Orbital Excitations Research Articles

Orbital dynamics during an ultrafast insulator to metal transition

Phase transitions driven by ultrashort laser pulses have attracted interest both for understanding the fundamental physics of phase transitions and for potential new data storage or device applications. In many cases these transitions involve transient states that are different from those seen in equilibrium. To understand the microscopic properties of these states, it is useful to develop elementally selective probing techniques that operate in the time domain. Here we show fs-time-resolved measurements of V Ledge Resonant Inelastic X-Ray Scattering (RIXS) from the insulating phase of the Mott- Hubbard material V2O3 after ultrafast laser excitation. The probed orbital excitations within the d-shell of the V ion show a sub-ps time response, which evolve at later times to a state that appears electronically indistinguishable from the high-temperature metallic state. Our results demonstrate the potential for RIXS spectroscopy to study the ultrafast orbital dynamics in strongly correlated materials.

Anisotropic effect of a magnetic field on the neutron spin resonance in FeSe.

We use inelastic neutron scattering to study the effect of a magnetic field on the neutron spin resonance (E r = 3.6 meV) of superconducting FeSe (T c = 9 K). While a field aligned along the in-plane direction broadens and suppresses the resonance, a c-axis aligned field does so much more efficiently, consistent with the anisotropic field-induced suppression of the superfluid density from the heat capacity measurements. These results suggest that the resonance in FeSe is associated with the superconducting electrons arising from orbital selective quasiparticle excitations between the hole and electron Fermi surfaces.

Can the state Y(4626) be a P -wave tetraquark state [cs][c¯s¯] ?

Stimulated by the state $Y(4626)$ recently reported by Belle Collaboration, we utilize a multiquark color flux-tube model with a multibody confinement potential and one-glue-exchange interaction to make an exhaustive investigation on the diquark-antidiquark state $[cs][\bar{c}\bar{s}]$. Numerical results indicate that the appearance of the states $[cs][\bar{c}\bar{s}]$ like a dumb-bell, the larger the orbital excitation $L$, the more distinguished the shape. The mixing of the color configurations $\left[[cs]_{\bar{\mathbf{3}}_c}[\bar{c}\bar{s}]_{\mathbf{3}_c}\right]_{\mathbf{1}}$ and $\left[[cs]_{\mathbf{6}_c}[\bar{c}\bar{s}]_{\bar{\mathbf{6}}_c}\right]_{\mathbf{1}}$ in the ground states is strong while the color configuration $\left[[cs]_{\bar{\mathbf{3}}_c}[\bar{c}\bar{s}]_{\mathbf{3}_c}\right]_{\mathbf{1}}$ is absolutely predominant in the excited states. The main component of the state $Y(4626)$ can be interpreted as a $P$-wave state $[cs][\bar{c}\bar{s}]$. Its hidden-bottom partner is predicted in the model calculation. The states $X(4140)$, $X(4274)$, $X(4350)$, $X(4500)$ and $X(4700)$ are also discussed.

Shell model description of the core excited level structure of $$^{89}$$Sr nucleus and systematic features of the $$N=51$$ odd-A isotones

Shell-model calculations are performed using NuShellX code in the model space $$\pi $$($$f_{5/2}$$, $$p_{3/2}$$, $$p_{1/2}$$, $$g_{9/2}$$) $$\otimes $$ $$\nu $$($$g_{9/2}$$, $$g_{7/2}$$, $$d_{5/2}$$, $$h_{11/2}$$), which probe the proton core excitation from the interior of $$Z=38$$ semiclosed shell and neutron core excitation from the interior of $$N=56$$ semiclosed shell for the level structure of $$^{89}$$Sr. Our calculations show that the excitation of a single $$d_{5/2}$$ neutron across $$N=56$$ semiclosed shell into the $$h_{11/2}$$ orbit should have great effects on the excited states of $$^{89}$$Sr. In addition, the systematic features of proton core excitation across $$Z=38$$ semiclosed shell into the $$g_{9/2}$$ orbit and neutron core excitation across $$N=56$$ semiclosed shell into the $$g_{7/2}$$, $$s_{1/2}$$, $$d_{3/2}$$, $$h_{11/2}$$ orbits in $$N=51$$ isotones are discussed.

