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1. Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

   https://doi.org/10.1088/1367-2630/ace471  

   Jadbabaie, Arian ; Takahashi, Yuiki ; Pilgram, Nickolas H ; Conn, Chandler J ; Zeng, Yi ; Zhang, Chi ; Hutzler, Nicholas R ( July 2023 , New Journal of Physics)

   Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of${}^{174}$YbOH using high-resolution optical spectroscopy on the nominally forbidden$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$$\to \tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the$\tilde{X}{}^2{\mathrm{\Sigma }}^{+}(010)$state and fit the molecule-frame dipole moment to$D_{\mathrm{m}\mathrm{o}\mathrm{l}}=2.16(1)$Dand the effective electrong-factor to$g_S=2.07(2)$. Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excited$\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}(000)$state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

    

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2. Superconducting Phases in Lithium Decorated Graphene LiC6

   https://doi.org/10.1038/s41598-018-32050-9  

   Gholami, Rouhollah ; Moradian, Rostam ; Moradian, Sina ; Pickett, Warren E. ( September 2018 , Scientific Reports)

   A study of possible superconducting phases of graphene has been constructed in detail. A realistic tight binding model, fit to ab initio calculations, accounts for the Li-decoration of graphene with broken lattice symmetry, and includessanddsymmetry Bloch character that influences the gap symmetries that can arise. The resulting seven hybridized Li-C orbitals that support nine possible bond pairing amplitudes. The gap equation is solved for all possible gap symmetries. One band is weakly dispersive near the Fermi energy along Γ → Mwhere its Bloch wave function has linear combination of$${d}_{{x}^{2}-{y}^{2}}$$$d_{x^2-y^2}$andd_xycharacter, and is responsible for$${d}_{{x}^{2}-{y}^{2}}$$$d_{x^2-y^2}$andd_xypairing with lowest pairing energy in our model. These symmetries almost preserve properties from a two band model of pristine graphene. Another part of this band, alongK → Γ, is nearly degenerate with uppersband that favors extendedswave pairing which is not found in two band model. Upon electron doping to a critical chemical potentialμ₁ = 0.22 eVthe pairing potential decreases, then increases until a second critical valueμ₂ = 1.3 eV at which a phase transition to a distorteds-wave occurs. The distortion ofd- or s-wave phases are a consequence of decoration which is not appear in two band pristine model. In the pristine graphene these phases convert to usuald-wave or extendeds-wave pairing.

    

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3. Spectroscopy of the 85 Rb 4 D3/2 state for hyperfine-structure determination

   https://doi.org/10.1088/1367-2630/acf405  

   Duspayev, A. ; Raithel, G. ( September 2023 , New Journal of Physics)

   We report a measurement of the hyperfine-structure constants of the⁸⁵Rb 4$D_{3/2}$state using two-photon optical spectroscopy of the 5$S_{1/2}\to$4$D_{3/2}$transition. The spectra are acquired by measuring the transmission of the low-power 795 nm lower-stage laser beam through a cold-atom sample as a function of laser frequency, with the frequency of the upper-stage, 1476 nm laser fixed. All 4 hyperfine components of the$4D_{3/2}$state are well-resolved in the experimental data. The dominant systematic is the light shift from the 1476 nm laser, which is addressed by extrapolating line positions measured for a set of 1476 nm laser powers to zero laser power. The analysis of our experimental data yields both the magnetic-dipole and electric-quadrupole constants for the⁸⁵Rb 4$D_{3/2}$level, without using earlier hyperfine measurements of other atomic levels. The respective results,$A=$7.419(35) MHz and$B=$4.19(19) MHz, are discussed in context with previous works. Our investigation may be useful for optical atomic clocks for precision metrology and emerging atom-based quantum technologies, all-infrared excitation of Rb Rydberg levels, and molecular physics.

    

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4. The influence of crystal thickness and interlayer interactions on the properties of heavy ion irradiated MoS 2

   https://doi.org/10.1088/2053-1583/ab817b  

   Isherwood, Liam H. ; Hennighausen, Zachariah ; Son, Seok-Kyun ; Spencer, Ben F. ; Wady, Paul T. ; Shubeita, Samir M. ; Kar, Swastik ; Casiraghi, Cinzia ; Baidak, Aliaksandr ( May 2020 , 2D Materials)

   Ion irradiation is a versatile tool to introduce controlled defects into two-dimensional (2D) MoS₂on account of its unique spatial resolution and plethora of ion types and energies available. In order to fully realise the potential of this technique, a holistic understanding of ion-induced defect production in 2D MoS₂crystals of different thicknesses is mandatory. X-ray photoelectron spectroscopy, electron diffraction and Raman spectroscopy show that thinner MoS₂crystals are more susceptible to radiation damage caused by 225 keV Xe⁺ions. However, the rate of defect production in quadrilayer and bulk crystals is not significantly different under our experimental conditions. The rate at which S atoms are sputtered as a function of radiation exposure is considerably higher for monolayer MoS₂, compared to bulk crystals, leading to MoO₃formation. P-doping of MoS₂is observed and attributed to the acceptor states introduced by vacancies and charge transfer interactions with adsorbed species. Moreover, the out-of-plane vibrational properties of irradiated MoS₂crystals are shown to be strongly thickness-dependent: in mono- and bilayer MoS₂, the confinement of phonons by defects results in a blueshift of the$A_{1g}$mode. Whereas, a redshift is observed in bulk crystals due to attenuation of the effective restoring forces acting on S atoms caused by vacancies in adjacent MoS₂layers. Consequently, the$A_{1g}$frequency of tri- and quadrilayer crystals is statistically invariant on account oft competition between phonon confinement effects and interlayer interactions. The$A_{1g}$linewidth is observed to decrease in bi- and trilayer crystals after low dose irradiation and is attributed to layer decoupling. This work shows that there is a complex interplay between defect production, crystal thickness and interlayer interactions in MoS₂. Our results demonstrate that ion irradiation is an effective tool to modulate the electronic, vibrational and structural properties of MoS₂, which may prove beneficial for practical applications.

    

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5. Charge state-dependent symmetry breaking of atomic defects in transition metal dichalcogenides

   https://doi.org/10.1038/s41467-024-47039-4  

   Xiang, Feifei ; Huberich, Lysander ; Vargas, Preston A. ; Torsi, Riccardo ; Allerbeck, Jonas ; Tan, Anne Marie Z. ; Dong, Chengye ; Ruffieux, Pascal ; Fasel, Roman ; Gröning, Oliver ; et al ( March 2024 , Nature Communications)

   The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. Here we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS₂by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By changing the built-in substrate chemical potential, different charge states of sulfur vacancies (Vac_S) and substitutional rhenium dopants (Re_Mo) can be stabilized. Vac$${}_{{{{{{{{\rm{S}}}}}}}}}^{-1}$$${}_S^{-1}$as well as Re$${}_{{{{{{{{\rm{Mo}}}}}}}}}^{0}$$${}_{\mathrm{Mo}}^0$and Re$${}_{{{{{{{{\rm{Mo}}}}}}}}}^{-1}$$${}_{\mathrm{Mo}}^{-1}$exhibit local lattice distortions and symmetry-broken defect orbitals attributed to a Jahn-Teller effect (JTE) and pseudo-JTE, respectively. By mapping the electronic and geometric structure of single point defects, we disentangle the effects of spatial averaging, charge multistability, configurational dynamics, and external perturbations that often mask the presence of local symmetry breaking.

    

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