arXiv subjects

M. N. Chen

Publications and source records attributed to M. N. Chen.

10 recordsLinked to original sources

arXiv2023

Plasmonic detection of the parity anomaly in a two-dimensional Chern insulator

In this work, we present an analytical study on the surface plasmon polaritons in a two dimensional parity anomaly Chern insulator. The connections between the topology in the bulk implied by the BHZ model and the dispersion relations of the surface plasmons have been revealed. Anisotropy has been considered during the calculations of the dispersion relations which allows different permittivities perpendicular to the conductive plane. Two surface plasmon modes each contains two branches of dispersion relations have been found. The topologically non-trivial case gives quite different Hall conductivities compared with the trivial one, which leads to significant modifications of the dispersion curves or even the absence of particular branch of the surface plasmons. Our investigations pave a possible way for the detection of the parity anomaly in a two-dimensional Chern insulator via plasmonic responses.

cond-mat.mes-hall↗

arXiv2022

Disorder-induced phase transitions in double Weyl semimetals

The double Weyl semimetal (DWSM) is a newly proposed topological material that hosts Weyl points with chiral charge n=2. The disorder effect in DWSM is investigated by adopting the tight-binding Hamiltonian. Using the transfer matrix method and the noncommutative Kubo formula, we numerically calculate the localization length and the Hall conductivity in the presence of the on-site nonmagnetic disorder or orbital (spin-flip) disorders, and give the corresponding global phase diagrams. For the on-site nonmagnetic disorder, the system undergoes the DWSM-3D quantum anomalous hall (3D QAH) and normal insulator (NI)-DWSM phase transitions, and evolves into the diffusive metal (DM) phase before being localized by strong disorders, which is consistent with the Weyl semimetal. For σ_x orbital disorder, we find that increasing disorder can generate a pair of Weyl nodes at the boundary of the Brillouin zone and induce a 3D QAH-DWSM phase transition. Then we investigate the combined effect of orbital disorders for both disordered 3D QAH phase and DWSM phase. The disorder-induced transitions can be well understood in terms of an effective medium theory based on self-consistent Born approximation.

cond-mat.mes-hall↗

arXiv2021

Giant anisotropic photocurrent modulated by strain in type-II Weyl semimetal Td-MoTe2

We build a Cu-MoTe2-Cu device model and use first-principles density functional theory to study the transport properties of single-layer Td-MoTe2. We obtained the effect of strain on the energy band structure, transport properties, and photocurrent. The strain-induced photocurrent shows an anisotropy that reflects the modulation of the energy bands, including the Weyl point, by strain. The photocurrent can be suppressed to almost zero when the strain is applied along the vacuum direction. In contrast, the photocurrent can be significantly increased when the strain is applied along the transport direction. The transport properties and magnitude of the photocurrent in the MoTe2-based device can be effectively modulated by adjusting the strength and direction of the strain.

cond-mat.mtrl-sci↗

arXiv2021

Valley-dependent transport in strain engineering graphene heterojunctions

We study the effect of the strain on the band structure and the valley-dependent transport property of graphene heterojunctions. It is found that valley-dependent separation of electrons can be achieved by utilizing the strain and on-site energies. In the presence of the strain, the values of the transmission can be effectively adjusted by changing the strengths of the strain, while the transport angle basically keeps unchanged. When an extra on-site energy is simultaneously applied to the central scattering region, not only are the electrons of valleys K and K' separated into two distinct transmission lobes in opposite transverse directions, but the transport angles of two valleys can be significantly changed. Therefore, one can realize an effective modulation of valley-dependent transport by changing the strength and stretch angle of the strain and on-site energies, which can be exploited for graphene-based valleytronics devices.

cond-mat.mes-hall↗

arXiv2021

Topological hybrid semimetal phases and anomalous Hall effects in a three dimensional magnetic topological insulator

In this work, we propose a ferromagnetic Bi$_2$Se$_3$ as a candidate to hold the coexistence of Weyl- and nodal-line semimetal phases, which breaks the time reversal symmetry. We demonstrate that the type-I Weyl semimetal phase, type-I-, type-II- and their hybrid nodal-line semimetal phases can arise by tuning the Zeeman exchange field strength and the Fermi velocity. Their topological responses under U(1) gauge field are also discussed. Our results raise a new way for realizing Weyl and nodal-line semimetals and will be helpful in understanding the topological transport phenomena in three-dimensional material systems.

