Haina Wu

Exchange bias and its propagation in ferromagnetic/antiferromagnetic/ferromagnetic trilayers

We establish a simple ferromagnetic/antiferromagnetic/ferromagnetic trilayer model, where the lower-interface coupling is varied and study its combined effect with cooling field or temperature on the upper-interface exchange bias effect. Exchange bias field is almost independent of cooling field, if the lower-interface coupling is ferromagnetic and large. Otherwise, its value becomes sensitive to cooling field, and the evolution trend of exchange bias with increasing cooling field depends on the sign and strength of lower-interface coupling. On the other hand, the blocking temperature, below which exchange bias emerges, is reduced (or elevated) in the trilayers with a large ferromagnetic (or antiferromagnetic) lower-interface coupling. The numerical results obtained are interpreted well in terms of the magnetization behaviors in the respective layers. A cooling field creates a low-temperature frozen configuration in the antiferromagnetic layer after cooling to generate exchange bias, while such a configur...

Out-of-phase Andreev transports in a double-quantum-dot Cooper-pair splitter

We investigate the Andreev transports through a double-quantum-dot Cooper-pair splitter with an additional direct coupling between the dots. It is found that when finite magnetic flux is applied through this structure, its induced phase adjusts the local and crossed Andreev reflections in different manners. Moreover, in the presence of appropriate magnetic flux, the crossed Andreev reflection can be efficiently enhanced, accompanied by the suppression of the local Andreev reflection. Such a result exists in both the linear and nonlinear transport regions, even in the case of strong intradot Coulomb interaction. Therefore, such a work provides a promising scheme to enhance the splitting of the Cooper pair.

Thermoelectric and thermospin properties in a quantum ring with an embedded protein-like single-helical molecule

We investigate the thermoelectric and thermospin effects in a quantum ring whose arms are embedded by one protein-like single-helical molecule and one quantum dot, respectively. It shows that both the thermoelectric and thermospin effects are very distinct in this system. If one local magnetic flux is introduced through this ring, the thermospin effect can be efficiently enhanced, accompanied by the weakness of thermoelectric effect. Therefore, this work can be helpful for the achievement of the thermoelectric and thermospin effects, respectively.We investigate the thermoelectric and thermospin effects in a quantum ring whose arms are embedded by one protein-like single-helical molecule and one quantum dot, respectively. It shows that both the thermoelectric and thermospin effects are very distinct in this system. If one local magnetic flux is introduced through this ring, the thermospin effect can be efficiently enhanced, accompanied by the weakness of thermoelectric effect. Therefore, this work can be helpful for the achievement of the thermoelectric and thermospin effects, respectively.

Josephson effects in the junction formed by DIII-class topological and s-wave superconductors with an embedded quantum dot

We investigate the Josephson effects in the junction formed by the indirect coupling between DIII-class topological and s-wave superconductors via an embedded quantum dot. Due to the presence of two kinds of superconductors, three dot-superconductor coupling manners are considered, respectively. As a result, the Josephson current is found to oscillate in period 2π. More importantly, the presence of Majorana doublet in the DIII-class superconductor renders the current finite at the case of zero phase difference, with its sign determined by the fermion parity of such a junction. In addition, the dot-superconductor coupling plays a nontrivial role in adjusting the Josephson current. When the s-wave superconductor couples to the dot in the weak limit, the current direction will have an opportunity to reverse. It is believed that these results will be helpful for understanding the transport properties of the DIII-class superconductor.

Enhancement of the Cooper-pair splitting in the Fano interferometer

We investigate the Andreev transports through a single-dot Fano interferometer with a side-coupled superconductor. It is found that when a finite magnetic flux threads through this structure, its induced phase factor adjusts the local and crossed Andreev reflections in different manners. Moreover, the crossed Andreev reflection has the opportunity to be enhanced, accompanied by the suppression of the local Andreev reflection. Such a result also exists when the intradot Coulomb interaction is taken into account. Therefore, this structure can be a promising candidate for the enhancement of the Cooper-pair splitting.

Spin-polarized transport through a quantum ring with an embedded protein-like single-helical molecule

We investigate the spin-polarized electron transport through a quantum ring whose arms are embedded by one protein-like single-helical molecule and one quantum dot, respectively. It is found that the inter-arm quantum interference leads to the enhancement of the spin polarization in this structure. Moreover, when local magnetic flux is applied through the ring, the spin polarization in the electron transport process, including the polarization strength and direction, can be further adjusted. Next in the finite-bias case, the spin polarization is also apparent and can be tuned by changing the magnetic flux or the dot level. This work provides a new scheme to manipulate the spin transport based on the single-helical molecule.

Majorana modes in a triple-terminal Josephson junction with embedded parallel-coupled double quantum dots

Abstract We investigate the Josephson effect in one triple-terminal junction with embedded parallel-coupled double quantum dots. It is found that the inter-superconductor supercurrent has opportunities to oscillate in period 4 π , with the adjustment of the phase differences among the superconductors. What is notable is that such a result is robust and independent of fermion parities, intradot Coulomb strength, and the dot-superconductor coupling manner. By introducing the concept of spinful many-particle Majorana modes, we present the analytical definition of the Majorana operator via superposing electron and hole operators. It can be believed that this work provide a simple but feasible proposal for the realization of Majorana modes in a nonmagnetic system.

Josephson current through a quantum-dot ring: π-junction transition and persistent current magnification

By means of the exact diagonalization approach, the Josephson and persistent currents in a superconductor/quantum-dot ring/superconductor (S/QDR/S) structure are theoretically investigated. The ground state is obtained within zero bandwidth approximation in which the superconductors are replaced by effective local pairing potentials. It is found that Josephson current can flow through this structure in the presence of various electron correlations. Furthermore, in the half-filled case, a novel 0-π transition behavior is observed, which arises from the interplay of interdot antiferromagnetic coupling and electron correlations. When the symmetry of the two arms in the QDR is broken down, the quantum interference efficiently causes the persistent current magnification, even in the case of equilibrium and zero magnetic flux.