Spin Exchange Interaction Research Articles

Enhanced Fulde-Ferrell-Larkin-Ovchinnikov and Sarma superfluid states near an orbital Feshbach resonance

We investigate the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and homogeneous Sarma superfluid states in alkaline-earth-like $^{173}$Yb atomic gases near an orbital Feshbach resonance at zero temperature with population imbalances in both the open and closed channels (or bands). We find that in homogeneous space by adjusting the open-channel Zeeman energy $h_o$, both the Sarma and Fulde-Ferrell superfluid states are greatly enhanced by the spin-exchange interaction while the closed-channel Zeeman energy $h_c$ remains small. In the presence of an external harmonic trap, the trapped gas features a shell structure of separated phases, where the Sarma phase leaves detectable valley structure in the columnar-integrated momentum distribution, and the Fulde-Ferrell state acquires enhanced spatial anisotropy. As both signatures can be easily detected in time-of-flight images, our findings are helpful to realize and detect the long-sought FFLO and Sarma superfluid states at the same time in experiments.

Frustrations and orderings in Ising chain with multiple interactions

The frustration properties of the Ising model on a one-dimensional monoatomic equidistant lattice are investigated taking into account the exchange interactions of atomic spins at the sites of the first (nearest), second (next-nearest) and third neighbors. The exact solution of the model was obtained using the Kramers–Wannier transfer matrix method. The types of magnetic ordering of the ground state of the model are determined, and a magnetic phase diagram is constructed. Criteria are formulated for the occurrence of magnetic frustrations in the presence of competition between the energies of exchange interactions. Non-zero entropy values in the ground state of the frustrated system were found.

Stripe and supersolid phases of spin–orbit coupled spin-2 Bose–Einstein condensates in an optical lattice

We study the ground-state phases of two-dimensional spin–orbit coupled spin-2 Bose–Einstein condensates in a one-dimensional spin-dependent optical lattice. Due to the competition among optical lattice, spin–orbit coupling and spin-exchange interaction, the exotic ground-state phases are found, i.e. three types of the stripe phases and three types of the supersolid phases. The spin-exchange interaction can adjust the direction of the stripe in the stripe phase and generate various vortex lattice structures in the supersolid phase, which shows that the spin-exchange interaction plays an important role in the formation of the stripe and supersolid phases of spin–orbit coupled spin-2 Bose–Einstein condensates in an optical lattice.

Spin-isospin Kondo effects for Σc and Σc* baryons and D¯ and D¯* mesons

We study the Kondo effect for a $\Sigma_{c}$ ($\Sigma_{c}^{\ast}$) baryon in nuclear matter. In terms of the spin and isospin ($\mathrm{SU}(2)_{\mathrm{spin}} \times \mathrm{SU}(2)_{\mathrm{isospin}}$) symmetry, the heavy-quark spin symmetry and the S-wave interaction, we provide the general form of the Lagrangian for a $\Sigma_{c}$ ($\Sigma_{c}^{\ast}$) baryon and a nucleon. We analyze the renormalization equation at the one-loop level, and find that the coexistence of spin exchange and isospin exchange magnifies the Kondo effect in comparison with the case where the spin-exchange interaction and the isospin-exchange interaction exist separately. We demonstrate that the solution exists for the ideal sets of the coupling constants, including the $\mathrm{SU}(4)$ symmetry as an extension of the $\mathrm{SU}(2)_{\mathrm{spin}} \times \mathrm{SU}(2)_{\mathrm{isospin}}$ symmetry. We also conduct a similar analysis for the Kondo effect of a $\bar{D}$ ($\bar{D}^{\ast}$) meson in nuclear matter. On the basis of the obtained result, we conjecture that there could exist a "mapping" from the heavy meson (baryon) in vacuum onto the heavy baryon (meson) in nuclear matter.

Noncollinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7

The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analysis and magnetic structure refinement, we demonstrate that Co2V2O7 possesses a complicated non-collinear magnetic ground state with Co moments mainly located in b-c plane and forming a non-collinear spin-chain-like structure along the c-axis. The ab initio calculations demonstrate that the non-collinear magnetic structure is more stable than various ferromagnetic states at low temperature. The non-collinear magnetic structure with canted up-up-down-down spin configuration is considered as the origin of magnetoelectric coupling in Co2V2O7 because the inequivalent exchange striction induced by the spin-exchange interaction between the neighboring spins is the driving force of ferroelectricity. Besides, it is found that the deviation of lattice parameters a and b is opposite below TN, while the lattice parameter c and stay almost constant below TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.

