Search

Single metallocene molecules act as sensitive spin detectors when decorating the probe of a scanning tunneling microscope (STM). However, the impact of the atomic-scale electrode details on the molecular spin state has remained elusive to date. Here, a nickelocene (Nc) STM junction is manipulated in an atomwise manner showing clearly the dependence of the spin excitation spectrum on the anchoring of Nc to Cu(111), a Cu monomer, and trimer. Moreover, while the spin state of the same Nc tip is a triplet with tunable spin excitation energies upon contacting the surface, it transitions to a Kondo-screened doublet on a Cu atom. Notably, the nontrivial magnetic exchange interaction of the molecular spin with the electron continuum of the substrate determines the spectral line shape of the spin excitations.

Triangulene nanographenes are open‐shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long‐sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl‐anthracene cyclic hexamer and the on‐surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π‐electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems. [ABSTRACT FROM AUTHOR]

Inelastic electron tunneling spectroscopy (IETS) based on scanning tunneling microscopy (STM) opens a new avenue for vibrational spectroscopy at single bond level. Since its birth, STM-IETS has been widely used for chemical identification and investigating the intra- and inter-molecular interactions as well as chemical reactions. In this review, we mainly focus on the new development and application of STM-IETS in the past decade. After introducing the basic theoretical background of IETS, we will discuss the recent advances of STM-IETS as vibrational spectroscopy and microspectroscopy, with emphasis on the ability of probing weak intermolecular interactions. The coupling of inelastic tunneling electrons to other elementary excitations, such as rotation, phonon, spin, plasmon, photon, etc., will be also briefly reviewed. In the end, we present a perspective for the future directions and challenges of STM-IETS. The goal of this review is to demonstrate the versatility of STM-IETS and inspire new applications in interdisciplinary fields.

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials.

The S = 1 / 2 kagome- and triangular-lattice Heisenberg antiferromagnets are investigated using the numerical exact diagonalization and the finite-size scaling analysis. The behaviour of the field derivative at zero magnetization is examined for both systems. The present result indicates that the spin excitation is gapless for each system. [ABSTRACT FROM AUTHOR]

Superconductivity in copper oxides emerges on doping holes or electrons into their Mott-insulating parent compounds. The spin excitations are thought to be the mediating glue for the pairing in superconductivity. Here the momentum and doping dependence of the dynamical spin response in the electron-doped cuprate superconductors is studied based on the kinetic-energy-driven superconducting mechanism. It is shown that the dispersion of the low-energy spin excitations changes strongly upon electron doping; however, the hour-glass-shaped dispersion of the low-energy spin excitations appeared in the hole-doped case is absent on the electron-doped side due to the electron-hole asymmetry. In particular, the commensurate resonance appears in the superconducting state with the resonance energy that correlates with the dome-shaped doping dependence of the superconducting gap. Moreover, the spectral weight and dispersion of the high-energy spin excitations in the superconducting state are comparable with those in the corresponding normal state, indicating that the high-energy spin excitations do not play an important part in the pair formation. [ABSTRACT FROM AUTHOR]

Spin excitation in poly(1,4-bis(2,2,6,6-tetramethyl-4-oxy-piperidyl-1-oxyl)-butadiin) (poly-BIPO), a quasi-one-dimensional organic ferromagnet, was investigated based on the extended Su-Schriffer-Heeger model by considering electron hopping and the spin correlation between the main chain and side radicals. The lattice, charge density, and spin density configurations of the single spin as well as spin domain excited states of the organic ferromagnet poly-BIPO were systematically studied. The side radical spin excitation gives rise to lattice distortion, charge density localization, and a spin density defect on the main chain. A peak induced by spin excitation is predicted to appear in the density of states of the organic ferromagnet poly-BIPO based on calculations for different spin electron states. These results expand knowledge on elementary excitation in organic materials and have significant implications for the design of spintronic devices. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on La 1.75 Sr 0.25 CuO 4 . We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at Q tet = ( 0.5 ± δ , 0.5 ) / ( 0.5 , 0.5 ± δ ) [1] . In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at Γ point Q tet = ( 0.5 , 0.5 ) in a constant energy spectrum at T = 50 K . The radius of the ring ( r = 0.109 ) is smaller than the incommensurability ( δ = 0.118 ) . This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the La 2- x Sr x CuO 4 system are inherently composed of these two kinds of excitations. [ABSTRACT FROM AUTHOR]

