arXiv subjects

Hans Boschker

Publications and source records attributed to Hans Boschker.

13 recordsLinked to original sources

arXiv2025

Deposition Rates in Thermal Laser Epitaxy: Simulation and Experiment

The modeling of deposition rates in Thermal Laser Epitaxy (TLE) is essential for the accurate prediction of the evaporation process and for improved dynamic process control. We demonstrate excellent agreement between experimental data and a model based on a finite element simulation that describes the temperature distribution of an elemental source when irradiated with continuous wave laser radiation. The simulation strongly depends on the thermophysical constants of the material, data of which is lacking for many elements. Effective values for the parameters may be determined with precision by means of an unambiguous reference provided by the melting point of the material, which is directly observed during the experiments. TLE may therefore be used to study the high temperature thermophysical and optical properties of the elements.

cs.CE↗

arXiv2022

Tunable Magnetic Anisotropy in Patterned SrRuO3 Quantum Structures: Competition between Lattice Anisotropy and Oxygen Octahedral Rotation

Artificial perovskite-oxide nanostructures possess intriguing magnetic properties due to their tailorable electron-electron interactions, which are extremely sensitive to the oxygen coordination environment. To date, perovskite-oxide nanodots with sizes below 50 nm have rarely been reported. Furthermore, the oxygen octahedral distortion and its relation to magnetic properties in perovskite oxide nanodots remain unexplored yet. Here, we have studied the magnetic anisotropy in patterned SrRuO3 (SRO) nanodots as small as 30 nm while performing atomic-resolution electron microscopy and spectroscopy to directly visualize the constituent elements, in particular oxygen ions. We observe that the magnetic anisotropy and RuO6 octahedra distortion in SRO nanodots are both nanodots' size-dependent but remain unchanged in the first 3-unit-cell interfacial SRO monolayers regardless of the dots' size. Combined with the first principle calculations, we unravel a unique structural mechanism behind the nanodots' size-dependent magnetic anisotropy in SRO nanodots, sugguesting that the competition between lattice anisotropy and oxygen octahedral rotation mediates anisotropic exchange interactions in SRO nanodots. These findings demonstrate a new avenue towards tuning magnetic properties of correlated perovskite oxides and imply that patterned nanodots could be a promising playground for engineering emergent functional behaviors.

cond-mat.mtrl-sci↗

arXiv2019

Magnetic Properties of Epitaxially-grown $SrRuO_3$ Nanodots

We present the fabrication and exploration of arrays of nanodots of $SrRuO_3$ with dot sizes between 500 nm and 15 nm. Down to the smallest dot size explored, the samples were found to be magnetic with a maximum of the Curie temperature $T_C$ achieved by dots of 30 nm diameter. This peak in $T_C$ is associated with a dot-size-induced relief of the epitaxial strain, as evidenced by scanning transmission electron microscopy.

cond-mat.mes-hall↗

arXiv2018

Coherently strained epitaxial YBa$_2$Cu$_3$O$_{7-δ}$ films grown on NdGaO$_3$ (110)

YBa$_2$Cu$_3$O$_{7-δ}$ is a good candidate to systematically study high-temperature superconductivity by nanoengineering using advanced epitaxy. An essential prerequisite for these studies are coherently strained YBa$_2$Cu$_3$O$_{7-δ}$ thin films, which we present here using NdGaO$_3$ (110) as a substrate. The films are coherent up to at least 100 nm thickness and have a critical temperature of 89$\pm$1 K. The $a$ and $b$ lattice parameters of the YBa$_2$Cu$_3$O$_{7-δ}$ are matched to the in-plane lattice parameters of NdGaO$_3$ (110), resulting in a large reduction of the orthorhombicity of the YBa$_2$Cu$_3$O$_{7-δ}$. These results imply that a large amount of structural disorder in the chain layers of YBa$_2$Cu$_3$O$_{7-δ}$ is not detrimental to superconductivity.

cond-mat.supr-con↗

arXiv2018

Single-gap superconductivity and dome of superfluid density in Nb-doped SrTiO3

SrTiO$_3$ exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature \mbox{$T_\mathrm{c} \approx 0.4$~K}. Using microwave stripline resonators at frequencies from 2 to 23~GHz and temperatures down to 0.02~K, we probe the low-energy optical response of superconducting SrTiO$_3$ with charge carrier concentration from 0.3 to $2.2\times 10^{20}$~cm$^{-3}$, covering the majority of the superconducting dome. We find single-gap electrodynamics even though several electronic bands are superconducting. This is explained by a single energy gap $2Δ$ due to gap homogenization over the Fermi surface consistent with the low level of defect scattering in Nb-doped SrTiO$_3$. Furthermore, we determine $T_\mathrm{c}$, $2Δ$, and the superfluid density as a function of charge carrier concentration, and all three quantities exhibit the characteristic dome shape.

cond-mat.supr-con↗

arXiv2017

In-gap features in superconducting LaAlO$_3$-SrTiO$_3$ interfaces observed by tunneling spectroscopy

We identified quasiparticle states at well-defined energies inside the superconducting gap of the electron system at the LaAlO$_3$-SrTiO$_3$ interface using tunneling spectroscopy. The states are found only in a number of samples and depend upon the thermal-cycling history of the samples. The states consist of a peak at zero energy and other peaks at finite energies, symmetrically placed around zero energy. These peaks disappear, together with the superconducting gap, with increasing temperature and magnetic field. We discuss the likelihood of various physical mechanisms that are known to cause in-gap states in superconductors and conclude that none of these mechanisms can easily explain the results. The conceivable scenarios are the formation of Majorana bound states, Andreev bound states, or the presence of an odd-frequency spin triplet component in the superconducting order parameter.