Hot-electron dynamics in quantum dots manipulated by spin-exchange Auger interactions.

The ability to effectively manipulate non-equilibrium 'hot' carriers could enable novel schemes for highly efficient energy harvesting and interconversion. In the case of semiconductor materials, realization of such hot-carrier schemes is complicated by extremely fast intraband cooling (picosecond to subpicosecond time scales) due to processes such as phonon emission. Here we show that using magnetically doped colloidal semiconductor quantum dots we can achieve extremely fast rates of spin-exchange processes that allow for 'uphill' energy transfer with an energy-gain rate that greatly exceeds the intraband cooling rate. This represents a dramatic departure from the usual situation where energy-dissipation via phonon emission outpaces energy gains due to standard Auger-type energy transfer at least by a factor of three. A highly favourable energy gain/loss rate ratio realized in magnetically doped quantum dots can enable effective schemes for capturing kinetic energy of hot, unrelaxed carriers via processes such as spin-exchange-mediated carrier multiplication and upconversion, hot-carrier extraction and electron photoemission.

Spin channel induced directional dependent spin exchange interactions between divacantly substituted Fe atoms in graphene

In this study, we investigate the isolated magnetic interactions between two identical Fe atoms divacantly-substituted into graphene. Using density functional theory, we simulated the electronic and magnetic properties for a supercell of graphene with spatial variation of the Fe atoms along either the armchair or zig-zag directions. Overall, we find that the exchange interaction between the two Fe atoms fluctuates from ferromagnetic to antiferromagnetic as a function of the spatial distance in the armchair direction. Given the induced magnetic moment and increased density of states at the Fermi level by the surrounding carbon atoms, we conclude that an RKKY-like interaction may characterize the exchange interactions between the Fe atoms. Furthermore, we examined the same interactions for Fe atoms along the zig-zag direction in graphene and found no evidence for an RKKY interaction as this system shows standard superexchange between the transition-metal impurities. Therefore, we determine that Fe-substituted graphene produces a directional-dependent spin interaction, which may provide stability to spintronic and multifunctional devices and applications for graphene.

Insights into magnetoelectric coupling mechanism of the room-temperature multiferroic Sr3Co2Fe24O41 from domain observation

The mechanism of a magnetoelectric coupling in a room-temperature multiferroic, $\mathrm{S}{\mathrm{r}}_{3}\mathrm{C}{\mathrm{o}}_{2}\mathrm{F}{\mathrm{e}}_{24}{\mathrm{O}}_{41}$, with the Z-type hexaferrite structure, is examined by three approaches: observations of domain structures and their field responses, measurements of magnetic-field effect on electric polarization, i.e., magnetoelectric effect, and phenomenological discussions on the interplay among coexisting order parameters. With use of a resonant soft x-ray microdiffraction technique, we visualized magnetic-field responses of two types of magnetic domains ascribed to ferrimagnetic and spiral components inherent in a transverse conical magnetic structure of the hexaferrite. A simultaneous inversion of these magnetic domains by a magnetic-field reversal was observed, meaning that the process of a magnetization reversal corresponds to a 180\ifmmode^\circ\else\textdegree\fi{} rotation of the cone axis. The reversal process of the magnetic structure, together with experimental results of the magnetoelectric effect, leads us to the conclusion that the magnetoelectricity in the Z-type hexaferrite originates mainly from the spin-dependent metal-ligand orbital hybridization, with minor contribution from the asymmetric spin-exchange interaction. Furthermore, such a mechanism is discussed by the symmetry analysis based on the Landau theory and is well described in terms of couplings among the coexisting order parameters included in the free energy. Thus, observations on field responses of multiple domains in multiferroics provide insights into underlying microscopic magnetoelectric coupling mechanisms.