In this paper, the high-energy magnetic excitations in cuprate superconductors are studied based on the kinetic energy driven superconducting mechanism. The spin self-energy is evaluated explicitly in terms of the collective charge carrier modes in the particle-hole and particle-particle channels, and employed to calculate the dynamical spin structure factor. Our results show the existence of damped but well-defined dispersive spin excitations in the whole doping phase diagram. In particular, the charge carrier doping has a more modest effect on the high-energy spin excitations, and then the high-energy magnetic excitations retain roughly constant energy as a function of doping, with spectral weights and dispersion relations comparable to those found in the parent compound. [ABSTRACT FROM AUTHOR]

Superconductivity in cuprate superconductors occurs upon charge-carrier doping Mott insulators, where a central question is what mechanism causes the loss of electrical resistance below the superconducting (SC) transition temperature? In this paper, we attempt to summarize the basic idea of the kinetic-energy-driven SC mechanism in the description of superconductivity in cuprate superconductors. The mechanism of the kinetic-energy-driven superconductivity is purely electronic without phonons, where the charge-carrier pairing interaction in the particle-particle channel arises directly from the kinetic energy by the exchange of spin excitations in the higher powers of the doping concentration. This kinetic-energy-driven d-wave SC-state is controlled by both the SC gap and quasiparticle coherence, which leads to that the maximal SC transition temperature occurs around the optimal doping, and then decreases in both the underdoped and overdoped regimes. In particular, the same charge-carrier interaction mediated by spin excitations that induces the SC-state in the particle-particle channel also generates the normal-state pseudogap state in the particle-hole channel. The normal-state pseudogap crossover temperature is much larger than the SC transition temperature in the underdoped and optimally doped regimes, and then monotonically decreases upon the increase of doping, eventually disappearing together with superconductivity at the end of the SC dome. This kinetic-energy-driven SC mechanism also indicates that the strong electron correlation favors superconductivity, since the main ingredient is identified into a charge-carrier pairing mechanism not from the external degree of freedom such as the phonon but rather solely from the internal spin degree of freedom of the electron. The typical properties of cuprate superconductors discussed within the framework of the kinetic-energy-driven SC mechanism are also reviewed. [ABSTRACT FROM AUTHOR]

Composed of the three spiral magnetic vectors, the structure of skyrmion lattice (SkL) can be destructed by spin excitations in possibly two ways: one is to make decoherence of all the helices through the phase change of a certain spiral magnetic vector, and the other is to inhibit one or two spiral components while enhancing the others so that it becomes a magnetic structure of single or double magnetic vectors. Here, we present a micromagnetic study on the spin excitations of a two-dimensional SkL under the in-plane microwave magnetic field. By calculating the parameters describing the in-plane spin excitations mode, we find that the spin configuration tends to be an enhanced single-vector spiral magnetic structure due to the excitation modes under some specific frequencies so that the SkL will collapse to the topologically trivial state. Our results help to form a deeper understanding of the spin excitation in SkL under an ac magnetic field., (© 2022 IOP Publishing Ltd.)

Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Individual magnetic transition metal dopants in a solid host usually exhibit relatively small spin excitation energies of a few meV. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy (IETS) techniques, we have observed a high spin excitation energy around 36 meV for an individual Co substitutional dopant in ultrathin NaCl films. In contrast, the Cr dopant in the NaCl film shows much lower spin excitation energy around 2.5 meV. Electronic multiplet calculations combined with first-principles calculations confirm the spin excitation induced IETS, and quantitatively reveal the out-of-plane magnetic anisotropies for both Co and Cr. They also allow reproducing the experimentally observed redshift in the spin excitations of Co dimers and ascribe it to a charge and geometry redistribution., (Creative Commons Attribution license.)