Two-dimensional orbital Hall insulators

The orbital-Hall effect (OHE), similarly to the spin-Hall effect (SHE), refers to the creation of a transverse flow of orbital angular momentum that is induced by a longitudinally applied electric field. For systems in which the spin-orbit coupling (SOC) is sizeable, the orbital and spin angular momentum degrees of freedom are coupled, and an interrelationship between charge, spin and orbital angular momentum excitations is naturally established. The OHE has been explored mostly in metallic systems, where it can be quite strong. However, several of its features remain unexplored in two-dimensional (2D) materials. Here, we investigate the role of orbital textures for the OHE displayed by multi-orbital 2D materials. We predict the appearance of a rather large orbital Hall effect in these systems both in their metallic and insulating phases. In some cases, the orbital Hall currents are larger than the spin Hall ones, and their use as information carriers widens the development possibilities of novel spin-orbitronic devices.

Coherent spin control of s-, p-, d- and f-electrons in a silicon quantum dot

Once the periodic properties of elements were unveiled, chemical behaviour could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in semiconductor materials disrupt this analogy, so real devices seldom display a systematic many-electron arrangement. We demonstrate here an electrostatically confined quantum dot that reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. Various fillings containing a single valence electron—namely 1, 5, 13 and 25 electrons—are found to be potential qubits. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR), leading to faster Rabi rotations and higher fidelity single qubit gates at higher shell states. We investigate the impact of orbital excitations on single qubits as a function of the dot deformation and exploit it for faster qubit control.

Spin and orbital excitations through the metal-to-insulator transition in Cd2Os2O7 probed with high-resolution resonant inelastic x-ray scattering

High-resolution resonant inelastic x-ray scattering (RIXS) measurements ($\Delta$E = 46 meV) have been performed on Cd$_2$Os$_2$O$_7$ through the metal-to-insulator transition (MIT). A magnetic excitation at 125 meV evolves continuously through the MIT, in agreement with recent Raman scattering results, and provides further confirmation for an all-in, all-out magnetic ground state. Asymmetry of this feature is likely a result of coupling between the electronic and magnetic degrees of freedom. We also observe a broad continuum of interband excitations centered at 0.3 eV energy loss. This is indicative of significant hybridization between Os 5$d$ and O 2$p$ states, and concurrent itinerant nature of the system. In turn, this suggests a possible break down of the free-ion model for Cd$_2$Os$_2$O$_7$.

Excitation of tumbling in Phobos and Deimos

Mass–spring model simulations are used to investigate past spin states of a viscoelastic Phobos and Deimos. From an initially tidally locked state, we find crossing of a spin–orbit resonance with Mars or a mean motion resonance with each other does not excite tumbling in Phobos or Deimos. However, once tumbling our simulations show that these moons can remain so for an extended period and during this time their orbital eccentricity can be substantially reduced. We attribute the tendency for simulations of an initially tumbling viscoelastic body to drop into spin-synchronous state at very low eccentricity to the insensitivity of the tumbling chaotic zone volume to eccentricity. After a tumbling body enters the spin synchronous resonance, it can exhibit long lived non-principal axis rotation and this too can prolong the period of time with enhanced tidally generated energy dissipation. The low orbital eccentricities of Phobos and Deimos could in part be due to spin excitation by nearly catastrophic impacts rather than tidal evolution following orbital resonance excitation.

Structure and excitation characteristics of C<sub>5</sub>F<sub>10</sub>O under external electric field based on density functional theory

