arXiv subjects

Kyle Shen

Publications and source records attributed to Kyle Shen.

3 recordsLinked to original sources

arXiv2026

Quasiparticle properties below coherence onset in YbAl3 nanostructures

Mesoscopic transport measurements are underexplored as probes of quasiparticles and their properties in correlated metals. The mixed valence compound YbAl$_3$ exhibits a single-ion Kondo temperature of 670 K, while thermodynamic and transport properties (probed with specific heat, magnetic susceptibility, Hall effect, and resistivity) imply the onset of coherence of heavy fermion quasiparticles at T$* \approx$ 37 K. To characterize these quasiparticles, we utilize mesoscopic techniques familiar from weakly correlated conductors. In lithographically-defined nanowires etched from epitaxial films, we observe weak antilocalization magnetoresistance and universal conductance fluctuations, consistent with electronic coherence lengths of tens of nanometers. Additionally, analysis of Johnson-Nyquist noise measurements as a function of bias current reveal, within the context of a range of accepted models, a significant electron-phonon energy loss that increases with decreasing temperature, a finding that we contextualize within the broader properties of YbAl$_3$.

cond-mat.str-el↗

arXiv2020

Computational Synthesis of Substrates by Crystal Cleavage

The discovery of novel substrate materials has been dominated by trial and error, opening the opportunity for a systematic search. To identify stable crystal surfaces, we generate bonding networks for materials from the Materials Project database with one to five atoms in the primitive unit cell. For three-dimensional crystals in this set, we systematically break up to three bonds in the bonding network of the primitive cell. Successful cleavage reduces the bonding network to two periodic dimensions, creating a layer of the cleaved crystal. We identify 4,693 unique cleavage surfaces across 2,133 bulk crystals, 4,626 of which have a maximum Miller index of 1. To characterize the likelihood of cleavage and the thermodynamic stability of the cleaved surfaces, we create monolayers of these surfaces and calculate the work of cleavage and the partially-relaxed surface energy using density functional theory to discover 3,991 potential substrates, 2,307 of which do not contain f-valence electrons and 2,183 of which are derived from a bulk precursor with an entry in the Inorganic Crystal Structure Database. Following, we identify distinct trends in the work of cleavage of these layers and relate them to metallic and covalent/ionic bonding of the three-dimensional precursor. We also assembled a database of commercially available substrates and show that the database of predicted substrates significantly enhances the diversity and range of the distribution of electronic properties and lattice parameters, providing opportunities for the epitaxial growth of many materials. We illustrate the potential impact of the substrate database by identifying several new epitaxial substrates for the transparent conductor BaSnO3, which exhibit low cleavage energies and result in strains an order of magnitude lower than currently used substrates.

cond-mat.mtrl-sci↗

arXiv2017

MBE growth of 2H-MoTe2 and 1T'-MoTe2 on 3D substrates

MoTe2 is the least explored material in the Molybdenum-chalcogen family, which crystallizes in thermodynamically stable semiconducting 2H phase at \textless 500 C and 1T' metallic phase at higher temperatures. Molecular beam epitaxy (MBE) provides an unique opportunity to tackle the small electronegativity difference between Mo and Te while growing layer by layer away from thermodynamic equilibrium. For a few-layer MoTe2 grown at a moderate rate of $\sim$6 mins per monolayer under varied Te:Mo flux ratio and substrate temperature, the boundary between the 2 phases in MBE grown MoTe2 on CaF2 is characterized using Reflection high-energy electron diffraction (RHEED), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). Grazing incidence X-ray diffraction (GI-XRD) reveals a grain size of $\sim$90 {\AA} and presence of twinned grains. XRD, transmission electron miscroscopy, RHEED, low energy electron diffraction along with lack of electrical conductivity modulation by field effect in MBE 2H-MoTe2 on GaAs (111) B show likelihood of excess Te incorporation in the films. Finally, thermal stability and air sensitivity of MBE 2H-MoTe2 is investigated by temperature dependent XRD and XPS, respectively.

cond-mat.mtrl-sci↗