arXiv subjects

John T. Markert

Publications and source records attributed to John T. Markert.

5 recordsLinked to original sources

arXiv2025

Laser, Vacuum, and Gas Reaction Chamber for Operando Measurements at NSLS-II's 28-ID-2

We present a laser reaction chamber that we developed for in-situ/operando X-ray diffraction measurements at the NSLS-II 28-ID-2 XPD (X-Ray Powder Diffraction) beamline. This chamber allows for rapid and dynamic sample heating under specialized gas environments, spanning ambient conditions down to vacuum pressures. We demonstrate the capabilities of this setup through two applications: laser-driven heating in polycrystalline iron oxide and in single crystal WTe2. Our measurements reveal the ability to resolve chemical reaction kinetics over minutes with 1-s time resolution. This setup advances opportunities for in-situ/operando XRD studies in both bulk and single crystal materials.

physics.ins-det↗

arXiv2024

Alternate cleavage structure and electronic inhomogeneity in Ca-doped YBa$_2$Cu$_3$O$_{7-δ}$

YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) has favorable macroscopic superconducting properties of $T_\mathrm{c}$ up to 93 K and $H_{c2}$ up to 150 T. However, its nanoscale electronic structure remains mysterious because bulk-like electronic properties are not preserved near the surface of cleaved samples for easy access by local or surface-sensitive probes. It has been hypothesized that Ca-doping at the Y site could induce an alternate cleavage plane that mitigates this issue. We use scanning tunneling microscopy (STM) to study both Ca-free and 10% Ca-doped YBCO, and find that the Ca-doped samples do indeed cleave on an alternate plane, yielding a spatially-disordered partial (Y,Ca) layer. Our density functional theory calculations support the increased likelihood of this new cleavage plane in Ca-doped YBCO. On this surface, we image a superconducting gap with average value 24 $\pm$ 3 meV and characteristic length scale 1-2 nm, similar to Bi-based high-$T_\mathrm{c}$ cuprates, but the first map of gap inhomogeneity in the YBCO family.

cond-mat.supr-con↗

arXiv2016

Spin-Orbit Interaction and Kondo Scattering at the PrAlO$_3$/SrTiO$_3$ Interface: Effects of Oxygen Content

We report the effect of oxygen pressure during growth ($P_{O_{2}}$) on the electronic and magnetic properties of PrAlO$_3$ films grown on $\rm TiO_{2}$-terminated SrTiO$_3$ substrates. Resistivity measurements show an increase in the sheet resistance as $P_{O_{2}}$ is increased. The temperature dependence of the sheet resistance at low temperatures is consistent with Kondo theory for $P_{O_{2}} \ge 10^{-5}$ torr. Hall effect data exhibit a complex temperature dependence that suggests a compensated carrier density. We observe behavior consistent with two different types of carriers at interfaces grown at $P_{O_{2}} \ge 10^{-4}$ torr. For these interfaces, we measured a moderate positive magnetoresistance (MR) due to a strong spin-orbit (SO) interaction at low magnetic fields that evolves into a larger negative MR at high fields. Positive high MR values are associated with samples where a fraction of carriers are derived from oxygen vacancies. Analysis of the MR data permitted the extraction of the SO interaction critical field ( e.g. $ H_{SO}=$1.25 T for $P_{O_{2}}=10^{-5}$ torr). The weak anti-localization effect due to a strong SO interaction becomes smaller for higher $P_{O_{2}}$ grown samples, where MR values are dominated by the Kondo effect, particularly at high magnetic fields.

cond-mat.str-el↗

arXiv2007

Steric quenching of the switchable mirror effect Phys. Rev. B 75, 104109 (2007)

Scandium was substituted for yttrium to observe the effect of unit cell size on the optical metal-to-insulator (MIT) transition in the Y_(1-z)Sc_(z)H_(x) alloy system. The optical transmittance decreases significantly for z>0.10. Simultaneous electrical resistivity measurements confirm the transition from trihydride to dihydride behavior with increasing z. These observations imply a quenching of the MIT when the unit cell volume falls below a critical level that is consistent with the boundary between trihydride and non-trihydride forming rare-earth elements. A combinatoric model reveals this formation boundary corresponds to two or more Sc per unit cell.

cond-mat.mtrl-sci↗

arXiv2006

Quantitative Determination of the Adiabatic Condition Using Force-Detected Nuclear Magnetic Resonance

The adiabatic condition governing cyclic adiabatic inversion of proton spins in a micron-sized ammonium chloride crystal was studied using room temperature nuclear magnetic resonance force microscopy. A systematic degradation of signal-to-noise was observed as the adiabatic condition became violated. A theory of adiabatic following applicable to cyclic adiabatic inversion is reviewed and implemented to quantitatively determine an adiabaticity threshold $(γH_1)^2/(ω_{osc}Ω) = 6.0$ from our experimental results.

cond-mat.mtrl-sci↗