Spin Blockade Effect Research Articles

Pauli spin blockade in a resonant triple quantum dot molecule

A Pauli spin blockade in quantum dot systems occurs when the charge transport is allowed only for some spin states, and it has been an efficient tool in spin-based qubit devices in semiconductors. We theoretically investigate a Pauli spin blockade in a triple quantum dot molecule consisting of three identical quantum dots in a semiconductor in the presence of an external magnetic field through the molecule. When the three-electron state is on resonance with two- or four-electron states, the Aharonov–Bohm oscillation and the Zeeman splitting lead to a periodic spin blockade effect. We focus on the spin blockade at a two- and three-electron resonance and show that we can tune the magnetic field to selectively allow only either a spin-singlet or spin-triplet state to add an additional electron from tunnel-coupled leads. This spin blockade maintains the three quantum dots at the optimal sweet spot against the charge noise, demonstrating its potential as an efficient readout scheme for the qubits in quantum dot systems.

Strain dependent spin-blockade effect realization in the charge-disproportionated SrCoO2.5 thin films

The spin-blockade phenomena occur in the charge-ordered systems because of the non-conservation of the spin-states of the charges across the charge hopping process. Here, we have investigated the validation of the spin-blockade phenomena in a different kind of charge-ordered system, viz. charge-disproportionated SrCoO2.5 thin film, where O-2p hole is the key parameter for such charge-ordering. It is observed with the help of the polarization-dependent O K-edge x-ray absorption spectroscopy that the spin-blockade increases with the decrease in charge-disproportionation vis-à-vis O-2p hole density in the SrCoO2.5 films. The spin-blockade has been realized in terms of the lowest energy charge fluctuation energetics in the SrCoO2.5 films. Our results provide a fundamental understanding of the spin-blockade phenomena in both the usual charge-ordered and unusual charge-disproportionated systems, which would lead to a path forward toward novel material designing.

Chiral Molecules and the Spin Selectivity Effect.

This Perspective discusses recent experiments that bear on the chiral induced spin selectivity (CISS) mechanism and its manifestation in electronic and magnetic properties of chiral molecules and materials. Although the discussion emphasizes newer experiments, such as the magnetization dependence of chiral molecule interactions with ferromagnetic surfaces, early experiments, which reveal the nonlinear scaling of the spin filtering with applied potential, are described also. In many of the theoretical studies, one has had to invoke unusually large spin–orbit couplings in order to reproduce the large spin filtering observed in experiments. Experiments imply that exchange interactions and Pauli exclusion constraints are an important aspect of CISS. They also demonstrate the spin-dependent charge flow between a ferromagnetic substrate and chiral molecules. With these insights in mind, a simplified model is described in which the chiral molecule’s spin polarization is enhanced by a spin blockade effect to generate large spin filtering.

Network architecture of energy landscapes in mesoscopic quantum systems

Mesoscopic quantum systems exhibit complex many-body quantum phenomena, where interactions between spins and charges give rise to collective modes and topological states. Even simple, non-interacting theories display a rich landscape of energy states—distinct many-particle configurations connected by spin- and energy-dependent transition rates. The ways in which these energy states interact is difficult to characterize or predict, especially in regimes of frustration where many-body effects create a multiply degenerate landscape. Here, we use network science to characterize the complex interconnection patterns of these energy-state transitions. Using an experimentally verified computational model of electronic transport through quantum antidots, we construct networks where nodes represent accessible energy states and edges represent allowed transitions. We find that these networks exhibit Rentian scaling, which is characteristic of efficient transportation systems in computer circuitry, neural circuitry, and human mobility, and can be used to measure the interconnection complexity of a network. We find that the topological complexity of the state transition networks—as measured by Rent’s exponent— correlates with the amount of current flowing through the antidot system. Furthermore, networks corresponding to points of frustration (due, for example, to spin-blockade effects) exhibit an enhanced topological complexity relative to non-frustrated networks. Our results demonstrate that network characterizations of the abstract topological structure of energy landscapes capture salient properties of quantum transport. More broadly, our approach motivates future efforts to use network science to understand the dynamics and control of complex quantum systems.