cond-mat.mes-hall↗

arXiv2021

Scaling of the Reduced Energy Spectrum of Random Matrix Ensemble

We study the reduced energy spectrum $\{E_{i}^{(n)}\}$, which is constructed by picking one level from every $n$ levels of the original spectrum $\{E_{i}\}$, in a Gaussian ensemble of random matrix with Dyson index $β\in \left( 0,\infty \right) $. It's shown $\{E_{i}^{(n)}\}$ bears the same form of probability distribution as $\{E_{i}\}$ with a rescaled parameter $γ=\frac{n(n+1)}{2}β+n-1$. Notably, the $n$-th order level spacing and non-overlapping gap ratio in $\{E_{i}\}$ become the lowest-order ones in $\{E_{i}^{(n)}\}$, hence their distributions will rescale in an identical way. Numerical evidences are provided by simulating random spin chain as well as modelling random matrices. Our results establish the higher-order spacing distributions in random matrix ensembles beyond GOE,GUE,GSE, and reveals a hierarchy of structures hidden in the energy spectrum.

cond-mat.dis-nn↗

arXiv2016

Effect of the edge states on the conductance and thermopower in Zigzag Phosphorene Nanoribbons

We numerically study the effect of the edge states on the conductance and thermopower in zigzag phosphorene nanoribbons (ZPNRs) based on the tight-binding model and the scattering-matrix method. It is interesting to find that the band dispersion, conductance, and thermopower can be modulated by applying a bias voltage and boundary potentials to the two layers of the ZPNRs. Under the certain bias voltage, the two-fold degenerate quasi-flat edge bands split perfectly. The conductance can be switched off, and the thermopower around zero energy increases. In addition, when only the boundary potential of the top layer or bottom layer is adjusted, only one edge band bends and merges into the bulk band. The first conductance plateau is strongly decreased to $e^2/h$ around zero energy. Particularly, when the two boundary potentials are adjusted, all the edge bands bend and fully merge into the bulk band, and the bulk energy gap is maximized. More interestingly, a pronounced conductance plateau with $G=0$ is found around zero energy, which is attributable to the opening of the bulk energy gap between the valence and conduction bands. Meanwhile, the thermopower can be enhanced more than twice, compared to that of the perfect ZPNRs. The large magnitude of thermopower is ascribed to the appearance of the bulk energy gap around zero energy. Our results show that the modulated ZPNRs are more reliable in thermoelectric application.

cond-mat.mes-hall↗

arXiv2016

Electron Interaction Effects in Periodically Driven Kitaev Model: Topology Breaking and Enhancement of Quantum Chaos

The effect of electron-electron interaction on Floquet topological superconducting chains is investigated numerically through full diagonalization and time evolution. The preservation of topology in the weak interacting regime is represented by a many-body form of the Majorana survival probability, and the emergence of chaos is characterized using the level statistics. In the presence of weak interaction, there appear a multitude of avoided crossings in quasi-energy spectra, and the resulting chaos is not full but can coexist with the topology. Strong interaction will lead the system into a topologically trivial and fully chaotic phase.

cond-mat.str-el↗

arXiv2016

Non-adiabatic topological spin pumping

Based on the Floquet scattering theory, we analytically investigate the topological spin pumping for an exactly solvable model. Floquet spin Chern numbers are introduced to characterize the periodically time-dependent system. The topological spin pumping remains robust both in the presence and in the absence of the time-reversal symmetry, as long as the pumping frequency is smaller than the band gap, where the electron transport involves only the Floquet evanescent modes in the pump. For the pumping frequency greater than the band gap, where the propagating modes in the pump participate in the electron transport, the spin pumping rate decays rapidly, marking the end of the topological pumping regime.

cond-mat.mes-hall↗

arXiv2016

Spin Chern Pumping from the Bulk of Two-Dimensional Topological Insulators

Topological insulators (TIs) are a new quantum state of matter discovered recently, which are characterized by unconventional bulk topological invariants. Proposals for practical applications of the TIs are mostly based upon their metallic surface or edge states. Here, we report the theoretical discovery of a bulk quantum pumping effect in a two-dimensional TI electrically modulated in adiabatic cycles. In each cycle, an amount of spin proportional to the sample width can be pumped into a nonmagnetic electrode, which is attributed to nonzero spin Chern numbers $C_{\pm}$. Moreover, by using a half-metallic electrode, universal quantized charge pumping conductivities $-C_{\pm}e^2/h$ can be measured. This discovery paves the way for direct investigation of the robust topological properties of the TIs.

cond-mat.mes-hall↗