Diamagnetic Atoms Research Articles

Electric dipole moments in 5+3 flavor weak effective theory

A fully generic treatment of electric dipole moments (EDMs) is presented in the CP-violating and flavor-conserving weak effective field theory (WET) with five flavors of quarks and three flavors of leptons. We systematically analyze leading contributions to EDMs originating from QCD and QED renormalization group running between the electroweak scale and low energy scales of about 2 GeV. We include the full one-loop anomalous dimension and a subset of two-loop corrections, as well as threshold corrections at the bottom, charm and τ masses. This allows us to derive master formulae in the space of generic WET for the neutron and proton EDMs, for EDMs of diamagnetic atoms, and for the precession frequencies constrained in molecular EDM experiments, from which bounds on the electron EDM are extracted. In particular, our master formulae capture the contributions of WET CP-violating operators with heavy quark and lepton flavors. As an application, we study EDM constraints on the Yukawa couplings of the Higgs boson, in both the linear and non-linear realizations of electroweak symmetry breaking.

Effect of Cobalt on the Microstructure of Fe-B-Sn Amorphous Metallic Alloys

Fe78B15Sn7 and (Fe3Co1)78B15Sn7 amorphous metallic alloys were prepared using the method of planar flow casting. The amorphous nature of ribbons containing 7 at. % Sn was verified by X-ray diffraction. The resulting chemical composition was checked by flame atomic absorption spectroscopy and by mass spectrometry with inductively coupled plasma. The microstructure of the as-quenched metallic glasses was investigated by 57-Fe and 119-Sn Mössbauer spectrometry. The experiments were performed with transmission geometry at 300 K, 100 K, and 4.2 K, and in an external magnetic field of 6 T. The replacement of a quarter of the Fe by Co did not cause significant modifications of the hyperfine interactions in the 57-Fe nuclei. The observed minor variations in the local magnetic microstructure were attributed to alterations in the topological short-range order. However, the in-field 57-Fe Mössbauer spectra indicated a misalignment of the partial magnetic moments. On the other hand, the presence of Co considerably affected the local magnetic microstructure of the 119-Sn nuclei. This was probably due to the higher magnetic moment of Co, which induces transfer fields and polarization effects on the diamagnetic Sn atoms.

COMPLEX OF LABORATORY GROWTH FACILITIES FOR SOLUTION–MELT SYNTHESIS CRYSTALS OF IRON BORATE FeBO3 AND CRYSTALS OF SOLID SOLUTIONS ON ITS BASIS

A complex of laboratory growth facilities, designed for solution–melt synthesis of highly perfect single crystals of iron borate, as well as crystals based on this compound, has been developed and constructed. Equipping growth plants with program-controlled functional units makes it possible to fully automate the technological process. As a result of test experiments single crystals of iron borate FeBO3 and single crystals doped with diamagnetic gallium atoms, Fe1-xGaxBO3, were obtained. The high structural perfection of the synthesized samples was confirmed by X-ray diffraction analysis and high-resolution electron microscopy.

Prospects for assembling ultracold radioactive molecules from laser-cooled atoms

Molecules with unstable isotopes often contain heavy and deformed nuclei and thus possess a high sensitivity to parity-violating effects, such as the Schiff moments. Currently the best limits on Schiff moments are set with diamagnetic atoms. Polar molecules with quantum-enhanced sensing capabilities, however, can offer better sensitivity. In this work, we consider the prototypical 223Fr107Ag molecule, as the octupole deformation of the unstable 223Fr francium nucleus amplifies the nuclear Schiff moment of the molecule by two orders of magnitude relative to that of spherical nuclei and as the silver atom has a large electron affinity. To develop a competitive experimental platform based on molecular quantum systems, 223Fr atoms and 107Ag atoms have to be brought together at ultracold temperatures. That is, we explore the prospects of forming 223Fr107Ag from laser-cooled Fr and Ag atoms. We have performed fully relativistic electronic-structure calculations of ground and excited states of FrAg that account for the strong spin-dependent relativistic effects of Fr and the strong ionic bond to Ag. In addition, we predict the nearest-neighbor densities of magnetic-field Feshbach resonances in ultracold 223Fr + 107Ag collisions with coupled-channel calculations. These resonances can be used for magneto-association into ultracold, weakly-bound FrAg. We also determine the conditions for creating 223Fr107Ag molecules in their absolute ground state from these weakly-bound dimers via stimulated Raman adiabatic passage using our calculations of the relativistic transition electric dipole moments.

