arXiv subjects

Mou Yang

Publications and source records attributed to Mou Yang.

17 recordsLinked to original sources

arXiv2026

RKKY interaction as a probe of valley-dependent spin splitting and odd-parity nature in Floquet collinear magnets

Odd-parity magnets were recently proposed to emerge in collinear antiferromagnets (AFMs) via Floquet engineering, with valley-dependent spin splitting underlying the odd-parity spin polarization. This proposal brings about two key challenges: detecting the spin splitting to verify the generation mechanism of these magnets, and identifying such polarization to confirm the odd-parity nature. Here, we show that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction provides a unified magnetic probe for both tasks. Taking collinear $f$-wave magnets as a representative example, we find that the RKKY interaction yields distinct magnetic signals of the spin splitting---including a magnetism reversal in the Heisenberg/Ising terms and a sign alternation of the Dzyaloshinskii-Moriya (DM) term---that enable clear discrimination of collinear $f$-wave magnets from other related AFMs. Moreover, the DM term exhibits an $f$-wave shape with odd-parity symmetry, satisfying $J^{\alpha\beta}_{DM}(\mathbf{R}) = -J^{\alpha\beta}_{DM}(C_{2q}\mathbf{R})$ ($q=3$), which directly reflects the odd-parity spin polarization $S_z(\mathbf{k}) = -S_z(C_{2q}\mathbf{k})$ in momentum space. This behavior persists in $p$-wave magnets ($q=1$), demonstrating the generality of our approach. Our work establishes the RKKY interaction as a versatile probe for detecting band features of collinear odd-parity magnets, with predictions accessible to existing experimental techniques such as spin-polarized scanning tunneling spectroscopy.

cond-mat.mes-hall↗

arXiv2025

Anisotropy-induced collapse of Landau levels in Weyl semimetals and its detection via the planar Hall effect

The planar Hall effect (PHE) is a powerful tool for characterizing Weyl semimetals (WSMs). Here, we inves- tigate the PHE in general anisotropic WSMs under strong magnetic fields. We analytically derive the Landau levels (LLs) and their wavefunctions using the Bogoliubov transformation, where the tilt vector, anisotropic axis of the Fermi velocity, and the magnetic field can be oriented in arbitrary directions. Notably, due to the interaction with the magnetic field and the anisotropy of the Fermi velocity, the component of the tilt vector perpendicular to the magnetic field can induce a tilt in the LLs parallel to the magnetic field. Our analytical re- sults show that the LLs do not collapse in type-I WSMs but must collapse in type-II WSMs when the magnetic field is vertical to the tilt vector. More importantly, we demonstrate that the magnetotransport signal of the LL collapse, which manifests as significant enhancement and quantum oscillations in the longitudinal and planar Hall conductivities simultaneously, can be used to identify the phase transition from type-I to type-II WSMs.

cond-mat.mes-hall↗

arXiv2024

Modulation of chiral anomaly and bilinear magnetoconductivity in Weyl semimetals by impurity-resonance states

The phenomenon of nonlinear transport has attracted tremendous interest within the condensed matter community. We present a theoretical framework for nonlinear transport based on the nonequilibrium retarded Green's function, and examine the impact of disorder on nonlinear magnetotransport in Weyl semimetals (WSMs). It is demonstrated that bilinear magnetoconductivity can be induced in disordered WSMs by several mechanisms, including impurity-induced tilting of the Weyl cones, Lorentz-force-induced normal orbital magnetic moment, and chiral anomaly arising from the Berry-curvature-induced anomalous orbital magnetic moment. Additionally, we observe that the localization of Weyl fermions by impurity scattering will lead to resonant dips in both the chiral chemical potential and magnetoconductivity when the Fermi energy approaches the impurity resonance states. Our findings offer a theoretical proposition for modulating nonreciprocal transport in topological semimetals.

cond-mat.str-el↗

arXiv2024

RKKY signals characterizing the topological phase transitions in Floquet Dirac semimetals

