arXiv subjects

Adam V. Bruce

Publications and source records attributed to Adam V. Bruce.

4 recordsLinked to original sources

arXiv2026

High-Temporal-Resolution Measurements of the Impacts of Ionizing Radiation on Superconducting Qubits

We measure the effect of ionizing radiation on superconducting qubits with a timing resolution of 1 $\mu s$ using microwave kinetic inductance detectors (MKIDs) fabricated on the same substrate. We observe no correlation between two-level system (TLS) scrambling events and ionizing radiation events detected with the MKIDs, suggesting TLS scrambling events may not arise from ionizing radiation and instead the previously reported apparent correlation may be due to events without sufficient energy to trigger our MKIDs. We characterize the fast-time system recovery of transmons following a radiation event, where we observe the recovery of the enhanced qubit relaxation and excitation to be well-described by an exponential recovery to the baseline quasiparticle density, with a characteristic time of $13\pm1\ \mu$s, and a peak quasiparticle density at the junction per deposited energy of $240/\mu m^3/MeV$. The fast recovery is consistent with literature reported values for Nb-based devices with direct injection of 2$\Delta_{\text{Al}}$ phonons, demonstrating the recovery is strongly dependent on the proximity of niobium to the junction.

quant-ph↗

arXiv2025

Tuning the Magnetic Anisotropy Energy of MoS$_2$-supported Mn$_{12}$ complexes by Electric Field: A First-Principles Study

In this work, we examine low-energy adsorption configurations of four dodecanuclear manganese single-molecule magnets [Mn$_{12}$O$_{12}$(O$_2$CR)$_{16}$(H$_2$O)$_4$] (Mn$_{12}$), where the ligand R being H, CH$_3$, CHCl$_2$ or C$_6$H$_5$, on a molybdenum disulfide (MoS$_2$) monolayer using force field and density functional theory calculations. The van der Waals interaction is shown to be crucial for determining the adsorption energy. Some electrons transfer from the substrate to the molecules upon surface adsorption, resulting in a reduction of the magnetic anisotropy energy of Mn$_{12}$. Since the lowest unoccupied molecular orbital of Mn$_{12}$ is close to the valence band of MoS$_2$, a negative electric field is more effective in modulating charge transfer and energy band alignment, and thus altering the magnetic anisotropy energy, compared with a positive electric field. A significant increase in the magnetic anisotropy energy of Mn$_{12}$ with the ligand R=CHCl$_2$ or R=C$_6$H$_5$ under a sufficiently high electric field has been predicted. Our calculations show that the molecules remain intact on the surface both before and after the electric field is applied. Finally, a two-level system formed by different adsorption configurations is evaluated, and the tunability of its energy barrier under an electric field is demonstrated. Our study sheds light on tuning the properties of single-molecule magnets using an electric field, when the molecules are supported on a surface.

cond-mat.mtrl-sci↗

arXiv2022

Clar's goblet on graphene: field modulated charge transfer in a hydrocarbon heterostructure

In certain configurations, the aromatic properties of benzene ring structured molecules allow for unpaired, reactive valence electrons (known as radicals). Clar's goblets are such molecules. With an even number of unpaired radicals, these nanographenes are topologically frustrated hydrocarbons in which pi-bonding network and topology of edges give rise to the magnetism. Clar's goblets are therefore valued as prospective qubits provided they can be modulated between magnetic states. Using first principles DFT, we demonstrate the effects of adsorption on both molecule and substrate in a graphene-Clar's goblet heterostructure. We look at the energy difference bewteen FM and AFM states of the system and discuss underlying physical and chemical mechanisms in reference to the highest occupied molecular orbital (HOMO) and second HOMO (HOMO-1). We find that the HOMO of the molecule in the FM state is right at the Fermi surface, which leads to the hybridization between molecular state and the graphene state near the Dirac point. Furthermore, we investigate qualitative changes in charge realignment and magnetic state under variable electric field. Transitions from FM to AFM and back to FM states are observed.

cond-mat.mes-hall↗

arXiv2022

Insights to negative differential resistance in \texorpdfstring{MoS\textsubscript{2}}{MoS2} Esaki diodes: a first-principles perspective

\ce{MoS_2} is a two dimensional material with a band gap depending on the number of layers and tunable by an external electric field. The experimentally observed intralayer band-to-band tunneling and interlayer band-to-band tunneling in this material present an opportunity for new electronic applications in tunnel field effect transistors. However, such a widely accepted concept has never been supported up by theoretical investigations based on first principles. In this work, using density functional theory, in conjunction with non-equilibrilibrium Green's function techniques and our electric field gating method, enabled by a large-scale computational approach, we study the relation between band alignment and transmission in planar and side-stack \ce{MoS_2} $p$-$i$-$n$ junction configurations. We demonstrate the presence of negative differential resistance for both in-plane and interlayer current, a staple characteristic of tunnel diode junctions, and analyze the physical origin of such an effect. Electrostatic potentials, the van der Waals barrier, and complex band analysis are also examined for a thorough understanding of Esaki Diodes.

cond-mat.mes-hall↗