Spin Coupling Research Articles

Designing Chiral Organometallic Nanosheets with Room-Temperature Multiferroicity and Topological Nodes.

Two-dimensional (2D) room-temperature chiral multiferroic and magnetic topological materials are essential for constructing functional spintronic devices, yet their number is extremely limited. Here, by using the chiral and polar HPP (HPP = 4-(3-hydroxypyridin-4-yl)pyridin-3-ol) as an organic linker and transition metals (TM = Cr, Mo, W) as nodes, we predict a class of 2D TM(HPP)2 organometallic nanosheets that incorporate homochirality, room-temperature magnetism, ferroelectricity, and topological nodes. The homochirality is introduced by chiral HPP linkers, and the change in structural chirality induces a topological phase transition of Weyl phonons. The room-temperature magnetism arises from the strong d-p spin coupling between TM cations and HPP doublet anions. The ferroelectricity is attributed to the breaking of spatial inversion symmetry in the lattice structure. Additionally, by adjusting the type of TMs, these nanosheets show rich and tunable band structures. Notably, all predicted materials are topologically nontrivial, featuring a quadratic nodal point around the Fermi level.

Uniaxial magnetic anisotropy and weak phonon–spin coupling of a single Ni atom bonded to iridium-doped graphene

We investigate the magnetism and vibrational mode of a single Ni atom bonded to iridium-doped graphene. It is found that the Ni atom exhibits a large magnetic anisotropy energy of 53 meV, and the magnetic anisotropy is perfectly uniaxial. There are no vibrational modes below 40 meV for the Ni atom, which disables the efficient coupling between the spin and phonon at the low magnetic field. The uniaxial magnetic anisotropy combining with the weak phonon–spin coupling effectively resists the quantum tunneling and spin flip, making the Ni atom a viable single atom magnet for information storage.

Modulating Magnetic Exchange, Spin Dynamics and Intermacrocyclic Interactions via Oxo-bridge in Dihemes Through Stepwise Oxidations

A bis-Fe(III)-µ-oxo-porphyrin dimer, where a rigid ethene-linker covalently connects the two porphyrin units, has been exploited to investigate the effect of intermacrocyclic interaction and spin coupling upon stepwise oxidations. The...

Spin Excitations of High Spin Iron(II) in Metal–Organic Chains on Metal and Superconductor

AbstractMany‐body interactions in metal–organic frameworks (MOFs) are fundamental for emergent quantum physics. Unlike their solution counterpart, magnetization at surfaces in low‐dimensional analogues is strongly influenced by magnetic anisotropy (MA) induced by the substrate and still not well understood. Here, on‐surface coordination chemistry is used to synthesize on Ag(111) and superconducting Pb(111) an iron‐based spin chain by using pyrene‐4,5,9,10‐tetraone (PTO) precursors as ligands. Using low‐temperature scanning probe microscopy, their structures and low‐energy spin excitations of coordinated Fe atoms are compared with high S = 2 spin‐state. Although the chain and coordination centers are identical on both substrates, the long‐range spin–spin coupling due to a superexchange through the ligand on Ag is not experimentally observed on Pb(111). This reduction of spin‐spin interactions on Pb in tunneling spectra is ascribed to the depletion of electronic states around the Fermi level of the Pb(111) superconductor as compared to silver.

Antiferromagnetic semiconductor nature in a GeS2 monolayer doped with Mn and Fe transition metals.

The absence of intrinsic magnetism in two-dimensional (2D) materials demands functionalization as necessary for broadening their applications. In this work, doping with transition metals (Mn and Fe) is proposed to modify the electronic and magnetic properties of a GeS2 monolayer. A pristine monolayer is an indirect gap semiconductor with an energy gap of 0.73(1.47) eV computed by using the PBE(HSE06) functional. Significant magnetism with a total magnetic moment of 1.18μB emerges in the GeS2 monolayer upon creating a single Ge vacancy, which is produced mainly by six nearest neighboring S atoms. In this case, the monolayer is metallized with S-px,y states responsible. Similarly, the magnetization of the GeS2 monolayer is also achieved by doping with Mn and Fe atoms with total magnetic moments of 3.00 and 3.78μB, respectively. The calculated band structures imply that the magnetic semiconductor nature with a spin-up/spin-down gap of 0.72/0.53 eV is induced by Mn impurity, while doping with Fe atoms leads to monolayer metallization. Being surrounded by more electronegative S atoms, Mn and Fe impurities lose charge amounts of 1.19 and 1.11e, respectively. Further investigations on spin coupling indicate the antiferromagnetic semiconductor nature in Mn- and Fe-doped systems, regardless of the distance between impurities. Our results provide important insights into the effects of doping into the GeS2 monolayer, which demonstrate that the doped systems hold promise for spintronic applications.

