论文标题
在二维系统中，非线性磁转运与零点合并
Nonlinear magnetotransport in a two-dimensional system with merging Dirac points
论文作者
论文摘要
我们使用半磁场（$ b $）的影响，研究二维间隙半迪拉克系统的线性，二阶非线性（NL）电流和电压响应，并使用半效的磁场（$ b $）合并了dirac节点。我们研究了响应中的带状几何量（如浆果曲率和轨道磁矩）在$ b $中的线性顺序中的效果。我们得出了线性磁磁性的精确分析表达，第二谐波NL异常大厅（NAH）以及异常的速度和Lorentz力诱导的（NAL）电导率（NAL）电导率，揭示其对费米能量的依赖性和GAP参数$Δ_0$。对于$Δ_0> 0 $，费米表面拓扑会在特定的费米能量上发生变化，该拓扑会通过扭结反映在电导率的性质中。发现NAL和NAH电导率的比率与$Δ_0$无关，并且与费米能量成反比。 NL DC电流取决于费米能，磁场，电磁波极化。在存在磁场的情况下，NL DC电流载体可以在Fermi能量的变化时旋转大角度。对于高费米能量，NL DC电流几乎沿着$ y $轴沿$ x $偏振和低频圆形极化光线进行定向，而对于高频循环圆形极化光，它与接近$ x $轴的一致。 NL DC电流的这些方向主要由沿$ x $方向系统的镜像对称性控制。此外，我们还通过沿$ x $和$ y $方向应用电流来研究系统的NL电压响应。该系统在NL电阻率的$ b $依赖性中表现出不对称性，可以用作实验相关的频带几何量和在此类系统中合并DIRAC节点的签名。
We study the linear, second-order nonlinear (NL) current and voltage responses of a two-dimensional gapped semi-Dirac system with merging Dirac nodes along the $x$ direction under the influence of a weak magnetic field ($B$), using the semiclassical Boltzmann formalism. We investigate the effect of band geometric quantities like Berry curvature and orbital magnetic moment in the responses up to linear order in $B$. We derive exact analytical expressions of the linear magnetoconductivities, second-harmonic NL anomalous Hall (NAH), and anomalous velocity and Lorentz force induced (NAL) conductivities, unveiling their dependence on Fermi energy and a gap parameter $δ_0$. For $δ_0 > 0$, the Fermi surface topology changes at a particular Fermi energy, which is reflected in the nature of conductivities through a kink. The ratio of NAL and NAH conductivities is found to be independent of $δ_0$ and inversely related to Fermi energy. The NL dc current exhibits distinct orientations depending on the Fermi energy, magnetic field, polarization of the electromagnetic wave. In the presence of magnetic field, the NL dc current vector can be rotated through large angles on variation of Fermi energy. For high Fermi energies, the NL dc current is directed nearly along the $y$-axis for $x$-polarized and low-frequency circularly polarized light, whereas it aligns close to $x$-axis for high-frequency circularly polarized light. These orientations of the NL dc current are predominantly governed by the mirror symmetry of the system along the $x$ direction. Additionally, we also study the NL voltage responses of the system by applying current along the $x$ and $y$ directions. The system exhibits asymmetry in the $B$-dependencies of the NL resistivities, which may serve as an experimentally relevant signature for band geometric quantities and merging Dirac nodes in such systems.
