Spin States Research Articles

Large Faraday Rotation in Pyrolysis Synthesized Carbon Dots

Pyrolysis of citric acid produced carbon dots on the 10 nm size scale, tunable by synthesis time. Magneto-optical spectroscopy revealed a size-dependent Faraday rotation. For particles with optimal synthesis time, the Verdet constant was measured as >300 times larger than that of water on a per-mass basis. Introducing ethylenediamine substrate as a nitrogen dopant in the synthesis resulted in a similar effect. These behaviors are indicative of extended sp2 networks in the particles. A strong wavelength dependence with largest rotation at the shortest measured wavelength of 405 nm was observed. This dependence is explained by a comparison with the theory of electron-photon interactions, which predicts an increase of the Verdet constant with 1/(ω02-ω2)2 for an angular frequency ω and an absorption line at ω0. The fitting of the analytical function to the measured Faraday rotation indicates a wavelength near 300 nm corresponding to the ω0, consistent with an extended electron delocalization. Nanomaterials with large magneto-optical effects have new proposed technological applications, such as in their use as magnetic field sensors. The Faraday rotation is related to spin-induced effects, foremost nuclear spin optical rotation, suggesting further applications of these materials for the optical readout of spin states in quantum information science.

Fractional Spinon Quasiparticles in Open-Shell Triangulene Spin-1/2 Chains.

The emergence of spinon quasiparticles, which carry spin but lack charge, is a hallmark of collective quantum phenomena in low-dimensional quantum spin systems. While the existence of spinons has been demonstrated through scattering spectroscopy in ensemble samples, real-space imaging of these quasiparticles within individual spin chains has remained elusive. In this study, we construct individual Heisenberg antiferromagnetic spin-1/2 chains using open-shell [2]triangulene molecules as building blocks. Each [2]triangulene unit, owing to its sublattice imbalance, hosts a net spin-1/2 in accordance with Lieb's theorem, and these spins are antiferromagnetically coupled within covalent chains with a coupling strength of J = 45 meV. Through scanning tunneling microscopy and spectroscopy, we probe the spin states, excitation gaps, and their spatial excitation weights within covalent spin chains of varying lengths with atomic precision. Our investigation reveals that the excitation gap decreases as the chain length increases, extrapolating to zero for long chains, consistent with Haldane's gapless prediction. Moreover, inelastic tunneling spectroscopy reveals an m-shaped energy dispersion characteristic of confined spinon quasiparticles in a one-dimensional quantum box. These findings establish a promising strategy for exploring the unique properties of excitation quasiparticles and their broad implications for quantum information.

Design for Telecom-Wavelength Quantum Emitters in Silicon Based on Alkali-Metal-Saturated Vacancy Complexes.

Defect emitters in silicon are promising contenders as building blocks of solid-state quantum repeaters and sensor networks. Here, we investigate a family of possible isoelectronic emitter defect complexes from a design standpoint. We show that the identification of key physical effects on quantum defect state localization can guide the search for telecom-wavelength emitters. We demonstrate this by performing first-principles calculations on the Q center, predicting its charged sodium variants possessing ideal emission wavelength near the lowest-loss telecom bands and ground state spin for possible spin-photon interface and nanoscale spin sensor applications yet to be explored in experiments.

Statistical model for quantum spin and photon number states

Statistical model for quantum spin and photon number states

Imaging of radio frequency magnetic field by multifrequency resonance

Abstract We present our results of a radio frequency (RF) imaging method in which microwave pulse errors in the field of view do not directly result in a deterioration of quantitative accuracy of the amplitude of the detected RF field by utilizing the multifrequency resonance. The amplitude of the RF field is transferred to the diamond nitrogen-vacancy (NV) center electron spin states, which are read out as light emission from the NV centers using a wide-field microscope at high throughput as an image with a pixel size of (1.65 μm)2. Importantly, our method simplifies the setup required for RF imaging, eliminating the need for high-power microwave pulses and offering a wide dynamic range for the detected RF field.