In this paper, we use the density functional theory (B3LYP) method with 6-311g(d) basis sets to optimize the molecular structure of C<sub>5</sub>F<sub>10</sub>O and obtain the stable structure of its ground state. On this basis, the geometric characteristics, energy, frontier orbital energy levels, and infrared spectra of C<sub>5</sub>F<sub>10</sub>O under the different external electric fields (from 0 to 0.03 a.u., 1 a.u. = 5.142 × 10<sup>11</sup> V/m) are studied by the same method. Under the same basis sets, the orbital composition and excitation characteristics of C<sub>5</sub>F<sub>10</sub>O are calculated and analyzed by the TD-DFT method. The conclusions show that as the electric field increases, the bond energy of 5C—15F and 4C=16O gradually decrease, their bond lengths increase. The charge of 13F atoms changes fastest, and it is easier to lose electrons under the action of electric field force. The potential energy of the molecule increases, and the stability gradually decreases. The energy gap <i>E</i><sub>G</sub> value continuously decreases, and the molecules are more likely to be excited to participate in the chemical reaction. In the infrared spectrum, four absorption peaks are blue-shifted, and four absorption peaks are red-shifted. The excitation characteristics of the first 8 singlet excited states of the C<sub>5</sub>F<sub>10</sub>O are identified by the hole-electron analysis method. The excitation energy of the first excited state increases slightly, and the wavelength decreases, and blue shift occurs. The excitation energy values of the other excited states decrease, their wavelengths increase, and red shifts occur. Because the electrons in C<sub>5</sub>F<sub>10</sub>O become easier to excite, the stability of the system is lower.

High-resolution resonant inelastic x-ray scattering study of the electron-phonon coupling in honeycomb α−Li2IrO3

The excitations in honeycomb $\alpha$-Li$_2$IrO$_3$ have been investigated with high-resolution resonant inelastic x-ray scattering (RIXS) at the O K edge. The low-energy response is dominated by a fully resolved ladder of excitations, which we interpret as being due to multi-phonon processes in the presence of strong electron-phonon coupling (EPC). At higher energies, the orbital excitations are shown to be dressed by phonons. The high quality of the data permits a quantitative test of the analytical model for the RIXS cross-section, which has been proposed to describe EPC in transition metal oxides (TMOs). We find that the magnitude of the EPC is comparable to that found for a range of 3d TMOs. This indicates that EPC may be of equal importance in determining the phenomenology displayed by corresponding 5d based systems.

Secular resonance sweeping and orbital excitation in decaying disks

We revisit the problem of secular resonance sweeping during the dissipation of a protoplanetary disk and its possible role in exciting the orbits of primordial asteroids, in the light of recent models of solar system evolution. We develop an integrator that incorporates the gravitational effect of a uniformly (or not) depleting, axisymmetric disk with arbitrary surface density profile; its performance is verified by analytical calculations. The secular response of fictitious asteroids, under perturbations from Jupiter, Saturn and a decaying disk, is thoroughly studied. Note that the existence of a symmetry plane induced by the disk, lifts the inherent degeneracy of the two-planet system, such that the '$s_5$' nodal frequency can also play a major role. We examine different resonant configurations for the planets (2:1, 3:2, 5:3), disk models and depletion scenarios. For every case we compute the corresponding time paths of secular resonances, which show when and where resonance crossing occurs. The excitation of asteroids, particularly in inclination, is studied in the various models and compared to analytical estimates. We find that inclination excitation in excess of $\sim 10^{\circ}$ is possible in the asteroid belt, but the nearly uniform spread of $\Delta i\sim 20^{\circ}$ observed calls for the combined action of secular resonance sweeping with other mechanisms (e.g. scattering by Mars-sized embryos) that would be operating during terrestrial planet formation. Our results are also applicable to extrasolar planetary systems.

Spectrum of the uudc bar{c} hidden charm pentaquark with an SU(4) flavor-spin hyperfine interaction

We study a few of the lowest states of the pentaquark uudcoverline{c}, of positive and negative parity, in a constituent quark model with an SU(4) flavor-spin hyperfine interaction. For positive parity we introduce space wave functions of appropriate permutation symmetry with one unit of orbital angular momentum in the internal motion of the four-quark subsystem or an orbital excitation between the antiquark and the four quark subsystem which remains in the ground state. We show that the lowest positive parity states 1/2^+, 3/2^+ are provided by the first alternative and are located below the 1/2^- and the 1/2^+ states with all quarks in the ground state. We compare our results with the LHCb three narrow pentaquark structures reported in 2019.

Electronic landscape of the P-cluster of nitrogenase as revealed through many-electron quantum wavefunction simulations.