Chiral molecules-ferromagnetic interfaces, an approach towards spin controlled interactions

Chiral symmetry is ubiquitous in Biology, Physics, and Chemistry. The biomolecules essential for life on Earth—such as deoxyribonucleic acid (DNA), sugars, and proteins—display homochirality that affects their function in biological processes. Ten years ago, it was discovered that electron transfer through chiral molecules depends on the direction of the electron spin, and more recently, it was shown that the charge displacement in chiral molecules creates transient spin polarization. Thus, the properties of ferromagnet/chiral molecule interfaces are affected by spin exchange interactions, via the overlap of the chiral molecule with the ferromagnet's spin wave function. This effect offers a mechanism for homochiral bias in Biology, which was previously unappreciated, and an approach to enantioselective chemistry and chiral separations, which is controlled by the electron spin.

Spin-exchange-induced exotic superfluids in a Bose-Fermi spinor mixture

We consider a mixture of spin-1/2 bosons and fermions, where only the bosons are subjected to the spin-orbit coupling induced by Raman beams. The fermions, although not directly coupled to the Raman lasers, acquire an effective spin-orbit coupling through the spin-exchange interaction between the two species. Our calculation shows that this is a promising way of obtaining spin-orbit coupled Fermi gas without Raman-induced heating, where the long-sought topological Fermi superfluids and topological bands can be realized. Conversely, we find that the presence of fermions not only provides a new way to create the supersolid stripe phase of the bosons, but more strikingly it can also greatly increase the spatial period of the bosonic density stripes, and hence makes this phase directly observable in the experiment. This system provides a new and practical platform to explore the physics of spin-orbit coupling, which possesses a dynamic nature through the interaction between the two species.

AFM-Based Spin-Exchange Microscopy Using Chiral Molecules.

Local magnetic imaging at nanoscale resolution is desirable for basic studies of magnetic materials and for magnetic logic and memories. However, such local imaging is hard to achieve by means of standard magnetic force microscopy. Other techniques require low temperatures, high vacuum, or strict limitations on the sample conditions. A simple and robust method is presented for locally resolved magnetic imaging based on short-range spin-exchange interactions that can be scaled down to atomic resolution. The presented method requires a conventional AFM tip functionalized with a chiral molecule. In proximity to the measured magnetic sample, charge redistribution in the chiral molecule leads to a transient spin state, caused by the chiral-induced spin-selectivity effect, followed by the exchange interaction with the imaged sample. While magnetic force microscopy imaging strongly depends on a large working distance, an accurate image is achieved using the molecular tip in proximity to the sample. The chiral molecules' spin-exchange interaction is found to be 150 meV. Using the tip with the adsorbed chiral molecules, two oppositely magnetized samples are characterized, and a magnetic imaging is performed. This method is simple to perform at room temperature and does not require high-vacuum conditions.

Synthesis, physico-chemical studies and biological evaluation of new metal complexes with some pyrazolone derivatives

A series of N-substituted-4-thiocarbamoyl-5-pyrazolone derivatives (HL1-HL4) is presented as chelating agents for complexation with Fe(III), Ni(II) and Cu(II) metal ions. The synthesized pyrazolone ligands and their newly metal complexes are characterized by different spectral and analytical methods such as UV–Vis, IR, 1H NMR, 13C NMR, ESR, MS, magnetic measurement, and TGA. The spectral data reveal that ligands coordinated to metal ions in a bidentate pattern via O & N atoms of the OH group at C(5) and thiocarbamoyl (–CSNHR) at C(4) of the pyrazolone ring. Also, the analytical data suggest the stoichiometries 2:3 (M:L) for both Cu(II) & Ni(II) complexes and 1:3 for Fe(III) complexes. Besides, the normal magnetic moments values for Fe(III) complexes confirm high spin octahedral structure while the diamagnetic nature of all Ni(II) complexes is consistent with square planar geometry. However, the subnormal magnetic values for Cu(II) complexes suggest the proposal of their binuclear structures. The ESR spectra of the Cu(II) complexes support the distorted square planar geometry with a considerably strong intradimeric spin-exchange interaction. Moreover, the anticancer, antibacterial and antifungal activities are screened. Among the synthesized compounds, HL4 ligand exhibits a significant broad spectrum of action against Gram-positive (S. aureus), Gram-negative bacteria (P. vulgaris), and antifungal potency against A. fumigatus &C. albicans in comparison with gentamicin and ketoconazole drug. Such potency of HL4 could be related to the insertion of the p-chloro in the phenyl group attached to the pharmacophoric thiocarbamoyl group at C(4). Furthermore, IC50 values of two Cu(II) complexes derived from HL2 and HL3 display nearly twofold or threefold more cytotoxicity impact against three cell lines (MCF-7, HCT116 and HepG-2) compared with cis-platin as positive control.