Electrochemical reduction for modulating spin state of nickel: A pathway to improved water and seawater oxidation

Electrochemical reduction for modulating spin state of nickel: A pathway to improved water and seawater oxidation

SU(N) symmetry with ultracold alkali dimers: Weak dependence of scattering properties on hyperfine state

We investigate the prospect of using ultracold alkali diatomic molecules to implement many-body quantum systems with SU(N) symmetry. Experimentally accessible molecules offer large N for both bosonic and fermionic systems, with both attractive and repulsive interactions. We carry out coupled-channel scattering calculations on pairs of NaK, NaRb, and NaCs molecules that are shielded from destructive collisions with static electric fields. We develop new methods to handle the very large basis sets required to include nuclear spins. We show that all the molecules studied have the properties required for SU(N) symmetry: the collisions are principally elastic, and the scattering lengths depend only weakly on the spin states of the molecules. The rates of spin-changing inelastic collisions are very low. We develop and test a semiclassical model of the spin dependence and find that it performs well. Published by the American Physical Society 2025

Modulation of Co spin state at Co3O4 crystalline-amorphous interfaces for CO oxidation and N2O decomposition

Modulation of electronic spin states in cobalt-based catalysts is an effective strategy for molecule activations. Crystalline-amorphous interfaces often exhibit unique catalytic properties due to disruptions of long-range order and alterations in electronic structure. However, the mechanisms of molecule activation and spin states at interfaces remain elusive. Herein, we present a Co3O4 spinel-based catalyst featuring crystalline-amorphous interfaces. Characterization analyses confirm that tetrahedral Co2+ is selectively etched from bulk spinel, forming amorphous CoO islands on the surface. The resultant symmetry breaking in the coordination field induces a reconstruction of the Co3+3 d orbitals, leading to high-spin states. In CO oxidation, the interface serves as novel active sites with a lower energy barrier, facilitated by lattice oxygen activation. In N2O decomposition, the interface promotes reassociation of dissociated oxygen through quantum spin exchange interactions. This work provides a straightforward approach to modulating the spin state of interfaces and elucidates their role in molecule activations.

A many-body quantum register for a spin qubit

Abstract Quantum networks require quantum nodes with coherent optical interfaces and several stationary qubits. In terms of optical properties, semiconductor quantum dots are highly compelling, but their adoption as quantum nodes has been impaired by the lack of auxiliary qubits. Here we demonstrate that the dense, always-present, nuclear spin ensemble surrounding a gallium arsenide quantum dot can be used as a functional quantum register. We prepared 13,000 host nuclear spins in a single many-body dark state that acts as a logical state of the register. A second logical state is defined as a single nuclear-magnon excitation, enabling controlled quantum-state transfer between an electron spin qubit in the quantum dot and the nuclear magnonic register. Using SWAP gates, we implemented a full write–store–retrieve-read-out protocol with 68.6(4)% raw overall fidelity and a storage time of 130(16) μs, which could be extended to 20 ms or beyond using dynamical decoupling techniques. Our work establishes how many-body physics can add functionality to quantum devices, in this case transforming quantum dots into multi-qubit quantum nodes with deterministic registers.

Complexes of d‐ and f‐metal Ions with Redox‐Active and Highly Symmetric Truxenone Ligand: Effect of Cations and Coordination on Distortions of Radical Anions and Singlet–Triplet Transition in Dianions