Recently, the Floquet ${\rm Na_3Bi}$-type material has been proposed as an ideal platform for realizing various phases, i.e., the spin-degenerate Dirac semimetal (DSM) can be turned into the Weyl semimetal (WSM), and even to the Weyl half-metal (WHM). Instead of the conventional electrical methods, we use the RKKY interaction to characterize the topological phase transitions in this paper. It is found that detecting the Ising term $J_I$ is feasible for distinguishing the phase transition of DSM/WSM, since the emergence of $J_I$ is induced by the broken spin degeneracy. For the case with impurities deposited on $z$ axis (the line connecting the Weyl points), the Heisenberg term $J_H$ coexists with $J_I$ in the WSM, while $J_H$ is filtered out and only $J_I$ survives in the WHM. This magnetic filtering effect is a reflection of the fully spin-polarized property (one spin band is in the WSM phase while the other is gapped) of the WHM, and it can act a signal to capture the phase transition of WSM/WHM. This signal can not be disturbed unless the direction of the impurities greatly deviates from $z$ axis. Interestingly, as the impurities are moved into the $x$-$y$ plane, there arises another signal (a dip structure for $J_H$ at the phase boundary), which can also identify the phase transition of WSM/WHM. Furthermore, we have verified that all magnetic signals are robust to the term that breaks the electron-hole symmetry. Besides characterizing the phase transitions, our results also suggest that the Floquet DSMs are power platforms for controlling the magnetic interaction.

cond-mat.mes-hall↗

arXiv2022

Indirect magnetic signals mediated by a single surface band in Weyl semimetals

Recently, abundant transport phenomena characterizing the surface states of Weyl semimetals (WSMs) have been reported. To generate these phenomena, electrons have to complete a closed intersurface orbit. Due to the unavoidable impurities in real materials, this orbit would be destroyed by the impurity scattering, which limits the detection of the surface states in WSMs. Here, we investigate the RKKY interaction between magnetic impurities, solely mediated by a single surface band, in semi-infinite WSMs. It is found that peculiar oscillations and slowly decaying laws of the RKKY interaction can act as the signals to capture the dispersive nature of the surface states of WSMs. The underlying physics is attributed to two effects: the band-edge effect and the bending effect of the surface band, which can control the RKKY interaction individually or compete with each other to produce more complex magnetic behaviors. In addition, the band-edge effect together with the finite Fermi energy would result in another interesting oscillation with battering pattern. All the results are significantly different from that in previous literatures where surface states have to couple with bulk states (or other surface states of different spins) to generate nonzero magnetic interaction. Compared to the previous models of surface states, the model here is more practical and is helpful for the deeper understanding of the surface magnetic properties in WSMs.

cond-mat.mes-hall↗

arXiv2020

The prolonged decay of RKKY interactions by interplay of relativistic and non-relativistic electrons in semi-Dirac semimetals

The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction has been extensively explored in isotropic Dirac systems with linear dispersion, which typically follows an exponent decaying rate with the impurity distance $R$, i.e., $J\propto 1/R^d$ ($1/R^{2d-1}$) in $d$-dimensional systems at finite (zero) Fermi energy. This fast decay makes it rather difficult to be detected and limits its application in spintronics. Here, we theoretically investigate the influence of anisotropic dispersion on the RKKY interaction, and find that the introduction of non-relativistic dispersion in semi-Dirac semimetals (S-DSMs) can significantly prolong the decay of the RKKY interaction and can remarkably enhance the Dzyaloshinskii-Moriya interaction around the relativistic direction. The underlying physics is attributed to the highly increased density of states in the linear-momentum direction as a result of the interplay of relativistic and non-relativistic electrons. Furthermore, we propose a general formula to determine the decaying rate of the RKKY interaction, extending the typical formula for isotropic DSMs. Our results suggest that the S-DSM materials are a powerful platform to detect and control the magnetic exchange interaction, superior to extensively adopted isotropic Dirac systems.

cond-mat.mes-hall↗

arXiv2017

Transport theory for electrical detection of the spin texture and spin-momentum locking of topological surface states

The surface states of three-dimensional topological insulators exhibit a helical spin texture with spin locked to momentum. To date, however, the direct all-electrical detection of the helical spin texture has remained elusive owing to the lack of necessary spin-sensitive measurements. We here provide a general theory for spin polarized transports of helical Dirac electrons through spin-polarized scanning tunneling microscopy (STM). It is found that different from conventional magnetic materials, the tunneling conductance through the TI surface acquires an extra component determined by the in-plane spin texture, exclusively associated with spin momentum locking. Importantly, this extra conductance unconventionally depends on the spatial azimuthal angle of the magnetized STM tip, which is never carried out in previous STM theory. By magnetically doping to break the symmetry of rotation and time reversal of the TI surface, we find that the measurement of the spatial resolved conductance can reconstruct the helical structure of spin texture. Furthermore, one can extract the SML angle if the in-plane magnetization is induced purely by the spin-orbit coupling of surface Dirac elections. Our theory offers an alternative way, rather than using angle resolved photoemission spectroscopy, to electrical identify the helical spin texture on TI surfaces.