Spin-entropy induced thermopower and spin-blockade effect in CoO

We report spin-entropy-induced thermopower and the occurrence of a spin-blockade effect in stoichiometric disordered CoO. Cation defect-driven distortion in the octahedral ligand field of CoO leads ...

Spin-Polarized Currents Induced by Multichannel Magnetic Point Contacts

We consider theoretically the spin blockade effect on the spin polarization of a current passing through a geometrically confined head-to-head 180∘ domain wall at a magnetic point contact in a two-dimensional (2D) metallic nanowire. The analysis is based on coherent scattering of the carriers by spin-dependent potential associated with the wall structure. The transmission properties of coherent states are obtained by introducing an algorithm to solve the coupled spin channels Schrödinger equation with mixed Dirichlet–Neumann boundary conditions applied far from the domain wall. It has been shown that a domain wall separating two media of opposite magnetization direction can act as a spin filter, allowing controllable modification of the spin polarization via the wall width.

Universal power law decay of spin polarization in double quantum dot

We study the spin dynamics and spin noise in a double quantum dot taking into account the interplay between hopping, exchange interaction and the hyperfine interaction. At short time scales the spin relaxation is governed by the spin dephasing in the random nuclear fields. At long time scales the spin polarization obeys universal power law $1/t$ independent of the relation between all the parameters of the system. This effect is related to the competition between the spin blockade effect and the hyperfine interaction. The spin noise spectrum of the system universally diverges as $\ln(1/\omega)$ at low frequencies.

Magnetoresistive properties of a double magnetic molecule spin valve in different geometrical arrangements

Abstract Spin-dependent transport through a spin valve consisting of two large-spin molecules, such as single molecular magnets, weakly coupled to external ferromagnetic electrodes is theoretically studied. The main focus is on the dependence of the tunneling current, its spin polarization, differential conductance and tunnel magnetoresistance on the arrangement of molecules embedded in the tunnel junction. These quantities are calculated by using the real-time diagrammatic technique in the lowest-order perturbation theory with respect to the coupling strength. When the molecules’ geometry is parallel, both an enhanced as well as inverse tunnel magnetoresistance can develop depending on the molecule’s occupation. On the other hand, if the two molecules form a serial geometry, a strong current-suppression occurs due to the Pauli spin blockade effect, resulting in negative differential conductance. In this transport regime we also find large tunnel magnetoresistance, which now exhibits strong asymmetry with respect to the bias voltage reversal. In addition, we show that an enhanced magnetoresistance and negative differential conductance can develop when a T-shaped molecular geometry is taken under consideration. These effects are explained by invoking particular occupation of molecular states and nonequilibrium spin accumulation that builds up in the case of the antiparallel magnetic configuration of the device.

High-temperature operation of a silicon qubit

This study alleviates the low operating temperature constraint of Si qubits. A qubit is a key element for quantum sensors, memories, and computers. Electron spin in Si is a promising qubit, as it allows both long coherence times and potential compatibility with current silicon technology. Si qubits have been implemented using gate-defined quantum dots or shallow impurities. However, operation of Si qubits has been restricted to milli-Kelvin temperatures, thus limiting the application of the quantum technology. In this study, we addressed a single deep impurity, having strong electron confinement of up to 0.3 eV, using single-electron tunnelling transport. We also achieved qubit operation at 5–10 K through a spin-blockade effect based on the tunnelling transport via two impurities. The deep impurity was implemented by tunnel field-effect transistors (TFETs) instead of conventional FETs. With further improvement in fabrication and controllability, this work presents the possibility of operating silicon spin qubits at elevated temperatures.

High temperature magnetic and transport properties of PrBaCo2O6–δ cobaltite: Spin blockade evidence

The experimental data are presented for magnetic susceptibility and electrical conductivity in PrBaCo2O6–δ at 850–1223 K. The decrease of oxygen content at heating is accompanied by formation of Co3+ cations that may simultaneously reside in oxygen pyramidal and octahedral coordination with intermediate and high spins, respectively. The small polaron p-type electron transport is shown to be mediated by the intermediate-spin Co3+ while high-spin Co3+ cations in octahedral environment are excluded from polaron jumps due to the spin blockade effect.