Starting from a two-orbital model and based on the random phase approximation, spin excitations in the superconducting state of the newly discovered BiS superconductors with three possible pairing symmetries are studied theoretically. It is found that the spin response is uniquely determined by the pairing symmetry. Possible spin resonance excitations may occur at an incommensurate momentum about (0.7 π,0.7 π) for the d-wave symmetry, while the transverse spin excitation near (0,0) is enhanced for the p-wave symmetry and no spin resonance signature is seen for the s-wave pairing symmetry. These distinct features may be used for probing or determining the pairing symmetry in this newly discovered compound. [ABSTRACT FROM AUTHOR]

Highlights: [•] Designed and fabricated an efficient resonator to obtain strong excitation. [•] Obtained a Rabi frequency of 210MHz at 1W of pulse power (π/2 pulse=1.2ns). [•] Proposed an effective and flexible coupling method for stripline resonators. [ABSTRACT FROM AUTHOR]

Abstract: Spin excitations of overdoped La2−x Sr x CuO4 (0.25⩽ x ⩽0.30) have been studied by neutron scattering utilizing triple-axis and time-of-flight spectrometers. Low-energy excitation spectra (ω ⩽10meV) for all of the superconducting samples show a maximum around ω =6meV with a maximum value of dynamic spin susceptibility χ″(ω) that decreases linearly with T c as doping increases. The magnetic scattering cross section finally disappears at x =0.30, coincident with the disappearance of bulk superconductivity. Time-of-flight measurements for x =0.25 and 0.30 show markedly suppressed magnetic scattering intensities at intermediate energies (20⩽ ω ⩽80meV) in contrast to those of the stripe-ordered La1.875Ba0.125CuO4, which shows large spectral weight near the saddle point of the “hour-glass” shape dispersion. These facts imply a cooperative correlation between the dynamic incommensurate state and the superconductivity. [Copyright &y& Elsevier]

A review is given on neutron scattering study of Zn-doping effects on low-energy spin excitations in optimally hole-doped La2−xSrxCuO4. As Zn-impurities increase, energy spectra of incommensurate spin excitations show a dramatic change from a well defined “spin gap” state to a gap-less excitation with static antiferromagnetic (AF) spin correlations. This modification of the gap structure can be understood as not simply reduction of the gap energy but a development of the Zn-induced in-gap excitation, which becomes more static with increasing Zn. An inhomogeneous mixed state of the in-gap spin excitation and the superconductivity is discussed with referring to the swiss cheese model. [Copyright &y& Elsevier]

Bond-resolved STM, on-surface synthesis, open-shell, spin excitation, triangulene Keywords: bond-resolved STM; on-surface synthesis; open-shell; spin excitation; triangulene EN bond-resolved STM on-surface synthesis open-shell spin excitation triangulene 1 1 1 11/17/21 20211122 NES 211122 B Macrocycles b In their Communication on page 25224, Thomas Frederiksen, Jose Ignacio Pascual, Diego Peña et al. report the on-surface synthesis and collective spin excitations of a triangulene-based nanostar. Frontispiece: On-Surface Synthesis and Collective Spin Excitations of a Triangulene-Based Nanostar. [Extracted from the article]

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials. [ABSTRACT FROM AUTHOR]

Abstract: We report the results of high-field multi-frequency ESR experiment on the Heisenberg antiferromagnetic chain for the fields up to about 55T and the frequencies up to about 2THz. We have found that excitation branches above the critical field where the energy gap closes change into one branch around 15T which becomes close to the paramagnetic line at high fields. The branch above 15T fits well the conventional antiferromagnetic resonance mode with easy planar anisotropy. We compare the results with those in a weakly coupled antiferromagnetic dimer compound and discuss the origin of the branches observed above . [Copyright &y& Elsevier]