Переход Пайерлса в линейной цепочке обменно связанных спинов

The loss of stability of the antiferromagnetic state of matter respective to the Peierls transition is calculated in the framework of a new model of magnetic sublattices. In this new model, in contrast to the Anderson-Ziman sublattice model, the antiferromagnetic spin ordering is provided by a weak influence of magnetic anisotropy. Magnetic anisotropy suppresses exchange mixing with a sufficiently large number of spins in the sublattice . The Peierls transition consists in the deformation in a linear chain of atoms, namely the convergence of neighboring atoms, at which the period of the crystal lattice increases by factor of two. When atoms approach, exchange interaction is established between a pair of nearest atomic spins only. Based on the new model of magnetic sublattices, the antiferromagnetic sublattice state of the periodic chain of spins is found to be unstable respective to the transition to the Peierls state. During the transition to the "spin-Peierls" state, the spins of neighboring atoms will be ordered antiparallelly, but since there is no preferred direction of spin ordering, it is impossible to introduce the concept of magnetic sublattices. Such magnetic states can be suggested from the exponential dependence of the magnetic susceptibility on the reciprocal temperature. The electrons magnetism in this state is determined by the atomic diamagnetism if the frequencies of thermal motion are small compared to the exchange frequency.

(Invited) The Role of Gd in the Dy2GdN@C80 single Molecule Magnet

Endohedral fullerenes are perfect nanolaboratories for the study of 4f electron magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with magnetically isotropic gadolinium decreases the stability of a given magnetization that is imposed by the Dy2 unit and demonstrates Gd to accelerate the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that Gd also affects the magnetic ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in Dy2GdN@C80. This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation [1].[1] Gadolinium as a single atom catalyst in a single molecule magnet, Aram Kostanyan, Christin Schlesier, Rasmus Westerstrom, Jan Dreiser, Fabian Fritz, Bernd Buchner, Alexey A. Popov, Cinthia Piamonteze, Thomas Greber, arXiv:2009.12259 September (2020).The figure shows the Dy2GdN@C80 molecule where the two Dy 4f9 and the Gd 4f7 orbitals of the paramagnetic entities are shown in red. Note the orientation of the Jz=15/2 Dy 4f9 orbitals towards the N3- ligand. Picture by Ari P. Seitsonen. Figure 1

Screening of nucleon electric dipole moments in atomic systems

The electric dipole moments (EDMs) of diamagnetic atoms are expected to be sensitive to charge-parity violation particularly in nuclei through the nuclear Schiff moment. I explicitly demonstrate that the well-known form of the Schiff moment operator originating from the nucleon EDM is obtained by considering the screening of the nucleon EDMs in a neutral atom. Consequently, an additional contribution to the Schiff moment arises from the screening of the nuclear EDM induced by the interaction of the nucleon EDMs with the protons. This correction to the Schiff moment of $^{199}$Hg is evaluated in the independent particle model.

Renormalization of CP -violating nuclear forces

Electric dipole moments of nuclei, diamagnetic atoms, and certain molecules are induced by CP-violating nuclear forces. Naive dimensional analysis predicts these forces to be dominated by long-range one-pion-exchange processes, with short-range forces entering only at next-to-next-to-leading order in the chiral expansion. Based on renormalization arguments we argue that a consistent picture of CP-violating nuclear forces requires a leading-order short-distance operator contributing to ${}^1S_0$-${}^3P_0$ transitions, due to the attractive and singular nature of the strong tensor force in the ${}^3P_0$ channel. The short-distance operator leads to $\mathcal O(1)$ corrections to static and oscillating, relevant for axion searches, electric dipole moments. We discuss strategies how the finite part of the associated low-energy constant can be determined in the case of CP violation from the QCD theta term by the connection to charge-symmetry violation in nuclear systems.

Probing Fundamental Symmetries of Deformed Nuclei in Symmetric Top Molecules

Precision measurements of Schiff moments in heavy, deformed nuclei are sensitive probes of beyond standard model T, P violation in the hadronic sector. While the most stringent limits on Schiff moments to date are set with diamagnetic atoms, polar polyatomic molecules can offer higher sensitivities with unique experimental advantages. In particular, symmetric top molecular ions possess K doublets of opposite parity with especially small splittings, leading to full polarization at low fields, internal comagnetometer states useful for rejection of systematic effects, and the ability to perform sensitive searches for T, P violation using a small number of trapped ions containing heavy exotic nuclei. We consider the symmetric top cation ^{225}RaOCH_{3}^{+} as a prototypical and candidate platform for performing sensitive nuclear Schiff measurements and characterize in detail its internal structure using relativistic abinitio methods. The combination of enhancements from a deformed nucleus, large polarizability, and unique molecular structure make this molecule a promising platform to search for fundamental symmetry violation even with a single trapped ion.