Inverse spin-valve effect in nanoscale Si-based spin-valve devices

We investigated the spin-valve effect in nano-scale silicon (Si)-based spin-valve devices using a Fe/MgO/Ge spin injector/detector deposited on Si by molecular beam epitaxy. For a device with a 20 nm Si channel, we observed clear magnetoresistance up to 3% at low temperature when a magnetic field was applied in the film plane along the Si channel transport direction. A large spin-dependent output voltage of 20 mV was observed at a bias voltage of 0.9 V at 15 K, which is among the highest values in lateral spin-valve devices reported so far. Furthermore, we observed that the sign of the spin-valve effect is reversed at low temperatures, suggesting the possibility of a spin-blockade effect of defect states in the MgO/Ge tunneling barrier.

Magnetic-anisotropy-induced spin blockade in a single-molecule transistor

We present a mechanism for a spin blockade effect associated with a change in the type of magnetic anisotropy over oxidation state in a single molecule transistor, by taking an example of an individual ${\mathrm{Eu}}_{2}{({\mathrm{C}}_{8}{\mathrm{H}}_{8})}_{3}$ molecule weakly coupled to nonmagnetic electrodes without linker groups. The molecule switches its magnetization direction from in-plane to out-of-plane when it is charged. In other words, the magnetic anisotropy of the molecule changes from easy plane to easy axis when the molecule is charged. By solving the master equation based on a model Hamiltonian, we find that current through the molecule is highly suppressed at low bias independently of gate voltage due to the interplay between spin selection rules and the change in the type of magnetic anisotropy. Transitions between the lowest magnetic levels in successive charge states are forbidden because the magnetic levels differ by $|\mathrm{\ensuremath{\Delta}}M|>1/2$ due to the change in the type of magnetic anisotropy, although the total spins differ by $|\mathrm{\ensuremath{\Delta}}S|=1/2$. This current suppression can be lifted by significant $\mathbf{B}$ field, and the threshold $\mathbf{B}$ field varies as a function of the field direction and the strength of magnetic anisotropy. The spin blockade effect sheds light on switching the magnetization direction by non-spin-polarized current and on exploring effects of this property coupled to other molecular degrees of freedom.

Coherent manipulation of a single magnetic atom using polarized single electron transport in a double quantum dot

We consider theoretically a magnetic impurity spin driven by polarized electrons tunneling through a double quantum dot system. Spin blockade effect and spin conservation in the system make the magnetic impurity sufficiently interact with each transferring electron. As a results, a single collected electron carries information about spin change of the magnetic impurity. The scheme may develop all electrical manipulation of magnetic atoms by means of single electrons, which is significant for the implementation of scalable logical gates in information processing systems.

Influence of electron—phonon interaction on the properties of transport through double quantum dot with ferromagnetic leads

Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC microwave driving field. The corresponding currents and differential conductance are calculated in the Coulomb blockade regime by means of the Born—Markov master equation. It is shown that the interplay between electrons and phonons gives rise to phonon-assisted tunneling resonances and Franck—Condon blockade under certain conditions. In noncollinear magnetic configurations, spin-blockade effects are also observed, and the angle of polarization has some influence on the transport characteristics.

Theory of electronic properties and quantum spin blockade in a gated linear triple quantum dot with one electron spin each

We present a theory of electronic properties and the spin blockade phenomena in a gated linear triple quantum dot. Quadruple points where four different charge configurations are on resonance, particularly involving (1,1,1) configuration, are considered. In the symmetric case, the central dot is biased to higher energy and a single electron tunnels through the device when (1,1,1) configuration is resonant with (1,0,1),(2,0,1),(1,0,2) configurations. The electronic properties of a triple quantum dot are described by a Hubbard model containing two orbitals in the two unbiased dots and a single orbital in the biased dot. The transport through the triple quantum dot molecule involves both singly and doubly occupied configurations and necessitates the description of the (1,1,1) configuration beyond the Heisenberg model. Exact eigenstates of the triple quantum dot molecule with up to three electrons are used to compute current assuming weak coupling to the leads and non-equilibrium occupation of quantum molecule states obtained from the rate equation. The intra-molecular relaxation processes due to acoustic phonons and cotunneling with the leads are included, and are shown to play a crucial role in the spin blockade effect. We find a quantum interference-based spin blockade phenomenon at low source-drain bias and a distinct spin blockade due to a trap state at higher bias. We also show that, for an asymmetric quadruple point with (0,1,1),(1,1,1,),(0,2,1),(0,1,2) configurations on resonance, the spin blockade is analogous to the spin blockade in a double quantum dot.