The electronic structure of the nitrogenase metal cofactors is central to nitrogen fixation. However, the P-cluster and FeMo cofactor, each containing eight Fe atoms, have eluded detailed characterization of their electronic properties. We report on the low-energy electronic states of the P-cluster in three oxidation states through exhaustive many-electron wavefunction simulations enabled by new theoretical methods. The energy scales of orbital and spin excitations overlap, yielding a dense spectrum with features that we trace to the underlying atomic states and recouplings. The clusters exist in superpositions of spin configurations with non-classical spin correlations, complicating interpretation of magnetic spectroscopies, whereas the charges are mostly localized from reorganization of the cluster and its surroundings. On oxidation, the opening of the P-cluster substantially increases the density of states, which is intriguing given its proposed role in electron transfer. These results demonstrate that many-electron simulations stand to provide new insights into the electronic structure of the nitrogenase cofactors.

2,3-di(2-furyl) quinoxaline bearing 3 -ethyl rhodanine and 1,3 indandione based heteroaromatic conjugated T-shaped push -pull chromophores: Design, synthesis, photophysical and non-linear optical investigations

The design, synthesis, computational, spectroscopic, and, the second and third order non-linear optical studies of a two new π-deficient cross-conjugated T-shaped push-pull molecules (QFR and QFI) consisting of 3-ethyl rhodanine and 1,3 indandione substituted with heterocyclic quinoxaline ring were synthesized by Knoevenagel condensation reaction of the precursor dialdehydes with active dye molecules were described in detail. In the as synthesized molecule, the electron donating thiophene moiety acts as an efficient π-bridge on either side to the quinoxaline core that permits good viability in fine-tuning the optical absorption spectrum with good solubility. The computational studies of these molecules show efficient intra molecular charge transfer (ICT) processes analyzed through their molecular orbital characteristics, excitation energy, absorption maxima, oscillator strength and Mulliken population analysis. The comparison study between the structures of these push-pull molecules were done by their photophysical characteristics including CIE coordinates; thermal characteristics, XRD studies and electrochemical analysis. The time-resolved fluorescence spectra with nanosecond time profile were measured to detect the delayed fluorescent performance of the push-pull molecules QFR and QFI. Hyper-Rayleigh scattering (HRS) in chloroform solution of varying concentrations, using a standard wavelength at 1064 nm was used to assess their first order hyperpolarizability. Optical non-linear property was again proved by open-aperture Z-scan technique investigated at 532 nm and the observed optical limiting behavior was originated from the reverse saturable absorption (RSA) process. The second and third order NLO studies reveals that 3-ethyl rhodanine substituted QFR molecule (β value from HRS, 84.64 × 10−30 esu and βeff from Z scan, 10 × 10−10 m/W) shows high non-linear optical properties and thermal stability compared with 1,3 indandione substituted QFI (β value from HRS, 48.00 × 10−30 esu and βeff value from Z scan, 2 × 10−10m/W).

Magnetic excitations in hole-doped Sr2IrO4 : Comparison with electron-doped cuprates

We have studied the evolution of magnetic and orbital excitations as a function of hole-doping in single crystal samples of Sr2Ir(1-x)Rh(x)O4 (0.07 < x < 0.42) using high resolution Ir L3-edge resonant inelastic x-ray scattering (RIXS). Within the antiferromagnetically ordered region of the phase diagram (x < 0.17) we observe highly dispersive magnon and spin-orbit exciton modes. Interestingly, both the magnon gap energy and the magnon bandwidth appear to increase as a function of doping, resulting in a hardening of the magnon mode with increasing hole doping. As a result, the observed spin dynamics of hole-doped iridates more closely resemble those of the electron-doped, rather than hole-doped, cuprates. Within the paramagnetic region of the phase diagram (0.17 < x < 0.42) the low-lying magnon mode disappears, and we find no evidence of spin fluctuations in this regime. In addition, we observe that the orbital excitations become essentially dispersionless in the paramagnetic phase, indicating that magnetic order plays a crucial role in the propagation of the spin-orbit exciton.