Quantum Transport of Rydberg Excitons with Synthetic Spin-Exchange Interactions

We present a scheme for engineering quantum transport dynamics of spin excitations in a chain of laser-dressed Rydberg atoms, mediated by synthetic spin exchange arising from diagonal van der Waals interaction. The dynamic tunability and long-range interaction feature of our scheme allows for the exploration of transport physics unattainable in conventional spin systems. As two concrete examples, we first demonstrate a topological exciton pumping protocol that facilitates quantized entanglement transfer, and second we discuss a highly nonlocal correlated transport phenomenon which persists even in the presence of dephasing. Unlike previous schemes, our proposal requires neither resonant dipole-dipole interaction nor off-diagonal van der Waals interaction. It can be readily implemented in existing experimental systems.

Atomic configuration, unusual lattice constant change, and tunable ferromagnetism in all-d-metal Heusler alloys Fe2CrV-FeCr2V

Abstract In this study, new all-d-metal Heusler alloys Fe50−xCr25+xV25 (x = 0–25) were investigated on the behaviors of atomic configuration, lattice constant change, and ferromagnetism from the aspects of theoretical calculations and experiments. The theoretical calculations found that both end-member compounds Fe50Cr25V25 (x = 0) and Cr50Fe25V25 (x = 25) prefer to crystallize in Hg2CuTi-type (space group: 216) structure rather than Cu2MnAl-type (space group: 225) one. During the whole substitution process, the structure of Fe50−xCr25+xV25 alloys remains Hg2CuTi-type structure, taking the path from 216 to 216, but with different degrees of BC-site disorder. Both the experimental and theoretical results reveal that the lattice constant increases first, and then abnormally decreases, showing a maximum at Cr40, due to the enhanced covalent d-d hybridizations between the transition metals. The magnetic moment and Curie temperature tuned by Cr substitution vary remarkably between 3.3 and 1.15 μB/f.u. and between 700 and 170 K, respectively, which indicates that the Cr substitution for Fe alters the spin polarizations and exchange interactions in the system. These results provide new insights into the atomic configuration, magnetism and bonding effect in all-d-metal Heusler alloys based on the d-d hybridizations.

Influence of cobalt doping on structure, optical and magnetic properties of spray pyrolysed nano structured ZnO films

Zn1-xCoxO (x = 0–10 at%) films were prepared using the spray pyrolysis method at 723 K on glass substrates. The structural and transport properties of Zn1-xCoxO deposits were studied using X-ray Diffraction(XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), UV-VIS Spectrophotometer and Vibrating Sample Magnetometer (VSM). XRD analysis confirmed a hexagonal wurtzite-type structure with a preferential orientation in the (0 0 2) plane, indicating Co2+ ion in the ZnO host matrix, and absence of secondary phase of the metals in the ZnO host matrix. The surface morphology modified from fibrous to spherical grain shape with enrichment of cobalt in the deposits. The composition analysis indicates the existence of Zinc and Cobalt. The XPS analysis provides the dopant exists in Co2+ state. The optical absorption edge shift to a higher wavelength of three band transitions corresponds to the 4A2→2 E(G), 4A2→4T1(P) and 4A2→2A1(G) states. The reduction of energy band gap Eg1 in the UV region and Eg2 in the visible region was observed, which is due to the spin exchange interaction occurs in the sp-d transition state. At room temperature photoluminescence (PL) spectra showed emission in the UV and entire visible region due to the various defect states present in the deposits. All deposits show paramagnetic behavior even at low temperature.

Persuasive Evidence for Electron-Nuclear Coupling in Diluted Magnetic Colloidal Nanoplatelets Using Optically Detected Magnetic Resonance Spectroscopy.

The incorporation of magnetic impurities into semiconductor nanocrystals with size confinement promotes enhanced spin exchange interaction between photogenerated carriers and the guest spins. This interaction stimulates new magneto-optical properties with significant advantages for emerging spin-based technologies. Here we observe and elaborate on carrier-guest interactions in magnetically doped colloidal nanoplatelets with the chemical formula CdSe/Cd1-xMnxS, explored by optically detected magnetic resonance and magneto-photoluminescence spectroscopy. The host matrix, with a quasi-type II electronic configuration, introduces a dominant interaction between a photogenerated electron and a magnetic dopant. Furthermore, the data convincingly presents the interaction between an electron and nuclear spins of the doped ions located at neighboring surroundings, with consequent influence on the carrier's spin relaxation time. The nuclear spin contribution by the magnetic dopants in colloidal nanoplatelets is considered here for the first time.