We report on the fabrication and transport characterization of atomically precise single-molecule devices consisting of a magnetic porphyrin covalently wired by graphene nanoribbon electrodes. The tip of a scanning tunneling microscope was utilized to contact the end of a GNR-porphyrin-GNR hybrid system and create a molecular bridge between the tip and sample for transport measurements. Electrons tunneling through the suspended molecular heterostructure excited the spin multiplet of the magnetic porphyrin. The detachment of certain spin centers from the surface shifted their spin-carrying orbitals away from an on-surface mixed-valence configuration, recovering its original spin state. The existence of spin-polarized resonances in the free-standing systems and their electrical addressability is the fundamental step in the utilization of carbon-based materials as functional molecular spintronics systems.

Magnetic excitations of La1.95Sr0.05CuO4 were investigated using pulsed neutron inelastic scattering over a wide range of energy up to 300 meV. In contrast to the optimally doped superconductor the dynamical magnetic susceptibility χ″(ω) around (π,π) in the spin-glass phase monotonically decreases with increasing ω and nearly saturates beyond ∼50 meV. We found that the energy dependence of the q-position in the latter energy region is ascribed to a two-dimensional spin-wave dispersion relation with the nearest neighbor interaction J of 108±6 meV, which is smaller by ∼20% than that of La2CuO4. [Copyright &y& Elsevier]

The inelastic portion of the tunnel current through an individual magnetic atom grants unique access to read out and change the atom's spin state, but it also provides a path for spontaneous relaxation and decoherence. Controlled closure of the inelastic channel would allow for the latter to be switched off at will, paving the way to coherent spin manipulation in single atoms. Here, we demonstrate complete closure of the inelastic channels for both spin and orbital transitions due to a controlled geometric modification of the atom's environment, using scanning tunneling microscopy (STM). The observed suppression of the excitation signal, which occurs for Co atoms assembled into chains on a Cu2N substrate, indicates a structural transition affecting the dz(2) orbital, effectively cutting off the STM tip from the spin-flip cotunneling path.

The magnetism of single atoms and molecules is governed by the atomic scale environment. In general, the reduced symmetry of the surrounding splits the d states and aligns the magnetic moment along certain favorable directions. Here, we show that we can reversibly modify the magnetocrystalline anisotropy by manipulating the environment of single iron(II) porphyrin molecules adsorbed on Pb(111) with the tip of a scanning tunneling microscope. When we decrease the tip-molecule distance, we first observe a small increase followed by an exponential decrease of the axial anisotropy on the molecules. This is in contrast to the monotonous increase observed earlier for the same molecule with an additional axial Cl ligand ( Nat. Phys. 2013 , 9 , 765 ). We ascribe the changes in the anisotropy of both species to a deformation of the molecules in the presence of the attractive force of the tip, which leads to a change in the d level alignment. These experiments demonstrate the feasibility of a precise tuning of the magnetic anisotropy of an individual molecule by mechanical control.

Abstract: The spin excitations in the LaFeAsO1− x F x system have been studied by inelastic neutron scattering measurements with powder samples. In the parent compound, the spin excitation was observed as a magnetic rod at (π, π, l) in the downfolded tetragonal Brillouin zone. It persisted even in the tetragonal phase at T =280K. In the superconducting compounds with x =0.057 and 0.082, the spin excitations developed below the superconducting transition temperatures up to the same order of magnitude as that in the parent compound, and they were peaked at about 11meV. The spin excitation, however, almost disappeared in an overdoped compound with x =0.158, which exhibited only low temperature superconductivity below 7K. These results indicate that the present superconductivity intimately correlates with the spin fluctuation possibly in relation to the nesting condition between the Fermi surfaces at Γ and M points. [ABSTRACT FROM AUTHOR]