Interface engineering of van der Waals heterostructures towards energy-efficient quantum devices operating at high temperatures

Abstract Quantum devices, which rely on quantum mechanical effects for their operation, may offer advantages, such as reduced dimensions, increased speed, and energy efficiency, compared to conventional devices. However, quantum phenomena are typically observed only at cryogenic temperatures, which limits their practical applications. Two-dimensional materials and their van der Waals (vdW) heterostructures provide a promising platform for high-temperature quantum devices owing to their strong Coulomb interactions and/or spin-orbit coupling. In this review, we summarise recent research on emergent quantum phenomena in vdW heterostructures based on interlayer tunnelling and the coupling of charged particles and spins, including negative differential resistance, Josephson tunnelling, exciton condensation, and topological superconductivity. These are the underlying mechanisms of energy-efficient devices, including tunnel field-effect transistors, topological/superconducting transistors, and quantum computers. The natural homojunction within vdW layered materials offers clean interfaces and perfectly aligned structures for enhanced interlayer coupling. Twisted bilayers with small angles may also give rise to novel quantum effects. In addition, we highlight several proposed structures for achieving high-temperature Majorana zero modes, which are critical elements of topological quantum computing. This review is helpful for researchers working on interface engineering of vdW heterostructures towards energy-efficient quantum devices operating above the liquid nitrogen temperature.

Detection of spin current generated by the acoustic spin–rotation coupling mechanism via acoustic voltage

The method of combining surface acoustic waves (SAWs) with electrical detection has promoted the study of phonon–spin coupling and spintronics. Aiming at problems of difficult detection of DC voltage and unknown origin of spin current caused by SAW in ferromagnetic/light metal systems, we constructed the Ni/Cu/Ta on LiNbO3 substrate and measured acoustic voltages directly, which are used to analyze the spin current induced by SAW. By analyzing the angular dependence of acoustic voltages and estimating the maximum spin current, it is determined that acoustic voltages originate from the acoustic spin–rotation (ASR) coupling and the acoustic spin pumping (ASP) effects. The angular dependence shows that for the longitudinal voltage, the contribution of ASR to ASP is in the ratio of 3.22/3.77, while the transverse voltage is mainly contributed by the ASR. The maximum spin current due to ASR is 0.97 × 105 A/m2, while that due to ASP is 1.47 × 105 A/m2. This work provides ideas for the design of phonon–spin coupled devices.

Cavity-mediated iSWAP oscillations between distant spins

AbstractDirect interactions between quantum particles naturally fall off with distance. However, future quantum computing architectures are likely to require interaction mechanisms between qubits across a range of length scales. In this work, we demonstrate a coherent interaction between two semiconductor spin qubits 250 μm apart using a superconducting resonator. This separation is several orders of magnitude larger than for the commonly used direct interaction mechanisms in this platform. We operate the system in a regime in which the resonator mediates a spin–spin coupling through virtual photons. We report the anti-phase oscillations of the populations of the two spins with controllable frequency. The observations are consistent with iSWAP oscillations of the spin qubits, and suggest that entangling operations are possible in 10 ns. These results hold promise for scalable networks of spin qubit modules on a chip.

Fast generation of entanglement between coupled spins using optimization and deep learning methods

Coupled spins form composite quantum systems which play an important role in many quantum technology applications, with an essential task often being the efficient generation of entanglement between two constituent qubits. The simplest such system is a pair of spins-1/2 coupled with Ising interaction, and in previous works various quantum control methods such as adiabatic processes, shortcuts to adiabaticity and optimal control have been employed to quickly generate there one of the maximally entangled Bell states. In this study, we use machine learning and optimization methods to produce maximally entangled states in minimum time, with the Rabi frequency and the detuning used as bounded control functions. We do not target a specific maximally entangled state, like the preceding studies, but rather find the controls which maximize the concurrence, leading thus automatically the system to the closest such state in shorter time. By increasing the bounds of the control functions we observe that the corresponding optimally selected maximally entangled state also changes and the necessary time to reach it is reduced. The present work demonstrates also that machine learning and optimization offer efficient and flexible techniques for the fast generation of entanglement in coupled spin systems, and we plan to extent it to systems involving more spins, for example spin chains.