Triphenylene-Bridged Trinuclear Complexes of Cu: Models for Spin Interactions in Two-Dimensional Electrically Conductive Metal-Organic Frameworks.

Reaction of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaaminotriphenylene (HATP) with [Cu(Me3tacn)]2+ (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) produces trigonal tricopper complexes [(Me3tacnCu)3(HOTP)]3+ (1) and [(Me3tacnCu)3(HITP)]4+ (2) (HOTP, HITP = hexaoxy- and hexaiminotriphenylene, respectively). These trinuclear complexes are molecular models for spin exchange interactions in the two-dimensional conductive metal-organic frameworks (MOFs) copper hexaoxytriphenylene (Cu3HOTP2) and copper hexaiminotriphenylene (Cu3HITP2). Whereas complex 1 is isolated with HOTP3- bearing the same oxidation state as found in the oxy-bridged MOF, the triply oxidized HITP3- found in Cu3HITP2 is unstable with respect to disproportionation in the molecular model. Indeed, magnetic measurements reveal ligand-centered radical character for 1 and a closed-shell structure for 2, in agreement with the redox state of the ligands. All neighboring spins are antiferromagnetically coupled in 1 and 2. These results help probe metal-ligand-metal interactions in conductive MOFs and provide potential inspiration for the synthesis of other two-dimensional materials with delocalized electrons.

Pressure effect on hyperfine CPT resonance of ground-state Li atoms in glass hot-vapor cell

We report the hyperfine splitting frequency of ground-state lithium atoms. The frequency shift is induced by the collisions to helium and xenon buffer gases. Coherent population-trapping resonance between the hyperfine levels enables the frequency measurements in the range of pressure from 2 to $$54\,\hbox {kPa}$$ and temperature from 260 to $$400\,^{\circ }\hbox {C}$$ in borosilicate-glass cells. The buffer-gas density is self-consistently calibrated from the hyperfine splitting in the sealed cells. The resonance frequency and the line width provide an insight into collision-induced spin dynamics, where hyperfine-shift, spin-rotation, and spin-exchange interactions play an important role in atomic lithium vapor and buffer gas.

In-situ measurement of the density ratio of K-Rb hybrid vapor cell using spin-exchange collision mixing of the K and Rb light shifts.

We investigate a new method that enables the direct measurement of the density ratio of a K-Rb hybrid vapor cell, using the spin-exchange collision mixing of the K and Rb light shifts. The densities for each alkali metals can be further determined using Raoult's law. The mixture of the light shifts in both magnetometers and comagnetometers is formulated using Bloch equations and explained by considering the fast spin-exchange interaction. The relationship between the density ratio and the mixed light shifts is both formulated and simulated. The method was performed on several K-Rb magnetometer- and K-Rb-21Ne comagnetometer-cells at different temperatures, pump light powers, and mole fractions of K. The method was further verified by the conventional laser-absorption-spectroscopy method. The new approach has the advantage to measure the density ratio of the optically-thick hybrid alkali atoms, while requiring no additional magnetic field necessary for conventional magnetic-field induced Faraday-rotation techniques. It also has the advantage of in-situ measuring the density ratio under exactly the normal operation of the devices, which means that the errors caused by the heating-effect of the strong pump light and the temperature drift during long-term operation can be real-time monitored.

Interactions between nonresonant rf fields and atoms with strong spin-exchange collisions

We study the interactions between oscillating nonresonant rf fields and atoms with strong spin-exchange collisions in the presence of a weak dc magnetic field. We find that the atomic Larmor precession frequency shows a new functional form to the rf field parameters when the spin-exchange collision rate is tuned. In the weak rf field amplitude regime, a strong modification of atomic Larmor frequency appears when the spin-exchange rate is comparable to the rf field frequency. This effect has been neglected before due to its narrow observation window. We compare the experimental results with density matrix calculations, and explain the data by an underdamped oscillator model. When the rf field amplitude is large, there is a minimum atomic gyromagnetic ratio point due to the rf photon dressing, and we find that strong spin-exchange interactions modify the position of such a point.