arXiv subjects

Harry W. T. Morgan

Publications and source records attributed to Harry W. T. Morgan.

6 recordsLinked to original sources

arXiv2026

Investigation into thorium sulfate as a spinless crystal for a high-performance solid-state $^{229}Th$ nuclear clock

The $^{229}Th$ isotope has a laser-accessible nuclear transition allowing the construction of a solid-state nuclear clock. Solid-state $^{229}Th$ nuclear clock development has focused on $^{229}Th$-doped $CaF_2$ and other metal fluorides as the solid material. However, the accuracy of any fluoride-based clock will be reduced by nuclear magnetic dipole coupling to $^{19}F$ and by inhomogeneities in the thorium defect environments. Here we explore thorium sulfate, $Th(SO_4)_2$, as a solution to both problems. Strong bonding and charge delocalization in the $SO_4^{2-}$ anion may give $Th(SO_4)_2$ the wide band gap needed for a good clock. In this work we synthesize $Th(SO_4)_2$ and probe it as a nuclear clock material spectroscopically, finding that it is opaque to the 148 nm radiation that excites the $^{229}Th$ nucleus. Theoretical analysis of the optical spectra shows that charge transfer excitons are responsible for the absorption. We give guidelines for future material development and assess the prospects for $Th(SO_4)_2$ as a clock material.

cond-mat.mtrl-sci↗

arXiv2026

Defect assignment of the clock site in $^{229}\text{Th:CaF}_2$

The performance of solid-state $^{229}\text{Th}$ nuclear clocks depends sensitively on the microscopic environment of the thorium nucleus in the host crystal. Here we reassess the dominant quadrupole-split thorium site in $^{229}\text{Th:CaF}_2$, which has been assigned to a thorium dimer in recent spectroscopic work. Thermodynamic estimates, density functional theory calculations, and electric-field-gradient comparisons instead favor an isolated $\text{Th}^{4+}$ substitution on a $\text{Ca}^{2+}$ site charge-compensated by two nearby fluorine interstitials in a relaxed $90^\circ$ motif. The same calculation identifies a higher-energy mixed-shell interstitial motif as a plausible minor site. The clock-active quadrupole-split site is therefore controlled by local fluoride compensation rather than unavoidable thorium aggregation. This defect assignment also has implications for achievable linewidths and provides a microscopic basis for reducing broadening in solid-state nuclear clocks.

physics.atom-ph↗

arXiv2025

$^{229}$Th Nuclear Spectroscopy in an Opaque Material: Laser-Based Conversion Electron Mössbauer Spectroscopy of $^{229}$ThO$_2$

Here, we report the first demonstration of laser-induced conversion electron Mössbauer spectroscopy of the $^{229}$Th nuclear isomeric state, which provides the ability to probe the nuclear transition in a material that is opaque to light resonant with the nuclear transition. Specifically, we excite the nuclear transition in a thin ThO$_2$ sample whose band gap ($\sim$ 6 eV) is considerably smaller than the nuclear isomeric state energy (8.4 eV). As a result, the excited nucleus can quickly decay by internal conversion, resulting in the ejection of electrons from the surface. By collecting these conversion electrons, nuclear spectroscopy can be recorded. Unlike fluorescence spectroscopy, this technique is compatible with materials whose work function is less than the nuclear transition energy, opening a wider class of systems to study. Further, because ThO$_2$ can be made from spinless isotopes and the internal conversion decay process reduces the isomeric state lifetime to only $\sim$10 $μ$s, allowing $\sim$10$^8$ relative reduction in clock interrogation time, a conversion-electron-based nuclear clock could lead to a $\sim$10$^4$ reduction in clock instability.

physics.atom-ph↗

arXiv2025

Mapping the three-dimensional fermiology of the triangular lattice magnet EuAg$_4$Sb$_2$

In this paper, we report the temperature-field phase diagram as well as present a comprehensive study of the electronic structure and three-dimensional fermiology of the triangular-lattice magnet EuAg$_4$Sb$_2$, utilizing quantum oscillation measurements, angle-resolved photoemission spectroscopy and first-principles calculations. The complex magnetic phase diagram of EuAg$_4$Sb$_2$ highlights many transitions through nontrivial AFM states. Shubnikov-de Haas and de Haas-van Alphen oscillations were observed in the polarized ferromagnetic state of EuAg$_4$Sb$_2$, revealing three pairs of distinct spin-split frequency branches with small effective masses. A comparison of the angle-dependent oscillation data with first-principles calculations in the ferromagnetic state and angle-resolved photoemission spectra shows good agreement, identifying tubular hole pockets and hourglass-shaped hole pockets at the Brillouin zone center, as well as diamond-shaped electron pockets at the zone boundary. As the temperature increases, the frequency branches of the tiny hourglass pockets evolve into a more cylindrical shape, while the larger pockets remain unchanged. This highlights that variations in exchange splitting, driven by changes in the magnetic moment, primarily impact the small Fermi pockets without significantly altering the overall band structure. This is consistent with first-principles calculations, which show minimal changes near the Fermi level across ferromagnetic and simple antiferromagnetic states or under varying on-site Coulomb repulsion.

cond-mat.mtrl-sci↗

arXiv2024

Bottom-up approach to scalable growth of molecules capable of optical cycling

Gas-phase molecules capable of repeatable, narrow-band spontaneous photon scattering are prized for direct laser cooling and quantum state detection. Recently, large molecules incorporating phenyl rings have been shown to exhibit similar vibrational closure to the small molecules demonstrated so far, and it is not yet known if the high vibrational-mode density of even larger species will eventually compromise optical cycling. Here, we systematically increase the size of hydrocarbon ligands attached to single alkaline-earth-phenoxides from (-H) to -C$_{14}$H$_{19}$ while measuring the vibrational branching fractions of the optical transition. We find that varying the ligand size from 1 to more than 30 atoms does not systematically reduce the cycle closure, which remains around 90%. Theoretical extensions to larger diamondoids and bulk diamond surface suggest that alkaline earth phenoxides may maintain the desirable scattering behavior as the system size grows further, with no indication of an upper limit.

physics.chem-ph↗

arXiv2024

Fermiology and transport properties of the proposed topological crystalline insulator SrAg4Sb2

Compared to time-reversal symmetry-protected Z2 topological insulators and Dirac/Weyl semimetals, there are significantly fewer candidates for topological crystalline insulators. SrAg4Sb2 is predicted to exhibit topological crystalline insulator behavior when considering spin-orbit coupling. In this study, we systematically investigate single crystals of SrAg4Sb2 using electrical transport and magnetic torque measurements, along with first-principles calculations. Our transport data reveals its compensated semimetal nature with a magnetoresistance up to around 700% at 2 K and 9 T. Analysis of de Haas-van Alphen oscillations uncovers a Fermi surface consisting of three distinct Fermi pockets with light effective masses. Comparison between the three-dimensional fermiology obtained from our oscillation data and the first-principles calculations demonstrates excellent agreement. This confirms the accuracy of the calculations, which indicate a band inversion centered at the Γ point and identify the existence of nontrivial tube and needle hole Fermi pockets at Γ, alongside one trivial diamond electron pocket at the T point in the Brillouin zone. Furthermore, symmetry and topology analysis results in two potential sets of topological invariants, suggesting the emergence of two-dimensional gapless Dirac surface states either on the ab planes or on both the ab planes and mirror planes, protected by crystal symmetries. Therefore, SrAg4Sb2 emerges as a promising candidate topological crystalline insulator.

cond-mat.mtrl-sci↗