Gadolinium as an accelerator for reaching thermal equilibrium and its influence on the ground state of Dy2GdN@C80 single-molecule magnets

Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that the Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes faster equilibration in Dy2GdN@C80. This sheds light on the importance of the angular momentum balance in magnetic relaxation.

Schiff moments of Hg isotopes in the nuclear shell model

Existence of the permanent electric dipole moment of a fundamental particle implies violation of time reversal invariance. The electric dipole moment of a diamagnetic neutral atom is mainly induced by the nuclear Schiff moment. In this study the Schiff moment induced by the interaction which violates parity and time reversal invariance is calculated for the 199Hg nucleus in terms of the nuclear shell model.

Hydrogen Line Shapes in Plasmas with Large Magnetic Fields

We report on hydrogen line shape calculations in the presence of an external magnetic field, at conditions such that the quadratic Zeeman effect is important. The latter is described through a term proportional to B2 in the Hamiltonian, accounting for atomic diamagnetism. It provides a shift and an asymmetry on Lorentz triplets, and it leads to the occurrence of forbidden components. Motivated by investigations performed at the fifth edition of the Spectral Line Shape in Plasmas (SLSP5) code comparison workshop, we perform new calculations of hydrogen Lyman line profiles. Field values representative of magnetized white dwarf atmosphere conditions are taken. The calculations are done using a computer simulation technique, designed for Stark broadening modeling. A discussion of the results is done in the framework of plasma diagnostics.

Sensitivity of EDM experiments in paramagnetic atoms and molecules to hadronic CP violation

Experiments searching for the electric dipole moment (EDM) of the electron $d_e$ utilise atomic/molecular states with one or more uncompensated electron spins, and these paramagnetic systems have recently achieved remarkable sensitivity to $d_e$. If the source of $CP$ violation resides entirely in the hadronic sector, the two-photon exchange processes between electrons and the nucleus induce $CP$-odd semileptonic interactions, parametrised by the Wilson coefficient $C_{SP}$, and provide the dominant source of EDMs in paramagnetic systems instead of $d_e$. We evaluate the $C_{SP}$ coefficients induced by the leading hadronic sources of $CP$ violation, namely nucleon EDMs and $CP$-odd pion-nucleon couplings, by calculating the nucleon-number-enhanced $CP$-odd nuclear scalar polarisability, employing chiral perturbation theory at the nucleon level and the Fermi-gas model for the nucleus. This allows us to translate the ACME EDM limits from paramagnetic ThO into novel independent constraints on the QCD theta term $|\bar \theta| < 3 \times 10^{-8}$, proton EDM $|d_p| < 2 \times 10^{-23}\,e\,{\rm cm}$, isoscalar $CP$-odd pion-nucleon coupling $|\bar g^{(1)}_{\pi NN}| < 4 \times 10^{-10}$, and colour EDMs of quarks $|\tilde d_u - \tilde d_d| < 2 \times 10^{-24}\,{\rm cm}$. We note that further experimental progress with EDM experiments in paramagnetic systems may allow them to rival the sensitivity of EDM experiments with neutrons and diamagnetic atoms to these quantities.

Parity- and Time-Reversal-Violating Nuclear Forces

Parity-violating and time-reversal conserving (PVTC) and parity-violating and time-reversal-violating (PVTV) forces in nuclei form only a tiny component of the total interaction between nucleons. The study of these tiny forces can nevertheless be of extreme interest because they allow to obtain information on fundamental symmetries using nuclear systems. The PVTC interaction derives from the weak interaction between the quarks inside nucleons and nuclei and the study of PVTC effects opens a window on the quark-quark weak interaction. The PVTV interaction is sensitive to more exotic interactions at the fundamental level, in particular to strong CP violation in the Standard Model Lagrangian, or even to exotic phenomena predicted in various beyond-the-Standard-Model scenarios. The presence of these interactions can be revealed either by studying various asymmetries in polarized scattering of nuclear systems, or by measuring the presence of non-vanishing permanent electric dipole moments of nucleons, nuclei and diamagnetic atoms and molecules. In this contribution, we review the derivation of the nuclear PVTC and PVTV interactions within various frameworks. We focus in particular on the application of chiral effective field theory, which allows for a more strict connection with the fundamental interactions at the quark level. We investigate PVTC and PVTV effects induced by these potential on several few-nucleon observables, such as the longitudinal asymmetry in proton-proton scattering and radiative neutron-proton capture, and the electric dipole momentsof the deuteron and the trinucleon system.