cond-mat.mes-hall↗

arXiv2017

Signature of topological phase transition in the RKKY interaction of silicene

Silicene offers an ideal platform for exploring the phase transition due to strong spin-orbit interaction and its unique structure with strong tunability. With applied electric field and circularly polarized light, siliccene is predicted to exhibit rich phases. We propose that these intricate phase transitions can be detected by measuring the bulk Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. We have in detail analyzed the dependence of RKKY interaction on phase parameters for different impurity configurations along zigzag direction. Importantly, we present an interesting comparison between different terms of RKKY interaction with phase diagram. It is found that the in-plane and out-of-plane terms can exhibit the local extreme value or change of sign at the phase critical point and remarkable difference in magnitude for different phase regions. Consequently, the magnetic measurement provides unambiguous signatures to identify various types of phase transition simultaneously, which can be carried out with present technique.

cond-mat.mes-hall↗

arXiv2016

Electronic structure and optic absorption of phosphorene under strain

We studied the electronic structure and optic absorption of phosphorene (monolayer of black phosphorus) under strain. Strain was found to be a powerful tool for the band structure engineering. The in-plane strain in armchair or zigzag direction changes the effective masse components along both directions, while the vertical strain only has significant effect on the effective mass in the armchair direction. The band gap is narrowed by compressive in-plane strain and tensile vertical strain. Under certain strain configurations, the gap is closed and the energy band evolutes to the semi-Dirac type: the dispersion is linear in the armchair direction and is gapless quadratic in the zigzag direction. The band-edge optic absorption is completely polarized along the armchair direction, and the polarization rate is reduced when the photon energy increases. Strain not only changes the absorption edge, but also the absorption polarization.

cond-mat.mes-hall↗

arXiv2016

Spin helical states and spin transport of the line defect in silicene lattice

We investigated the electronic structure of a silicene-like lattice with a line defect under the consideration of spin-orbit coupling. In the bulk energy gap, there are defect related bands corresponding to spin helical states localized beside the defect line: spin-up electrons flow forward on one side near to the line defect and move backward on the other side, and vice verse for spin-down electrons. When the system is subjected to random distribution of spin-flipping scatterers, electrons suffer much less spin-flipped scattering when they transport along the line defect than in the bulk. An electric gate above the line defect can tune the spin-flipped transmission, which makes the line defect as a spin-controllable waveguide.

cond-mat.mes-hall↗

arXiv2016

Valley detection using a graphene gradual pn junction with spin-orbit coupling: an analytical conductance calculation

Graphene pn junction is the brick to build up variety of graphene nano-structures. The analytical formula of the conductance of graphene gradual pn junctions in the whole bipolar region has been absent up to now. In this paper, we analytically calculated that pn conductance with the spin-orbit coupling and stagger potential taken into account. Our analytical expression indicates that the energy gap causes the conductance to drop a constant value with respect to that without gap in a certain parameter region, and manifests that the curve of the conductance versus the stagger potential consists of two Gaussian peaks -- one valley contributes one peak. The latter feature allows one to detect the valley polarization without using double-interface resonant devices.

cond-mat.mes-hall↗

arXiv2016

Topologically trivial and nontrivial edge bands in graphene induced by irradiation

We proposed a minimal model to describe the Floquet band structure of two-dimensional materials with light-induced resonant inter-band transition. We applied it to graphene to study the band features caused by the light irradiation. Linearly polarized light induces pseudo gaps (gaps are functions of wavevector), and circularly polarized light causes real gaps on the quasi-energy spectrum. If the polarization of light is linear and along the longitudinal direction of zigzag ribbons, flat edge bands appear in the pseudo gaps, and if is in the lateral direction of armchair ribbons, curved edge bands can be found. For the circularly polarized cases, edge bands arise and intersect in the gaps of both types of ribbons. The edge bands induced by the circularly polarized light are helical and those by linearly polarized light are topologically trivial ones. The Chern number of the Floquet band, which reflects the number of pairs of helical edge bands in graphene ribbons, can be reduced into the winding number at resonance.