Mesoscopic admittance of a double quantum dot

We calculate the mesoscopic admittance $G(\omega)$ of a double quantum dot (DQD),which can be measured directly using microwave techniques. This quantity reveals spectroscopic information on the DQD and is also directly sensitive to a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a high quality photonic resonator. When the photon correlation functions can be developed along a random-phase-approximation-like scheme, the response of the resonator gives an access to $G(\omega)$.

Controlling and Detecting Spin Correlations of Ultracold Atoms in Optical Lattices

We report on the controlled creation of a valence bond state of delocalized effective-spin singlet and triplet dimers by means of a bichromatic optical superlattice. We demonstrate a coherent coupling between the singlet and triplet states and show how the superlattice can be employed to measure the singlet-fraction employing a spin-blockade effect. Our method provides a reliable way to detect and control nearest-neighbor spin correlations in many-body systems of ultracold atoms. Being able to measure these correlations is an important ingredient in studying quantum magnetism in optical lattices. We furthermore employ a SWAP operation between atoms which are part of different triplets, thus effectively increasing their bond-length. Such a SWAP operation provides an important step towards the massively parallel creation of a multiparticle entangled state in the lattice.

DNA-backbone radio resistivity induced by spin blockade effect

Coherent control of OH-free radicals interacting with the spin-triplet state of a DNA molecule is investigated. A model Hamiltonian for molecular spin singlet-triplet resonance is developed. We illustrate that the spin-triplet state in DNA molecules can be efficiently populated, as the spin-injection rate can be tuned to be orders of magnitudes greater than the decay rate due to small spin-orbit coupling in organic molecules. Owing to the nano-second life-time of OH free radicals, a non-equilibrium free energy barrier induced by the injected spin triplet state that lasts approximately longer than one-micro second in room temperature can efficiently block the initial Hydrogen abstraction and DNA damage. For a direct demonstration of the spin-blockade effect, a molecular simulation based on an ab-initio Car-Parrinello molecular dynamics is deployed.

Thermoelectric Response Driven by Spin-State Transition in La1−xCexCoO3 Perovskites

An unusual thermoelectric response was observed in n-type perovskite oxide La1−xCexCoO3. Combining transport and magnetic measurements, we found that the thermoelectric response is driven by the spin-state transition of Co3+. This transition destroys the spin blockade effect and induces an abrupt decrease of resistivity as well as an insulator−metal transition. In contrast to the resistivity change, changes in thermopower and thermal conductivity are moderate. Consequently, a peak of figure of the merit ZT is present in a narrow temperature range. The room-temperature ZT ≈ 0.018 of La0.94Ce0.06CoO3 is comparable to that of p-type NaxCoO2. These observations can be helpful for the search and design of new thermoelectric materials.

Spin blockade and nuclear spin effect in a g-factor modulated vertical double quantum dot

We report on-going research on a low temperature transport properties of a g-factor modulated vertical double quantum dot device. The double dot consists of GaAs dot and In 0.04 Ga 0.96 As dot, and electron g-factors of two dots are largely different from each other. We observed a step like change of a leakage current in spin-blockade region as a function of magnetic field or source–drain voltage, and found that the position of current step in magnetic field decreases with increasing the source–drain voltage. We attribute the current step comes from nuclear-spin-assisted electron spin scatterings. At this magnetic field the two-electron spin singlet and triplet state energy crossover. Our model consisting of two-electron and two-site Hubbard Hamiltonian with different g-factor on each site gives good agreement between the observed magnetic field and source–drain voltage relation and the calculated one.