An explicitly magnetic modified embedded atom method formalism for coupled spin dynamics and molecular dynamics

Abstract In this paper, we augment the modified embedded atom method formalism to include magnetic spin-spin interactions for elements with a persistent magnetic moment. While previous spin coupling methods have been based on pair potentials, our Magnetic MEAM formalism, which we term MagMEAM, incorporates the many-body and angular effects of MEAM allowing for the strength of the magnetic interaction to vary with atomic environment. In particular, this allows potentials using this formalism to differentiate the magnetic interaction of different stable phases of magnetic elements such as the ferritic and austenitic phases of iron. This, in turn, allows for a more robust and realistic description of magnetism in polymorphic materials than was previously possible. The motivation for MagMEAM, including the insufficiency of magnetic pair potentials, is presented and the structure of the formalism is developed. A sample iron potential is developed using this formalism and shown to exceed the capabilities of existing magnetic pair potentials by simultaneously reproducing the magnetic energy of both martensite and austenite as well as the dynamic mechanical and magnetic properties of martensite. This newly designed formalism will allow for deeper explorations in the the complex interaction between different phases of polymorphic magnetic materials at the molecular dynamics scale.

Resonant spin dynamics of 2D electrons with strong Rashba and Zeeman couplings

Two-dimensional (2D) systems enable enhancing and diversifying the spin–orbit coupling of carriers, a key factor for better charge–spin conversion efficiencies in modern spintronic devices. Increasing 2D spin interactions also modifies dynamical spin-dependent properties of 2D materials, enabling to display resonant phenomena. In this work we focus on dynamical properties of the charge–spin conversion and analyze the resonant spin dynamics of 2D electrons upon strong spin–orbit coupling and Zeeman spin splittings, possibly exceeding the inverse relaxation times of electrons. We derive resonant frequencies and relaxation rates from the Bloch kinetic equations and examine how the trajectories of spin susceptibility poles change with variations in spin splittings and the relaxation time, paying special attention to the interplay between competing Rashba and Zeeman effect.

Superconductivity in the pressurized nickelate La3Ni2O7 in the vicinity of a BEC–BCS crossover

Ever since the discovery of high-temperature superconductivity in cuprates, gaining microscopic insights into the nature of pairing in strongly correlated systems has remained one of the greatest challenges in modern condensed matter physics. Following recent experiments reporting superconductivity in the bilayer nickelate La3Ni2O7 (LNO) with remarkably high critical temperatures of Tc = 80 K, it has been argued that the low-energy physics of LNO can be described by the strongly correlated, mixed-dimensional bilayer t–J model. Here we investigate this bilayer system and utilize density matrix renormalization group techniques to establish a thorough understanding of the model and the magnetically induced pairing through comparison to the perturbative limit of dominating inter-layer spin couplings. In particular, this allows us to explain appearing finite-size effects, firmly establishing the existence of long-range superconducting order in the thermodynamic limit. By analyzing binding energies, we predict a BEC–BCS crossover as a function of the Hamiltonian parameters. We find large binding energies of the order of the inter-layer coupling that suggest strikingly high critical temperatures of the Berezinskii–Kosterlitz–Thouless transition, raising the question of whether (mixD) bilayer superconductors possibly facilitate critical temperatures above room temperature.

Time-resolved photoelectron spectroscopy at surfaces

Light is a preeminent spectroscopic tool for investigating the electronic structure of surfaces. Time-resolved photoelectron spectroscopy has mainly been developed in the last 30 years. It is therefore not surprising that the topic was hardly mentioned in the issue on “The first thirty years” of surface science. In the second thirty years, however, we have seen tremendous progress in the development of time-resolved photoelectron spectroscopy on surfaces. Femtosecond light pulses and advanced photoelectron detection schemes are increasingly being used to study the electronic structure and dynamics of occupied and unoccupied electronic states and dynamic processes such as the energy and momentum relaxation of electrons, charge transfer at interfaces and collective processes such as plasmonic excitation and optical field screening. Using spin- and time-resolved photoelectron spectroscopy, we were able to study ultrafast spin dynamics, electron–magnon scattering and spin structures in magnetic and topological materials. Light also provides photon energy as well as electric and magnetic fields that can influence molecular surface processes to steer surface photochemistry and hot-electron-driven catalysis. In addition, we can consider light as a chemical reagent that can alter the properties of matter by creating non-equilibrium states and ultrafast phase transitions in correlated materials through the coupling of electrons, phonons and spins. Electric fields have also been used to temporarily change the electronic structure. This opened up new methods and areas such as high harmonic generation, light wave electronics and attosecond physics. This overview certainly cannot cover all these interesting topics. But also as a testimony to the cohesion and constructive exchange in our ultrafast community, a number of colleagues have come together to share their expertise and views on the very vital field of dynamics at surfaces. Following the introduction, the interested reader will find a list of contributions and a brief summary in Section 1.3.