Truxenone (Tr) with high C3h symmetry forms crystalline radical anion and dianion salts. The {Bu3MeP+}(Tr·−)(1) and {Cp*2Co+)}(Tr·‐).2C6H4Cl2(2) show intense low‐energy absorption up to 2000nm. Calculations predict Jahn–Teller distortions for Tr·‐, which are enhanced by the asymmetric approach of cations to Tr·‐, leading to C=O bond length alternation and EPR signal asymmetry in 2. Two cesium ions form short contacts of 3.07–3.35Å with oxygen atoms of Tr2‐ in {Cryptand[2.2.2](Cs+)}2(Tr2‐)(3), linking the dianions into a 1D polymer. Calculations suggest a triplet state for the dianions, but the unsymmetric approach of Cs+ to the oxygen atoms of Tr2‐ stabilizes the singlet ground state. The triplet state is populated above 100K. An estimated singlet–triplet energy gap is 344±7K. Radical anions of Tr·‐ coordinate with one d‐ or f‐metal, forming {Cp*2Co+}{TbIII(TMHD)3×Tr}‐.1.5C7H8(4) and {Cp*2Co+}{MnII(acac)2×Tr}‐.2.4C6H4Cl2(5). Strong antiferromagnetic TbIII–Tr·‐ coupling (J =−7.6cm−1) aligns spins of TbIII and Tr·‐ antiparallel in 4. The χMT value of 3.32 emu×K/mol at 300K for 5 with high‐spin MnII is lower‐than‐expected. That indicates a spin state of S=2 owing to the antiparallel alignment of MnII and Tr·‐ spins. Strong MnII–Tr·‐ coupling arising from the spin density localization on the oxygen coordinated to MnII. Complexes with metals demonstrate low‐energy absorption with maxima at 1504–1740nm.

Spin State Modulation with Oxygen Vacancy Orientates C/N Intermediates for Urea Electrosynthesis of Ultrahigh Efficiency.

The co-electrolysis of CO2 and NO3 - to synthesize urea has become an effective pathway to alternate the conventional Bosch-Meiser process, while the complexity of C-/N-containing intermediates for C-N coupling results in the urea electrosynthesis of unsatisfactory efficiency. In this work, an electronic spin state modulation maneuver with oxygen vacancies (Ov) is unveiled to effectively meliorate the oriented generation of key intermediates *NH2 and *CO for C-N coupling, furnishing urea in ultrahigh yield of 2175.47µg mg-1h-1 and Faraday efficiency of 70.1%. Mechanistic studies expound that Ov can induce the conversion of the high-spin state Ni2+ (t2g 6eg 2) of Ni@CeO2-x to the low-spin state Ni3+ (t2g 6eg 1), which markedly enhances the hybridization degree of the Ni 3d and the N 2p orbitals of *NO, facilitating the selective formation of *NH2. Notably, the in situ generated *NH2 intermediates can serve as a localized proton donor to promote the electroreduction of CO2 on the adjacent site Ce3+-O to exclusively afford *CO, followed by C-N coupling of each other to efficiently synthesize urea. The strategy of tailored switching of the active site spin state provides a reliable reference to rectify the electronic structure of electrocatalysts for directional CO2 valorization.

Modulating Electronic Spin State of Perovskite Fluoride by Ni─F─Mn Bond Activating the Dynamic Site of Oxygen Reduction Reaction.

Establishing the relationship between catalytic performance and material structure is crucial for developing design principles for highly active catalysts. Herein, a type of perovskite fluoride, NH4MnF3, which owns strong-field coordination including fluorine and ammonia, is in situ grown on carbon nanotubes (CNTs) and used as a model structure to study and improve the intrinsic catalytic activity through heteroatom doping strategies. This approach optimizes spin-dependent orbital interactions to alter the charge transfer between the catalyst and reactants. As a result, the oxygen reduction reaction (ORR) activity of NH4MnF3 on CNTs is significantly enhanced by partial substitution of Mn sites with Ni, such as a half-wave potential (E1/2) of 0.86V and a limiting current density of 5.26mA cm-2, which are comparable to those of the commercial Pt/C catalysts. Experimental and theoretical calculations reveal that the introduction of Ni promotes lattice distortion, adjusts the electronic states of the active Mn centers, facilitates the transition from low-spin to intermediate-spin states, and shifts the d-band center closer to the Fermi level. This study establishes a novel approach for designing high-performance perovskite-based fluoride electrocatalysts by modulating spin states.

