mechanisms into design principles for high-conductance, field-stable CNT conductors.

cond-mat.mes-hall↗

arXiv2026

Quantum Limits of Electronic Transport in Nanostructured Macroscopic Conductors

Macroscopic assemblies of one- and two-dimensional materials promise to translate nanoscale electronic properties into device-scale performance, yet the microscopic principles governing charge transport in such networks remain unresolved. In these systems, conductivity is often interpreted using phenomenological models that do not explicitly connect electronic structure to macroscopic magnetotransport. Here we develop a unified atomistic framework that links quantum-coherent transport, thermal disorder and magnetic-field effects, and combine it with ultrahigh-field magnetotransport measurements up to 60 T over a broad temperature range on carbon nanotube fibres. We show that positive magnetoresistance is controlled by junction overlap length, whereas negative magnetoresistance arises predominantly from lattice-mismatched heterojunctions rather than weak localisation alone. Statistical analysis of a large-scale numerical dataset reveals that the experimentally observed positive quadratic magnetoresistance originates from junction transport. These results show that macroscopic transport in disordered low-dimensional networks is governed primarily by junction-level quantum interference rather than solely by defects or doping.

cond-mat.mtrl-sci↗

arXiv2025

Adjudicating Conduction Mechanisms in High Performance Carbon Nanotube Fibers

The performance of carbon nanotube (CNT) cables, a contender for copper-wire replacement, is tied to its metallic and semi-conducting-like conductivity responses with temperature; the origin of the semi-conducting-like response however is an underappreciated incongruity in literature. With controlled aspect-ratio and doping-degree, over 61 unique cryogenic experiments including anisotropy and Hall measurements, CNT cable performance is explored at extreme temperatures (65 mK) and magnetic fields (60 T). A semi-conducting-like conductivity response with temperature becomes temperature-independent approaching absolute-zero, uniquely demonstrating the necessity of heterogeneous fluctuation induced tunneling; complete de-doping leads to localized hopping, contrasting graphite's pure metallic-like response. High-field magneto-resistance (including +22% longitudinal magneto-resistance near room-temperature) is analyzed with hopping and classical two-band models, both similarly yielding a parameter useful for conductor development. Varying field-orientation angle uncovers two-and four-fold symmetries from Aharonov-Bohm-like corrections to curvature-induced bandgap. Tight-binding calculations using Green's Function formalism model large-scale, coherent transport in commensurate CNT bundles in magnetic field, revealing non-uniform transmission across bundle cross-sections with doping restoring uniformity; independent of doping, transport in bundle-junction-bundle systems are predominantly from CNTs adjacent to the other bundle. The final impact is predicting the ultimate conductivity of heterogeneous CNT cables using temperature and field-dependent transport, surpassing conductivity of traditional metals.

cond-mat.mtrl-sci↗

arXiv2025

Nature of Spinons in 1D Spin Chains

We provide an intuitive understanding of the collective low-energy spin excitation of the one-dimensional spin-1/2 antiferromagnetic Heisenberg chain, known as the spinon. To this end, we demonstrate how a single spinon can be excited by adding one extra spin to the ground state. This procedure accurately reproduces all key features of the spinon's dispersion. These follow from the vanishing norm of the excited state which is triggered by the ground state entanglement. Next, we show that the spinon dispersion can be approximately reproduced if we replace the true ground state with the simplest valence-bond solid. This proves that the spinon of the one-dimensional Heisenberg model can be understood as a single spin flowing through a valence-bond solid.

cond-mat.str-el↗