arXiv subjects

Ruiheng Bai

Publications and source records attributed to Ruiheng Bai.

4 recordsLinked to original sources

arXiv2025

Flux trapping in NbTiN strips

We use scanning superconducting quantum interference device (SQUID) microscopy to image individual vortices in superconducting strips fabricated from NbTiN thin films. By repeatedly field-cooling strips of different widths in applied magnetic fields, we extract the threshold field at which the first vortex enters a strip, as well as the number and spatial configuration of vortices beyond this threshold. We model vortex behavior with and without considering the effect of pinning by numerically minimizing the Gibbs free energy of vortices in the strips. Our measurements provide a first experimental benchmark for understanding the flux trapping properties of NbTiN thin films, directly relevant to NbTiN-based superconducting circuits and devices.

cond-mat.supr-con↗

arXiv2023

Cascade of multi-electron bubble phases in monolayer graphene at high Landau level filling

The phase diagram of an interacting two-dimensional electron system in a high magnetic field is enriched by the varying form of the effective Coulomb interaction, which depends strongly on the Landau level index. While the fractional quantum Hall states that dominate in the lower energy Landau levels have been explored experimentally in a variety of two-dimensional systems, much less work has been done to explore electron solids owing to their subtle transport signatures and extreme sensitivity to disorder. Here we use chemical potential measurements to map the phase diagram of electron solid states in $N=2$, $N=3$, and $N=4$ Landau levels in monolayer graphene. Direct comparison between our data and theoretical calculations reveals a cascade of density-tuned phase transitions between electron bubble phases up to two, three or four electrons per bubble in the N=2, 3 and 4 Landau levels respectively. Finite temperature measurements are consistent with melting of the solids for T$\approx$1K.

cond-mat.mes-hall↗

arXiv2023

Scaling NbTiN-based ac-powered Josephson digital to 400M devices/cm$^2$

We describe a fabrication stackup for digital logic with 16 superconducting NbTiN layers, self-shunted a-silicon barrier Josephson Junctions (JJs), and low loss, high-$κ$ tunable HZO capacitors. The stack enables 400 MJJ/cm$^2$ device density, efficient routing, and AC power distribution on a resonant network. The materials scale beyond 28nm lithography and are compatible with standard high-temperature CMOS processes. We report initial results for two-metal layer NbTiN wires with 50nm critical dimension. A semi-ascendance wire-and-via process module using 193i lithography and 50nm critical dimension has shown cross-section uniformity of 1%=1s across the 300mm wafer, critical temperature of 12.5K, and critical current of 0.1mA at 4.2K. We also present a new design of the resonant AC power network enabled by NbTiN wires and HZO MIM capacitors. The design matches the device density and provides a 30 GHz clock with estimated efficiency of up to 90%. Finally, magnetic imaging of patterned NbTiN ground planes shows low intrinsic defectivity and consistent trapping of vorteces in 0.5 mm holes spaced on a 20 $μ$m x 20 $μ$m grid.

physics.app-ph↗

arXiv2020

Experimental determination of the energy per particle in partially filled Landau levels

We describe an experimental technique to measure the chemical potential, $μ$, in atomically thin layered materials with high sensitivity and in the static limit. We apply the technique to a high quality graphene monolayer to map out the evolution of $μ$ with carrier density throughout the N=0 and N=1 Landau levels at high magnetic field. By integrating $μ$ over filling factor, $ν$, we obtain the ground state energy per particle, which can be directly compared with numerical calculations. In the N=0 Landau level, our data show exceptional agreement with numerical calculations over the whole Landau level without adjustable parameters, as long as the screening of the Coulomb interaction by the filled Landau levels is accounted for. In the N=1 Landau level, comparison between experimental and numerical data reveals the importance of valley anisotropic interactions and the presence of valley-textured electron solids near odd filling.

cond-mat.mes-hall↗