cond-mat.mes-hall↗

arXiv2015

General monogamy relation of multi-qubit systems in terms of squared R\'{e}nyi-$\alpha$ entanglement

We prove that the squared R\'{e}nyi-$\alpha$ entanglement (SR$\alpha$E), which is the generalization of entanglement of formation (EOF), obeys a general monogamy inequality in an arbitrary $N$-qubit mixed state. Furthermore, for a class of R\'{e}nyi-$\alpha$ entanglement, we prove that the monogamy relations of the SR$\alpha$E have a hierarchical structure when the $N$-qubit system is divided into $k$ parties. As a byproduct, the analytical relation between the R\'{e}nyi-$\alpha$ entanglement and the squared concurrence is derived for bipartite $2\otimes d$ systems. Based on the monogamy properties of SR$\alpha$E, we can construct the corresponding multipartite entanglement indicators which still work well even when the indicators based on the squared concurrence and EOF lose their efficacy. In addition, the monogamy property of the $\mu$-th power of R\'{e}nyi-$\alpha$ entanglement is analyzed.

quant-ph↗

arXiv2015

Entanglement and measurement-induced nonlocality of mixed maximally entangled states in multipartite dynamics

The maximally entangled state can be in a mixed state as well as the well-known pure state. Taking the negativity as a measure of entanglement, we study the entanglement dynamics of bipartite, mixed maximally entangled states (MMESs) in multipartite cavity-reservoir systems. It is found that the MMES can exhibit the phenomenon of entanglement sudden death, which is quite different from the asymptotic decay of the pure-Bell-state case. We also find that maximal entanglement cannot guarantee maximal nonlocality and the MMES does not correspond to the state with maximal measurement-induced nonlocality (MIN). In fact, the value and dynamic behavior of the MIN for the MMESs are dependent on the mixed state probability. In addition, we investigate the distributions of negativity and the MIN in a multipartite system, where the two types of correlations have different monogamous properties.

quant-ph↗

arXiv2014

Valley-dependent gauge fields for ultracold atoms in square optical superlattices

We propose an experimental scheme to realize the valley-dependent gauge fields for ultracold fermionic atoms trapped in a state-dependent square optical lattice. Our scheme relies on two sets of Raman laser beams to engineer the hopping between adjacent sites populated by two-component fermionic atoms. One set of Raman beams are used to realize a staggered π-flux lattice, where low energy atoms near two inequivalent Dirac points should be described by the Dirac equation for spin-1/2 particles. Another set of laser beams with proper Rabi frequencies are added to further modulate the atomic hopping parameters. The hopping modulation will give rise to effective gauge potentials with opposite signs near the two valleys, mimicking the interesting strain-induced pseudo-gauge fields in graphene. The proposed valley-dependent gauge fields are tunable and provide a new route to realize quantum valley Hall effects and atomic valleytronics.

cond-mat.quant-gas↗

arXiv2004

Quantum dynamics of two capacitively coupled superconducting islands via Josephson junctions

In this paper, we consider a system consisting of two capacitively coupled superconducting islands via Josephson junctions. We show that it can be reduced to two coupling harmonic oscillators under certain conditions, and solved exactly in terms of a displacing transformation, a beam-splitter-like transformation, and a squeezing transformation. It is found that the system evolves by a rotated-squeezed-coherent state when the system is initially in a coherent state. Quantum dynamics of the Cooper pairs in the two superconducting islands is investigated. It is shown that the number of the Cooper pairs in the two islands evolves periodically.

cond-mat.mes-hall↗

arXiv2002

Electronic transmission of a nanowire partly irradiated under terahertz electromagnetic field

We theoretically study the electronic transport of a nanowire partly irradiated under an external terahertz (THz) electromagnetic field. Although the electrons in the ballistic nanowires only suffer lateral collision with photons the reflection of electrons also takes place in this partly irradiated case. Using free-electron model and scattering matrix approach we showed that at resonance there exists a step decrement of 50 percent for the transmission probability as the amplitude of field increases to a certain volume. And the coherent structure of transmission for the system apparently appears when the field irradiate the middle part of nanowire only. This sensitive transmission property of the system may be used in the THz detection.

cond-mat.mes-hall↗