arXiv subjects

Nicholas S. Bingham

Publications and source records attributed to Nicholas S. Bingham.

10 recordsLinked to original sources

arXiv2026

Growth of (111)-textured SrTiO3 thin films on Pt(111)/Al2O3(1-102) substrates by rf magnetron sputter deposition

SrTiO3 thin films, 20-30nm, with high quality crystal structure and low roughness can be used as growth templates for complex oxides or as the dielectric materials for capacitor structures. In this work, stoichiometric STO thin films were grown by radio frequency magnetron sputtering on Pt (111) templates grown on rAl2O3 substrates, and the effects of growth parameters as well as the underlying Pt templates structural properties on the quality of STO films were studied. A comparison between room temp grown Pt and Pt grown at elevated temps showed that the latter lead to highly ordered Pt and STO films with quasi 2D surface roughness. Xray diffraction showed that the STO thin films had (111) and (222) crystal orientation. A rocking curve full width at half maximum value of 0.2° was achieved, indicating that the STO films are high-quality. The STO films have a roughness less than 1 nm, as measured using atomic force microscopy, comparable to the underlying Pt templates roughness.

cond-mat.mtrl-sci↗

arXiv2026

Thermal Corrections and Analysis on the Phase Stability of CsPbCl3 and Cs2AgSbCl6 during In-Situ Thermal Treatment

Cesium lead chloride (CsPbCl3) is a well known and principal model for inorganic perovskite halide optoelectronic research. The many available techniques including high temperature stability testing have been used to investigate the increasing interest in inorganic perovskites as primary layers in solar cell applications. Due to the nature of high temperature testing, the characterization technique, reproducibility, and the true sample temperature are vital in determining relative stability. By choosing CsPbCl3 in the investigation of the structural stability of perovskites at high temperatures, it acts as a baseline to create and verify a methodology that accurately probes sample temperature, phase transitions, and decomposition onsets. Therefore, we present a methodological approach to investigate the thermal interactions and stability of CsPbCl3 as a parent single perovskite halide based on ligand-assisted re-precipitation synthesis techniques. Where we use our approach to inform and probe thermal interactions in other cesium/chlorine compounds like Cs2AgSbCl6. By analyzing the stoichiometry and initial phases through investigations of the crystalline structure and particle morphology, we calculated temperature conversions using a control substrate and refinements to best estimate changing structure parameters. Using in-situ temperature dependent X-ray diffraction, we were able to effectively probe the phase transitions and decomposition temperatures of the investigated halide powders. Creating a process that can confirm known high temperature structural phenomena of model perovskite halides while verifying our true sample temperature. Which allowed for further testing on the thermal kinetics of on the double perovskite structure Cs2AgSbCl6 and will continue to allow us to test other perovskites and perovskite families of interest in modern high temperature perovskite halide research.

cond-mat.mtrl-sci↗

arXiv2025

THz carrier dynamics in $SrTiO_{3}/LaTiO_{3}$ interface two-dimensional electron gases

A two-dimensional electron gas (2DEG) forms at the interface of complex oxides like $SrTiO_{3}$ (STO) and $LaTiO_{3}$ (LTO), despite each material having a low native conductivity, as a band and a Mott insulator, respectively. The interface 2DEG hosts charge carriers with moderate charge carrier density and mobility that raised interest as a material system for applications like field-effect transistors or detectors. Of particular interest is the integration of these oxide systems in silicon technology. To this end we study the carrier dynamics in a STO/LTO/STO heterostructure epitaxially grown on Si(001) both experimentally and theoretically. Linear THz spectroscopy was performed to analyze the temperature dependent charge carrier density and mobility, which was found to be in the range of $10^{12}$ $cm^2$ and 1000 $cm^2V^{-1}s^{-1}$, respectively. Pump-probe measurements revealed a very minor optical nonlinearity caused by hot carriers with a relaxation time of several 10 ps, even at low temperature. Density functional theory calculations with a Hubbard U term on ultrathin STO-capped LTO films on STO(001) show an effective mass of 0.64-0.68 $m_{e}$.

cond-mat.mtrl-sci↗

arXiv2023

Topological Kinetic Crossover in a Nanomagnet Array

Ergodic kinetics, which are critical to equilibrium thermodynamics, can be constrained by a system's topology. We study a model nanomagnetic array in which such constraints visibly affect the behavior. In this system, magnetic excitations connect into thermally active one-dimensional strings whose motion can be imaged in real time. At high temperatures, we observe the merging, breaking, and reconnecting of strings, resulting in the system transitioning between topologically distinct configurations. Below a crossover temperature, the string motion is dominated by simple changes in length and shape. In this low temperature regime, the system is energetically stable because of its inability to explore all possible topological configurations. This kinetic crossover suggests a generalizable conception of topologically broken ergodicity and limited equilibration.

cond-mat.mes-hall↗

arXiv2022

Entropy-driven order in an array of nanomagnets

Long-range ordering is typically associated with a decrease in entropy. Yet, it can also be driven by increasing entropy in certain special cases. We demonstrate that artificial spin ice arrays of single-domain nanomagnets can be designed to produce entropy-driven order. We focus on the tetris artificial spin ice structure, a highly frustrated array geometry with a zero-point Pauli entropy, which is formed by selectively creating regular vacancies on the canonical square ice lattice. We probe thermally active tetris artificial spin ice both experimentally and through simulations, measuring the magnetic moments of the individual nanomagnets. We find two-dimensional magnetic ordering in one subset of these moments, which we demonstrate to be induced by disorder (i.e., increased entropy) in another subset of the moments. In contrast with other entropy-driven systems, the discrete degrees of freedom in tetris artificial spin ice are binary and are both designable and directly observable at the microscale, and the entropy of the system is precisely calculable in simulations. This example, in which the system's interactions and ground state entropy are well-defined, expands the experimental landscape for the study of entropy-driven ordering.