Thermally Induced FeII Spin Crossover Hybrid Complex incorporating para‐sulfocinnamic acid

Anion‐Driven Light‐Induced Spin Change (AD‐LISC) enables multifunctional materials to switch magnetic states with light, enhancing potential applications in data storage, sensors, and molecular electronics, by improving spin state control by integrating photoactive anions. In this study, we report the synthesis and characterization of new mononuclear FeII coordination complexes, [Fe(3‐bpp)2](psca)2∙solvent (1∙solvent), which includes para‐sulfocinnamic acid (psca) as a non‐coordinated anion. 57Fe Mössbauer spectroscopy and magnetic susceptibility measurements (SQUID) reveals a mixture of high‐spin and low‐spin states in 1 and 1∙2.5H2O, with a predominance of low‐spin sites at room temperature. The desolvated form 1 shows a gradual spin crossover behaviour centred around the room temperature region. Additionally, single crystal X‐ray diffraction, evaluated according to Schmidt's criteria for [2 + 2] photodimerization, revealed that 1∙X does not satisfy the spatial requirements for photodimerization; accordingly, no colour change was noticed upon UV light exposure.

Optimizing photocatalysis via electron spin control.

Solar-driven photocatalytic technology holds significant potential for addressing energy crisis and mitigating global warming, yet is limited by light absorption, charge separation, and surface reaction kinetics. The past several years has witnessed remarkable progress in optimizing photocatalysis via electron spin control. This approach enhances light absorption through energy band tuning, promotes charge separation by spin polarization, and improves surface reaction kinetics via strengthening surface interaction and increasing product selectivity. Nevertheless, the lack of a comprehensive and critical review on this topic is noteworthy. Herein, we provide a summary of the fundamentals of electron spin control and the techniques employed to scrutinize the electron spin state of active sites in photocatalysts. Subsequently, we highlight advanced strategies for manipulating electron spin, including doping design, defect engineering, magnetic field regulation, metal coordination modulation, chiral-induced spin selectivity, and combined strategies. Additionally, we review electron spin control-optimized photocatalytic processes, including photocatalytic water splitting, CO2 reduction, pollutant degradation, and N2 fixation, providing specific examples and detailed discussion on underlying mechanisms. Finally, we outline perspectives on further enhancing photocatalytic activity through electron spin manipulation. This review seeks to offer valuable insights to guide future research on electron spin control for improving photocatalytic applications.

Computational Investigation of the Role of Metal Center Identity in Cytochrome P450 Enzyme Model Reactivity.

Mononuclear Fe enzymes such as heme-containing cytochrome P450 enzymes catalyze a variety of C-H activation reactions under ambient conditions, and they represent an attractive platform for engineering reactivity through changes to the native enzyme. Using density functional theory, we study both native Fe and non-native group 8 (Ru, Os) and group 9 (Ir) metal centers in an active site model of P450. We quantify how changing the metal changes spin state preferences throughout the catalytic cycle. Our calculations reveal an intermediate-spin ground state for all Fe intermediates while the heavier metals prefer low-spin ground states across most intermediates in the reaction cycle. We also study the rate-determining hydrogen atom transfer (HAT) step and the subsequent rebound step. We observe comparable HAT barriers for Fe and Ru, a much higher barrier for Os, and the lowest HAT barrier for Ir. Rebound steps are barrierless for all metals, and the rebound intermediate for Fe is most significantly stabilized. Examination of ground spin states of all intermediates in the reaction cycle reveals spin-allowed pathways for the group 8 metals and spin-forbidden energetics for the group 9 Ir with potential two-state reactivity. Our work highlights the differences between the group 8 metals and the group 9 Ir, and it suggests that engineered P450 enzymes with Ru in particular result in improved enzyme reactivity toward C-H hydroxylation.

Exploring the equilibrium and non-equilibrium properties of a cooperative trinuclear spin-crossover chain: The role of elastic frustration.