Quantum-Assisted Measurement of Atomic Diamagnetism

An atom interferometer reaches a high enough sensitivity to measure the ground-state diamagnetism of single atoms.

New proof explores electric and magnetic fields in molecules

Researcher develops a unique approach to prove continuity equations for current and charge densities induced by static magnetic field and monochromatic plane waves in diamagnetic atoms and molecules.

Continuity equations for electron charge densities and current densities induced in molecules by electric and magnetic fields.

A series of relationships proving that the stationary current density JB(r), induced by a homogeneous time-independent magnetic field B in the electrons of diamagnetic atoms and molecules, is divergenceless are reported, assuming the conventional partition into diamagnetic and paramagnetic contributions and within the representations referred to as CTOCD (continuous translation of the origin of the current density). The continuity equations involving partial time derivatives of the dynamic polarization charge density ρ(1)(r, ω) and divergence of the current density J(1)(r, ω), induced in a molecule by a monochromatic plane wave of frequency ω, obtained by first-order time-dependent quantum mechanical perturbation theory, are investigated supposing that the wavefunctions of the ground and excited states are either real or complex. It is found that these continuity equations are satisfied by the exact eigenfunctions of a model Hamiltonian and by variationally optimal wavefunctions, for which hypervirial theorems are assumed to be valid. They are expected to hold only approximately in calculations using the algebraic approximation, with increasing accuracy for extended high-quality basis sets.

Mössbauer study of non-stoichiometric FeCr2S4 system

A partial spin transition stimulated by spontaneous symmetry breaking has been observed, for the first time, in the non-stoichiometric chalcogenide spinel FeCr2S4. A Fe2+ high spin - low spin transition HS-LS: S = 2 → S = 0 is detected below the Néel temperature TN in the magnetic subsystem corresponding to a part of the sample with deviations from stoichiometry. The fraction of diamagnetic Fe atoms increases with decreasing temperature.

Searches for Electric Dipole Moments—Overview of Status and New Experimental Efforts

Searches for permanent electric dipole moments (EDMs) of fundamental particles, atoms and molecules are promising experiments to constrain and potentially reveal beyond Standard Model (SM) physics. A non-zero EDM is a direct manifestation of time-reversal (T) violation, and, equivalently, violation of the combined operation of charge-conjugation (C) and parity inversion (P). Identifying new sources of CP violation can help to solve fundamental puzzles of the SM, e.g., the observed baryon-asymmetry in the Universe. Theoretical predictions for magnitudes of EDMs in the SM are many orders of magnitude below current experimental limits. However, many theories beyond the SM require larger EDMs. Experimental results, especially when combined in a global analysis, impose strong constraints on CP violating model parameters. Including an overview of EDM searches, I will focus on the future neutron EDM experiment at TRIUMF (Vancouver). For this effort, the TUCAN (TRIUMF Ultra Cold Advanced Neutron source) collaboration is aiming to build a strong, world leading source of ultra cold neutrons (UCN) based on a unique combination of a spallation target and a superfluid helium UCN converter. Another focus will be the search for an EDM of the diamagnetic atom 129 Xe using a 3 He comagnetometer and SQUID detection. The HeXeEDM collaboration has taken EDM data in 2017 and 2018 in the magnetically shielded room (BMSR-2) at PTB Berlin.

A new limit of the 129Xenon Electric Dipole Moment

We report on the first preliminary result of our 129Xe EDM measurement performed by the MIXed collaboration. The aim of this report is to demonstrate the feasibility of a new method to set limits on nuclear EDMs by investigating the EDM of the diamagnetic 129Xe atoms. In our setup, hyperpolarized 3He serves as a comagnetometer needed to suppress magnetic field fluctuations. The free induction decay of the two polarized spin species is directly measured by low noise DC SQUIDs, and the weighted phase difference extracted from these measurements is used to determine a preliminary upper limit on the 129Xe EDM.