cond-mat.supr-con↗

arXiv2016

Interface Engineering in La0.67Sr0.33MnO3-SrTiO3 Heterostructures

Interface engineering is an extremely useful tool for systematically investigating materials and the various ways materials interact with each other. We describe different interface engineering strategies designed to reveal the origin of the electric and magnetic dead-layer at La0.67Sr0.33MnO3 interfaces. La0.67Sr0.33MnO3 is a key example of a strongly correlated peroskite oxide material in which a subtle balance of competing interactions gives rise to a ferromagnetic metallic groundstate. This balance, however, is easily disrupted at interfaces. We systematically vary the dopant profile, the disorder and the oxygen octahedra rotations at the interface to investigate which mechanism is responsible for the dead layer. We find that the magnetic dead layer can be completely eliminated by compositional interface engineering such that the polar discontinuity at the interface is removed. This, however, leaves the electrical dead-layer largely intact. We find that deformations in the oxygen octahedra network at the interface are the dominant cause for the electrical dead layer.

cond-mat.mtrl-sci↗

arXiv2016

Quantum-Matter Heterostructures

Combining the power and possibilities of heterostructure engineering with the collective and emergent properties of quantum materials, quantum-matter heterostructures open a new arena of solid-state physics. Here we provide a review of interfaces and heterostructures made of quantum matter. Unique electronic states can be engineered in these structures, giving rise to unforeseeable opportunities for scientific discovery and potential applications. We discuss the present status of this nascent field of quantum-matter heterostructures, its limitations, perspectives, and challenges.

cond-mat.mtrl-sci↗

arXiv2016

Artificial Atoms Based on Correlated Materials

Low-dimensional electron systems fabricated from quantum matter have in recent years become available and are being explored with great intensity. This article gives an overview of the fundamental properties of such systems and summarizes the state of the field. We furthermore present and consider the concept of artificial atoms fabricated from quantum materials, anticipating remarkable scientific advances and possibly important applications of this new field of research. The surprising properties of these artificial atoms and of molecules or even of solids assembled from them are presented and discussed.

cond-mat.str-el↗

arXiv2015

Electron-phonon Coupling and the Superconducting Phase Diagram of the LaAlO3-SrTiO3 Interface

The superconductor at the LaAlO3-SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron-phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron-phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron-phonon coupling in relation to the superconducting phase diagram. The electron-phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band.

cond-mat.supr-con↗

arXiv2012

High temperature magnetic insulating phase in ultrathin La0.67Sr0.33MnO3 films

We present a study of the thickness dependence of magnetism and electrical conductivity in ultra thin La0.67Sr0.33MnO3 films grown on SrTiO3 (110) substrates. We found a critical thickness of 10 unit cells below which the conductivity of the films disappeared and simultaneously the Curie temperature (TC) increased, indicating a magnetic insulating phase at room temperature. These samples have a TC of about 560 K with a significant saturation magnetization of 1.2 +- 0.2 muB/Mn. The canted antiferromagnetic insulating phase in ultra thin films of n< 10 coincides with the occurrence of a higher symmetry structural phase with a different oxygen octahedra rotation pattern. Such a strain engineered phase is an interesting candidate for an insulating tunneling barrier in room temperature spin polarized tunneling devices.

cond-mat.mtrl-sci↗

arXiv2012

Preventing the reconstruction of the polar discontinuity at oxide heterointerfaces

Perovskite oxide heteroepitaxy receives much attention because of the possibility to com- bine the diverse functionalities of perovskite oxide building blocks. A general boundary con- dition for the epitaxy is the presence of polar discontinuities at heterointerfaces. These polar discontinuities result in reconstructions, often creating new functionalities at the interface. However, for a significant number of materials these reconstructions are unwanted as they alter the intrinsic materials properties at the interface. Therefore, a strategy to eliminate this reconstruction of the polar discontinuity at the interfaces is required. We show that the use of compositional interface engineering can prevent the reconstruction at the La0.67Sr0.33MnO3/SrTiO3 (LSMO/STO) interface. The polar discontinuity at this interface can be removed by the insertion of a single La0.33Sr0.67O layer, resulting in improved interface magnetization and electrical conductivity.

cond-mat.mtrl-sci↗

arXiv2010

Uniaxial contribution to the magnetic anisotropy of La0.67Sr0.33MnO3 thin films induced by orthorhombic crystal structure

La0.67Sr0.33MnO3 (LSMO) thin films under compressive strain have an orthorhombic symmetry with (1-10)o and (001)o in-plane orientations. (The subscript o denotes the orthorhombic symmetry.) Here, we grew LSMO on cubic (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates and observed a uniaxial contribution to the magnetic anisotropy which is related to the orthorhombic crystal structure. Since the lattice mismatch is equal in the two directions, the general understanding of anisotropy in LSMO, which relates the uniaxial anisotropy to differences in strain, cannot explain the results. These findings suggest that the oxygen octahedra rotations associated with the orthorhombic structure, possibly resulting in different Mn-O-Mn bond angles and therefore a change in magnetic coupling between the [1-10]o and [001]o directions, determine the anisotropy. We expect these findings to lead to a better understanding of the microscopic origin of the magnetocrystalline anisotropy in LSMO.

cond-mat.mtrl-sci↗