Among the large family of spin-crossover (SCO) solids, recent investigations focused on polynuclear SCO materials, whose specific molecular configurations allow the presence of multi-step transitions and elastic frustration. In this contribution, we develop the first elastic modeling of thermal and dynamical properties of trinuclear SCO solids. For that, we study a finite SCO open chain constituted of successive elastically coupled trinuclear (A=B=C) blocks, in which each site (A, B, and C) may occupy two electronic configurations, namely, low-spin (LS) and high-spin (HS) states, accompanied with structural changes. Intra- and inter-molecular springs couple the sites inside and between trimers. The model also includes the change of length inside and between the trinuclear units subsequent to the spin states changes. First, we studied the mechanical relaxation of a LS chain initially prepared with HS distances, from which we dissected the dynamics of the atomic displacements for various strengths of intra- and inter-molecular elastic constants. Second, we investigated the thermal properties of the chain at equilibrium, which revealed the existence of a rich variety of behaviors, going from: gradual LS to HS transition to multiple spin transitions with the presence of self-organized spin state structures in the plateaus. The latter were identified as emerging from antagonist short- and long-range elastic interactions between intra- and inter-block size changes. The present model opens several possible extensions, among which are the cases of coupled non-linear trimer molecules as well as that of inter-chain interactions with block-block interactions, leading to unexpected hysteretic spin transitions.

Quantum magnetism of spin qubits in S = 1/2 Cu(II) systems in discrete complexes, chains, and metal-organic frameworks

In the last decade, S = 1/2 systems of Cu(II) complexes and Cu(II) ions in the solid state have been found to exhibit slow magnetic relaxations. The mechanism driving this magnetic behavior is different from that of high spin single-molecule magnets and that of bulk/nanoparticle magnets. This behavior is related to spin qubits and is considered to be a new type of quantum magnetism. This review focuses on the magnetic relaxation (τ), spin-lattice relaxation (T1), and spin-spin relaxation (T2 or Tm) of isolated Cu(II) complexes, Cu(II) 1D-chains, and Cu(II)-doped metal-organic frameworks. Although these properties have been well studied in isolated Cu(II) systems, studies on systems that exhibit magnetic interactions are still elusive. With the aim of progressing toward the entanglement of spin states and quantum computing using spin qubits, a greater number of studies on molecule-based spin qubits that exhibit magnetic interactions will be conducted and will be of increasing importance from now on.

RF Dielectric Permittivity Sensing of Molecular Spin State Switching Using a Tunnel Diode Oscillator

RF Dielectric Permittivity Sensing of Molecular Spin State Switching Using a Tunnel Diode Oscillator

Unveiling Aqueous Potassium-Ion Batteries with Prussian Blue Analogue Cathodes.

Aqueous rechargeable potassium-ion batteries have considerable advantages and potentials in the application of large-scale energy storage systems, owing to its high safety, abundant potassium resources, and environmental friendliness. However, the practical applications are fraught with numerous challenges. Identification of suitable cathode materials and potassium storage mechanisms are of great significance. Herein, an aqueous potassium-ion battery comprising Prussian blue analogs cathode (K1.15Fe[Fe(CN)6]·1.36H2O) and perylene-3,4,9,10-tetracarboxylic anode is designed, which delivers a high energy density of 52.0 Wh kg-1 and excellent cycling stability with high capacity retention of 84.5% after 4000 cycles. Importantly, a synergistic study of the relationships among crystal structure, spin state, kinetics, and electrochemical performances is thoroughly conducted. By employing in situ and ex situ characterizations, the potassium storage mechanism is comprehensively elucidated from multiple perspectives.

Quadruple-Q Skyrmion Crystal in Centrosymmetric Body-Centered Tetragonal Magnets

We conduct a numerical investigation into the stability of a quadruple-Q skyrmion crystal, a structure generated by the superposition of four spin density waves traveling in distinct directions within three-dimensional space, hosted on a centrosymmetric body-centered tetragonal lattice. Using simulated annealing applied to an effective spin model that includes momentum-resolved bilinear and biquadratic interactions, we construct a magnetic phase diagram spanning a broad range of model parameters. Our study finds that a quadruple-Q skyrmion crystal does not emerge within the phase diagram when varying the biquadratic interaction and external magnetic field. Instead, three distinct quadruple-Q states with topologically trivial spin textures are stabilized. However, we demonstrate that the quadruple-Q skyrmion crystal can become the ground state when an additional high-harmonic wave–vector interaction is considered. Depending on the magnitude of this interaction, we obtain two types of quadruple-Q skyrmion crystals exhibiting the skyrmion numbers of one and two. These findings highlight the emergence of diverse three-dimensional multiple-Q spin states in centrosymmetric body-centered tetragonal magnets.