cond-mat.mes-hall↗

arXiv2021

String Phase in an Artificial Spin Ice

One-dimensional strings of local excitations are a fascinating feature of the physical behavior of strongly correlated topological quantum matter. Here we study strings of local excitations in a classical system of interacting nanomagnets, the Santa Fe Ice geometry of artificial spin ice. We measured the moment configuration of the nanomagnets, both after annealing near the ferromagnetic Curie point and in a thermally dynamic state. While the Santa Fe Ice lattice structure is complex, we demonstrate that its disordered magnetic state is naturally described within a framework of emergent strings. We show experimentally that the string length follows a simple Boltzmann distribution with an energy scale that is associated with the system's magnetic interactions and is consistent with theoretical predictions. The results demonstrate that string description and associated topological characteristics are not unique to quantum models but can also provide a simplifying description of complex classical systems with non-trivial frustration.

cond-mat.mes-hall↗

arXiv2020

Experimental Observation of Vortex Rings in a Bulk Magnet

Vortex rings are remarkably stable structures occurring in numerous systems: for example in turbulent gases, where they are at the origin of weather phenomena [1]; in fluids with implications for biology [2]; in electromagnetic discharges [3]; and in plasmas [4]. While vortex rings have also been predicted to exist in ferromagnets [5], they have not yet been observed. Using X-ray magnetic nanotomography [6], we imaged three-dimensional structures forming closed loops in a bulk micromagnet, each composed of a vortex-antivortex pair. Based on the magnetic vorticity, a quantity analogous to hydrodynamic vorticity, we identify these configurations as magnetic vortex rings. While such structures have been predicted to exist as transient states in exchange ferromagnets [5], the vortex rings we observe exist as stable, static configurations, whose stability we attribute to the dipolar interaction. In addition, we observe stable vortex loops intersected by magnetic singularities [7], at which the magnetisation within the vortex and antivortex cores reverses. We gain insight into the stability of these states through field and thermal equilibration protocols. These measurements pave the way for the observation of complex three-dimensional solitons in bulk magnets, as well as for the development of applications based on three-dimensional magnetic structures.

cond-mat.mes-hall↗

arXiv2019

Understanding Thermal Annealing of Artificial Spin Ice

We have performed a detailed study of thermal annealing of the moment configuration in artificial spin ice. Permalloy (Ni$_{80}$Fe$_{20}$) artificial spin ice samples were examined in the prototypical square ice geometry, studying annealing as a function of island thickness, island shape, and annealing temperature and duration. We also measured the Curie temperature as a function of film thickness, finding that thickness has a strong effect on the Curie temperature in regimes of relevance to many studies of the dynamics of artificial spin ice systems. Increasing the interaction energy between island moments and reducing the energy barrier to flipping the island moments allows the system to more closely approach the collective low energy state of the moments upon annealing, suggesting new channels for understanding the thermalization processes in these important model systems.

cond-mat.mes-hall↗

arXiv2017

Single-axis dependent structural and multiferroic properties of orthorhombic RMnO$_3$ (R = Gd - Lu)

Controlling material properties by modulating the crystalline structure has been attempted using various techniques, e.g., hydrostatic pressure, chemical pressure, and epitaxy. These techniques succeed to improve properties and achieve desired functionalities by changing the unit cell in all dimensions. In order to obtain a more detailed understanding on the relation between the crystal lattice and material properties, it is desirable to investigate the influence of a smaller number of parameters. Here, we utilize the combination of chemical pressure and epitaxy to modify a single lattice parameter of the multiferroic orthorhombic RMnO$_3$ (R = rare-earth, o-RMnO$_3$) system. By growing a series of o-RMnO$_3$ (R = Gd - Lu) films coherently on (010)-oriented YAlO$_3$ substrates, the influence of chemical pressure is reflected only along the $b$-axis. Thus, a series of o-RMnO$_3$ with $a$ ~ 5.18 Å, 5.77 Å < $b$ < 5.98 Å, and $c$ ~ 7.37 Å were obtained. Raman spectra analysis reveals that the change of the $b$-axis parameter induces a shift of the oxygen in the nominally "fixed" $ca$-plane. Their ferroelectric ground state is independent on the $b$-axis parameter showing polarization of ~ 1 $μ$C cm$^{-2}$ along the $a$-axis for the above-mentioned range, except for $b$ ~ 5.94 Å which corresponds to TbMnO$_3$ showing ~ 2 $μ$C cm$^{-2}$. This result implies that multiferroic order of o-RMnO$_3$ is almost robust against the $b$-axis parameter provided that the dimension of the $ca$-plane is fixed to 7.37 Å $\times$ 5.18 Å.

cond-mat.mtrl-sci↗

arXiv2008

Light Assisted Collisional Loss in a $^{85/87}$Rb Ultracold Optical Trap

We have studied hetero- and homonuclear excited state/ground state collisions by loading both $^{85}$Rb and $^{87}$Rb into a far off resonant trap (FORT). Because of the relatively weak confinement of the FORT, we expect the hyperfine structure of the different isotopes to play a crucial role in the collision rates. This dependence on hyperfine structure allows us to measure collisions associated with long range interatomic potentials of different structure: such as long and short ranged; or such as purely attractive, purely repulsive, or mixed attractive and repulsive. We observe significantly different loss rates for different excited state potentials. Additionally, we observe that some collisional channels' loss rates are saturated at our operating intensities (~15 mW/cm$^{2}$). These losses are important limitations in loading dual isotope optical traps.

physics.atom-ph↗