arXiv subjects

Yu Han

Publications and source records attributed to Yu Han.

151 records · Page 9Linked to original sources

arXiv2013

Action principle for the connection dynamics of scalar-tensor theories

A first-order action for scalar-tensor theories of gravity is proposed. The Hamiltonian analysis of the action gives the desired connection dynamical formalism, which was derived from the geometrical dynamics by canonical transformations. It is shown that this connection formalism in Jordan frame is equivalent to the alternative connection formalism in Einstein frame. Therefore, the action principle underlying loop quantum scalar-tensor theories is recovered.

gr-qc↗

arXiv2010

Detection of spin bias in four-terminal quantum-dot ring

In this work, we show that in a four-quantum-dot ring, via introducing a local Rashba spin-orbit interaction the spin bias in the transverse terminals can be detected by observing the charge currents in the longitudinal probes. It is found that due to the Rashba interaction, the quantum interference in this system becomes spin-dependent and the opposite-spin currents induced by the spin bias can present different magnitudes, so charge currents emerge. Besides, the charge currents rely on both the magnitude and spin polarization direction of the spin bias. It is believed that this method provides an electrical but practical scheme to detect the spin bias (or the spin current).

cond-mat.mes-hall↗

arXiv2009

Electronic transport through a double-quantum-dot Aharonov-Bohm interference device with impurities

The impurity-related electron transport through a double quantum dot (QD) Aharonov-Bohm (AB) interferometer is theoretically studied, by considering impurities coupled to the QDs in the interferometer arms. When investigating the linear conductance spectra \emph{vs} the impurity levels, we show that the impurities influence the electron transport in a nontrivial way, since their suppressing or enhancing the electron tunneling. A presented single-level impurity leads to the appearance of Fano lineshapes in the conductance spectra in the absence of magnetic flux, with the positions of Fano antiresonances determined by both the impurity-QD couplings and the QD levels separated from the Fermi level, whereas when a magnetic flux is introduced with the the phase factor $ϕ=π$ the impurity-driven Breit-Wigner lineshapes appear in the conductance curves. Besides, the nonlocal impurities alter the period of conductance change \emph{vs} the magnetic flux. The multi-level impurities indeed complicate the electron transport, but for the cases of two identical local impurities coupled to the respective QDs with uniform couplings or a nonlocal impurity coupled to both QDs uniformly, the antiresonances are only relevant to the impurity levels. When many-body effect is managed within the second-order approximation, we also find the important role of the Coulomb interaction in modifying the electron transport.

cond-mat.mes-hall↗

arXiv2009

Spin-bias driven electron properties of a triple-quantum-dot ring

Electron transport through a three-electrode triple-quantum-dot ring with the source electrode of spin-dependent splitting of chemical potentials (spin bias) is theoretically investigated. We find clear charge and spin currents in the drain electrodes driven by the spin bias, despite the absence of charge bias between the source and drain electrodes, and their directions and amplitudes can be adjusted by altering the structure parameters or magnetic field. The distinct characteristics of spin-bias driven persistent charge and spin currents in the ring are also shown. When an appropriate charge bias is applied, the single-spin electron motion can be achieved in this structure.

cond-mat.mes-hall↗

arXiv2009

Decoupling and antiresonance in electronic transport through a quantum dot chain embodied in an Aharonov-Bohm interferometer

Electronic transport through a quantum dot chain embodied in an Aharonov-Bohm interferometer is theoretically investigated. In such a system, it is found that only for the configurations with the same-numbered quantum dots side-coupled to the quantum dots in the arms of the interferometer, some molecular states of the quantum dot chain decouple from the leads. Namely, in the absence of magnetic flux all odd molecular states decouple from the leads, but all even molecular states decouple from the leads when an appropriate magnetic flux is introduced. Interestingly, the antiresonance position in the electron transport spectrum is independent of the change of the decoupled molecular states. In addition, when considering the many-body effect within the second-order approximation, we show that the emergence of decoupling gives rise to the apparent destruction of electron-hole symmetry. By adjusting the magnetic flux through either subring, some molecular states decouple from one lead but still couple to the other, and then some new antiresonances occur.

cond-mat.mes-hall↗

arXiv2009

Rashba-induced transverse pure spin currents in a four-terminal quantum dot ring

By applying a local Rashba spin-orbit interaction on an individual quantum dot of a four-terminal four-quantum-dot ring and introducing a finite bias between the longitudinal terminals, we theoretically investigate the charge and spin currents in the transverse terminals. It is found that when the quantum dot levels are separate from the chemical potentials of the transverse terminals, notable pure spin currents appear in the transverse terminals with the same amplitude and opposite polarization directions. Besides, the polarization directions of such pure spin currents can be inverted by altering structure parameters, i.e., the magnetic flux, the bias voltage, and the values of quantum dot levels with respect to the chemical potentials of the transverse terminals.

cond-mat.mes-hall↗

arXiv2008

Decoupling and antiresonance in a quantum dot chain with two neighboring dots coupled to both leads

Electron transport through a quantum dot chain with two neighboring dots coupled to both leads is theoretically studied. In such a system, it is found that only for the even-numbered quantum dot structure with the same-number quantum dots coupled to each connecting dot, some eigenstates of the quantum dots decouple from the leads. Namely, all odd eigenstates decouple from the leads in the absence of magnetic flux, but all even eigenstates will decouple from the leads when a magnetic flux is introduced. In addition, by adjusting the magnetic fluxes through any subring, some eigenstates decouple from one lead but still couple to the other, and then some new antiresonances occur.

cond-mat.mes-hall↗