Halogen-Dependent Circular Dichroism and Magneto-Photoluminescence Effects in Chiral 2D Lead Halide Perovskites.

Chiral lead halide perovskites (chiral LHPs) have emerged as one of the best candidates for opto-spintronics due to their large spin-orbit coupling (SOC) and unique chirality-induced spin selectivity (CISS) even in the absence of a magnetic field. Here, we report the impact of halide composition on circular dichroism (CD) and magneto-photoluminescence (PL) effects of chiral 2D LHPs (R/S-MBA)2PbBrxI4-x (MBA = C6H5CH2(CH3)NH3). By tuning the mixing ratio of Br/I halide anions, we find that (R/S-MBA)2PbBrxI4-x thin films exhibit tunable and wide wavelength range CD signals. Simultaneously, the main CD signals near the exciton absorption band gradually blue shift until they disappear. Moreover, the halogen-dependent negative magneto-PL effects of (R/S-MBA)2PbBrxI4-x thin films excited by left/right circularly polarized light can be detected at room temperature. We demonstrated that the halide composition can effectively modulate exciton splitting and chirality transfer in (R/S-MBA)2PbBrxI4-x owing to the chirality-induced SOC and crystalline structure transition, which lead to the adjustable CD signals. The interplay of Rashba-type band spin splitting and spin mixing among bright triplet exciton states is responsible for the halogen-dependent magneto-PL effect of chiral 2D LHPs. This study enables chiral 2D LHPs with CISS to be a new class of promising opto-spintronics materials for exploring high-performance spin-light-emitting diodes by halide engineering.

4hJCHOCH Spin Coupling in a Lewisx Trisaccharide as Evidence of Inter-Residue C-H···O Hydrogen Bonding in Aqueous Solution.

Prior studies of the solution conformation of the Lewisx (Lex) trisaccharide, αFuc-(1→3)[βGal-(1→4)]-βGlcNAc, suggest that nonclassical inter-residue C-H···O hydrogen bonding in aqueous solution contributes to the stabilization of its 3D structure and affects its biological properties. Experimental evidence for this hydrogen bond in aqueous solution has been reported in the form of a 4hJCHOCH NMR spin-coupling constant between C5'Fuc and H1″Gal measured by 2D NMR methods in unlabeled samples. A methyl glycoside of Lex (MeβLex) was prepared containing selective 13C-labeling at C5'Fuc, and the H1″Gal signal was examined in high-field 1H NMR spectra for evidence of splitting or line-broadening caused by the 13C at C5'Fuc. High-resolution 1H NMR spectra obtained at high field and at different temperatures using different FID processing parameters showed no resolved splitting of the H1″Gal signal or evidence of line-broadening. Spectral simulation showed that this splitting and/or line-broadening would be observable if the reported J-value (∼1.1 Hz) is correct. DFT calculations on MeβLex and a carbon analog (O5″Gal replaced by a CH2 group) gave very small and nearly identical calculated 4hJC5',H1″ values, suggesting that the coupling is essentially zero. DFT calculations also showed that an alternate inter-residue 3hJH5',H1″ is small. Based on NMR analyses and DFT calculations, we found that 4hJC5',H1″ in MeβLex has an upper limit of ∼0.4 Hz and that the value could be lower, possibly zero, calling into question its value as experimental proof of persistent nonclassical hydrogen bonding in aqueous solutions of MeβLex and related structures.

DNA Catalysis: Design, Function, and Optimization.

Catalytic DNA has gained significant attention in recent decades as a highly efficient and tunable catalyst, thanks to its flexible structures, exceptional specificity, and ease of optimization. Despite being composed of just four monomers, DNA's complex conformational intricacies enable a wide range of nuanced functions, including scaffolding, electrocatalysis, enantioselectivity, and mechano-electro spin coupling. DNA catalysts, ranging from traditional DNAzymes to innovative DNAzyme hybrids, highlight the remarkable potential of DNA in catalysis. Recent advancements in spectroscopic techniques have deepened our mechanistic understanding of catalytic DNA, paving the way for rational structural optimization. This review will summarize the latest studies on the performance and optimization of traditional DNAzymes and provide an in-depth analysis of DNAzyme hybrid catalysts and their unique and promising properties.

