En-Jia Ye

Magnetostructural transition and magnetocaloric effect in MnNiSi-Fe2Ge system

Magnetostructural transition from ferromagnetic orthorhombic phase to paramagnetic hexagonal phase can be obtained by chemically alloying appropriate amount of Fe2Ge into MnNiSi. The magnetostructural transition temperature is tunable in a wide temperature range of about 280 K. Saturation moment of the ferromagnetic orthorhombic phase increases from 2.62 μB/f.u. to 3.17 μB/f.u. with Fe2Ge-doping. The magnetostructural transition is accompanied by a large change of magnetization over 80 Am2/kg under magnetic field of 5 T. Relatively large magnetic entropy changes and working temperature ranges were observed in the vicinity of room temperature. Our findings suggest that MnNiSi-Fe2Ge material system is a promising platform for tunable magnetostructural transition and the associated magnetocaloric effect.

Thermal-cycling-dependent magnetostructural transitions in a Ge-free system Mn0.5Fe0.5Ni(Si,Al)

Magnetostructural transitions from low-temperature TiNiSi-type phases to high-temperature Ni2In-type phases had been observed in some MnCoGe-based and MnNiGe-based intermetallic systems. In this work, the TiNiSi-to-Ni2In-type magnetostructural transitions, which are associated with large changes in magnetization and large anisotropy lattice distortion, were obtained in a Ge-free system Mn0.5Fe0.5Ni(Si,Al) in the vicinity of room temperature. Thermal-cycling-dependent properties were observed in the as-prepared bulk polycrystalline samples. This phenomenon could be attributed to the presence of anisotropy internal stress and its release by spontaneously cracking across the thermally activated magnetostructural transitions.

Dynamic conductance in L-shaped graphene nanosystems

Dynamic conductance of nanocircuit, which demonstrates dc and ac transport properties, is regarded as vital indicator for device feature. With the help of nonequilibrium Greens function technology and Buttikers ac transport theory, we present dynamic conductance in L-shaped graphene nanosystems (LGNSs). It is found that electronic transport is highly sensitive to the geometric feature as well as the size of LGNSs. The armchair edge lead determines whether LGNS shows ac response or not around Dirac point. The increase of width of zigzag edge lead suppresses dc conductance and induces capacitive responses at the anti-resonance states. This is due to large dwell time originated from edge state in zigzag edge lead. In the energy region far away from Dirac point, LGNS responds inductively with the transportation channel opens. Behaviors of dynamic conductance at Dirac point and anti-resonance states are discussed by interesting spacial-resolved local density of states.

Linear ac transport in graphene semiconducting nanosystem with normal-metal electrodes

Linear ac transport properties are investigated in a graphene semiconducting nanosystem, with the effect of normal-metal electrodes taken into account. We use a tight-binding approach and ac transport theory to study the dc conductance and ac emittance in normal-metal/graphene (NG) and normal-metal/graphene/normal-metal (NGN) systems with armchair-edge graphene. We find that the resonant and semiconducting behaviors in NG and NGN systems are closely related to the spatial-resolved local density of states. Furthermore, features of the size-dependent emittances in the NGN system are investigated. The results suggest a positive correlation between the width and capacitive response, and the capacitive response is robust as the size of the system increases proportionally.

ELECTRON TRANSPORT IN MULTI-TERMINAL GRAPHENE NANODEVICE WITH INCLINED CROSS STRUCTURES

The DC and AC transport properties are investigated in multi-terminal graphene nanoribbon (GNR) devices. The devices are composed of three or four graphene ribbons connected with different angles. It is found that DC and AC conductances depend on the structural configurations and ribbon properties. In the vicinity of Dirac point, the intersection of graphene ribbons forms band mixing and results in resonant or anti-resonant states. The edge and width, as well as, the angles of the graphene ribbons influence the DC and AC transport properties drastically. These properties can be used to build future graphene-based nanoelectronics.

Thermal conductance attributed to phonon and electron in graphene nanoribbon

In this work, the energy transport of phonon and electron in graphene nanoribbons (GNRs) are investigated by the nonequilibrium Greens function method without considering the interaction of phonon and electron. The heat current of phonon contribution comes from the gradient of temperature. While for the electron contribution, it stems from the gradient of both temperature and electrochemical potential. The corresponding intermediate functions satisfy the Onsager relationship. Thermal conductances are calculated in GNR and compared to those in square lattice ribbon model respectively. It is found that both the phonon and electron thermal conductances in square lattice ribbon are smaller than those in GNRs at low temperature and surpass those in armchair and zigzag GNRs respectively, as the temperature increases. Meanwhile, the heat transport is related to the edges of GNRs. These phenomena depend on their dispersion relations and energy band structures.

Topologically Protected AC Transport Induced by Spin–Orbit Interaction in H-Shaped Silicene Nanojunction

The linear ac transport properties are theoretically studied in H-shaped zigzag silicene nanojunction. We numerically calculated the dc conductance and ac emittance by considering the nearest-neighbor hopping, the second-nearest-neighbor spin–orbit interaction (SOI), and external electric field, based on the tight-binding approach and the ac transport theory. It is found that the relatively large SOI induces a topological quantum edge state in the nanojunction, which eliminates the ac emittance response at the Dirac point. Further investigations indicate that the SOI-induced ac transport is topologically protected, despite the changes of geometric size. Moreover, the external electric field would open an energy gap, and destroy the topological quantum state, making the nanojunction a trivial band insulator.

Anions (N,S) mono-doping and co-doping influences on electronic structures and optical properties of InNbO4

In this paper, the electronic structures and optical properties of N-doped, S-doped and N/S-codoped InNbO4 were systematically investigated by first-principles calculations based on density functional theory (DFT). As for N-doped InNbO4, the acceptor N-2p states would introduce on the upper edge of the valence band (O-2p). While S-3p states would mix with O-2p states when O atom was replaced by S atom in InNbO4. As for N/S-codoped InNbO4, N-2p states mixed with S-3p states above the valence band, resulting in the energy bandgap further narrower in contrast to those of the individual N(S)-doped InNbO4. The optical absorption edge of N/S-codoped InNbO4 displayed an obvious redshift and was successfully extended to visible light region due to the synergistic effect of N/S co-doping. This research proposed that N/S co-doping was a promising method to improve the photocatalytic properties of InNbO4.

Charge Relaxation Resistances in Gated Graphene Nanoribbons

We investigate the charge relaxation resistances in a typical graphene nanoribbon FET (GNRFET). We show that the behavior of the charge relaxation resistances heavily depends on the exerted gate voltage and the structural details of the GNRFET. When there is 0 channel (blocked), 1 channel, and N channels in the GNR as tuned by the gate voltage, the equilibrium charge relaxation resistance is roughly 1, 1/2, and 1/2N of Sharvin-Imry contact resistance (h/2e2), respectively, whereas the nonequilibrium charge relaxation resistance is much smaller. Our results indicate that the charge relaxation resistances characterizing the information of dissipation, RC time and noise can be controlled by the gate voltage.