Study on semi-active control of running stability in the high-speed train under unsteady aerodynamic loads and track excitation

With the growing trend of higher running speed and lighter body weight in the high-speed train, the influences of fluctuating crosswind on running stability and safety are becoming more and more not negligible, especially under the combined action of unsteady aerodynamic loads and random orbital excitation. In order to investigate this problem, a vehicle dynamic model of with 42 degree of freedom is built, in which the major body, two bogies and eight wheels are involved. The unsteady aerodynamic loads under stochastically fluctuating crosswind are obtained based on Cooper theory and the harmonic superposition method, and the random excitation of the track is also taken into consideration. For the vertical vibration originated from the fluctuating crosswind and the random track spectrum, the skyhook damping and the magneto-rheological fuzzy semi-active control strategies are individually applied to suppress the vibrating amplitude and improve the running stability. It is indicated that the vertical vibration under the coupling influence of the unsteady aerodynamic loads and the random orbital excitation are significantly increased, and the vibrating amplitude can be effectively suppressed by both the two different control approaches. It is also shown that the index of running stability in the case of the fuzzy control is evidently better than the skyhook damping.

Optically controlled entangling gates in randomly doped silicon

Randomly-doped silicon has many competitive advantages for quantum computation; not only is it fast to fabricate but it could naturally contain high numbers of qubits and logic gates as a function of doping densities. We determine the densities of entangling gates in randomly doped silicon comprising two different dopant species. First, we define conditions and plot maps of the relative locations of the dopants necessary for them to form exchange interaction mediated entangling gates. Second, using nearest neighbour Poisson point process theory, we calculate the doping densities necessary for maximal densities of single and dual-species gates. We find agreement of our results with a Monte Carlo simulation, for which we present the algorithms, which handles multiple donor structures and scales optimally with the number of dopants and use it to extract donor structures not captured by our Poisson point process theory. Third, using the moving average cluster expansion technique, we make predictions for a proof of principle experiment demonstrating the control of one species by the orbital excitation of another. These combined approaches to density optimization in random distributions may be useful for other condensed matter systems as well as applications outside physics.

Orbital evolution of a circumbinary planet in a gaseous disk

Sub-Jupiter classed circumbinary planets discovered in close-in binary systems have orbits just beyond the dynamically unstable region, which is determined by the eccentricity and mass ratio of the host binary stars. These planets are assumed to have formed beyond the snow line and migrated to the current orbits rather than forming in situ. We propose a scenario in which a planet formed beyond the snow line and migrated to the inner edge of the circumbinary disk, which was within the unstable area, and then moved to the current orbit through outward transportation. This outward transportation is driven by the balance of orbital excitation of the central stars inside the gravitationally unstable region and damping by the gas-drag force. We carried out N-body simulations with a dissipating circumbinary protoplanetary disk for binary systems with different eccentricities and mass ratios. Planets are more likely to achieve a stable orbit just beyond the unstable region in less eccentric binary systems. This result is not as sensitive to mass ratio as it is to eccentricity. These dependencies are consistent with the data from observed binary systems hosting circumbinary planets. We find CBPs’ orbits close to the instability boundaries are explained by our orbital evolution scenario.

Spin preservation during THz orbital pumping of shallow donors in silicon

We investigate the spin relaxation under conditions of optical excitation between the Rydberg orbital states of phosphorus donor impurities in silicon. Here we show that the spin relaxation is less than a few percent, even after multiple excitation/relaxation cycles. The observed high level of spin preservation may be useful for readout cycling or in quantum information schemes where coupling of neighbor qubits is via orbital excitation.

Spin-Blockade Spectroscopy of Si / Si - Ge Quantum Dots

We implement a technique for measuring the singlet-triplet energy splitting responsible for spin-to-charge conversion in semiconductor quantum dots. This method, which requires fast, single-shot charge measurement, reliably extracts an energy in the limits of both large and small splittings. We perform this technique on an undoped, accumulation-mode Si/SiGe triple-quantum dot and find that the measured splitting varies smoothly as a function of confinement gate biases. Not only does this demonstration prove the value of having an $in~situ$ excited-state measurement technique as part of a standard tune-up procedure, it also suggests that in typical Si/SiGe quantum dot devices, spin-blockade can be limited by lateral orbital excitation energy rather than valley splitting.