Helium roaming in excess electrons in C60F60 as dynamic quasi-Matryoshka dolls.

Multi-guest clathrates exhibit lots of functional characteristics owing to their unique structures, which herald beautiful application prospects, but their fundamental information is still scarce. Herein, we explore a type of (helium, excess electrons/EEs)-C60F60 co-clathrates with quasi-Matryoshka-doll structures using abinitio molecular dynamics simulation and reveal the EEs-entangled He roaming dynamics in C60F60 and its effect on the characteristics of clathrates. Perfluorination ensures that C60F60 possesses an extremely electropositive interior cavity. Its unique confinement effect can stabilize He as an extremely inert entity by noticeably enlarging the 1s-2s orbital gap and can also trap 1-2 EEs in its s-type interior orbital with extremely large binding energies. Co-inclusion of He and EEs in C60F60 exhibits inter-repulsive He⋯EEs entangling dynamics featuring quasi-Matryoshka-doll structures (He@EEs@C60F60). In this structure, EEs screen the attraction of cage-shell Cδ+ to He 1s2 electrons, thus inhibiting their stabilization and orbital expansion, while He conversely decreases the stability of EEs and redshifts their transition absorption. He can roam in the cavity, but its trajectory is impacted by EEs serving as a medium, and thus, the structures exhibit anormal dynamic variation of internuclear He⋯C spin coupling JHeC, which is manipulated by the EEs-entangled He roaming dynamics. JHeC and JHeC' present opposite distance dependences for the colinearly aligned C⋅⋅⋅He⋅⋅⊗⋅⋅⋅⋅⋅C' (⊗, the cage center). This work provides insights into the Matryoshka-doll structured He@EEs@C60F60 with He-EEs entangling dynamics and its modulation on EEs absorption and reveals the dynamic role of EEs in manipulating He-roaming and JHeC coupling properties for promising applications.

Spin relaxation dynamics with a continuous spin environment: The dissipaton equation of motion approach.

We investigate the quantum dynamics of a spin coupling to a bath of independent spins via the dissipaton equation of motion (DEOM) approach. The bath, characterized by a continuous spectral density function, is composed of spins that are independent level systems described by the su(2) Lie algebra, representing an environment with a large magnitude of anharmonicity. Based on the previous work by Suarez and Silbey [J. Chem. Phys. 95, 9115 (1991)] and by Makri [J. Chem. Phys. 111, 6164 (1999)] that the spin bath can be mapped to a Gaussian environment under its linear response limit, we use the time-domain Prony fitting decomposition scheme to the bare-bath time correlation function (TCF) given by the bosonic fluctuation-dissipation theorem to generate the exponential decay basis (or pseudo modes) for DEOM construction. The accuracy and efficiency of this strategy have been explored by a variety of numerical results. We envision that this work provides new insights into extending the hierarchical equations of motion and DEOM approach to certain types of anharmonic environments with arbitrary TCF or spectral density.

Disordered Heisenberg XYZ magnetic chains with exponential correlations: Localization and quantum state transfer

Our study investigates the Quantum State Transfer Protocol within a one-dimensional quantum Heisenberg spin chain model that features exponentially correlated disorder in the spin coupling distribution. We conducted extensive numerical simulations to explore how varying degrees of correlation impact the transfer of quantum states through this model of a quantum channel. Our results demonstrate that the extent of correlation significantly influences quantum communication along the channel. Specifically, we observed that in the strongly correlated regime, quantum communication remains largely unaffected even in large systems. These findings are interpreted in the context of the localization properties inherent to the disordered channel.

XIAM-NQ: Implementation of exact quadrupole coupling

In rotational spectroscopy, the nuclear quadrupole coupling of spins to the rotation of a molecule frequently leads to significant hyperfine splittings of spectral lines, complicating spectral analysis. This complexity increases further when internal rotation fine splittings, particularly from methyl groups, are also present. The XIAM program, recognized in the community for its ability to address methyl internal rotation and handle nuclear quadrupole coupling for a single nucleus, while neglecting off-diagonal matrix elements in the quantum number J, has now been enhanced. The updated version, XIAM-NQ, includes the previously omitted matrix elements, enabling an exact treatment of quadrupole coupling. This new version offers precise spectral fits with minimal fitting times, even for molecules containing bromine and iodine nuclei. The effectiveness of XIAM-NQ is demonstrated on o-halotoluenes and m-chlorotoluene.