Magnetotransport Of Weyl Semimetals Research Articles

Magnetotransport of Weyl semimetals with tilted Dirac cones

Weyl semimetals (WSM) exhibit chiral anomaly in their magnetotransport due to broken conservation laws. Here, we analyze the magnetotransport of WSM in the presence of the time-reversal symmetry-breaking tilt parameter. The analytical expression for the magnetoconductivity is derived in the small tilt limit using the semiclassical Boltzmann equation. We predict a planar Hall current which flows transverse to the electric field and in the plane containing magnetic and electric fields and scales linearly with the tilt parameter. A tilt-induced transverse conductivity is also present in the case where the electric and magnetic fields are parallel to each other, a scenario where the conventional Hall current completely vanishes.

Thermal and gravitational chiral anomaly induced magneto-transport in Weyl semimetals

Quantum anomalies in Weyl semimetal (for either ${\bf E}\cdot{\bf B} \neq 0$ or ${\bf \nabla}T\cdot{\bf B} \neq 0$) leads to chiral charge and energy pumping between the opposite chirality nodes. This results in chiral charge and energy imbalance between the Weyl nodes which manifests in several intriguing magneto-transport phenomena. Here, we investigate the role of electrical-, thermal-, and gravitational chiral anomaly on magneto-transport in Weyl semimetals. We predict the planar Ettinghausen and Righi-Leduc effect to be a distinct signature of these quantum anomalies. We also demonstrate a significant enhancement in the thermo-electric conductivity, Seebeck effect, Nernst effect and thermal conductivity with increasing temperature. Interestingly, this anomaly induced transport violates the Wiedemann-Franz law and Mott relation.

Magnetotransport of Weyl semimetals with \u21242 topological charge and chiral anomaly

We calculate the magnetoconductivity of the Weyl semimetal with ℤ2 topological charge and chiral anomaly utilizing the recently developed hydrodynamic theory. The system in question will be influenced by magnetic fields connected with ordinary Maxwell and the second U(1)-gauge field, which couples to the anomalous topological charge. The presence of chiral anomaly and ℤ2 topological charge endow the system with new transport coefficients. We start with the linear perturbations of the hydrodynamic equations and calculate the magnetoconductivity of this system. The holographic approach in the probe limit is implemented to obtain the explicit dependence of the longitudinal magneto-conductivities on the magnetic fields.

Berry curvature force and Lorentz force comparison in the magnetotransport of Weyl semimetals

Three-dimensional Weyl semimetals have been observed to have negative magnetoresistance (MR) with the magnetic field parallel to the electric field and positive MR with the magnetic field perpendicular to the electric field. It is understood that the negative MR is due to a Berry phase that causes the chiral anomaly, while the positive MR can be understood from a semiclassical transport theory. We solve a semiclassical Boltzmann equation with both the Berry phase and Lorentz force terms present for an arbitrary angle of the applied magnetic field relative to the electric field within the relaxation-time approximation. The plots of the magnetoconductivity show both the Berry phase and Lorentz force effects. For some angles between the electric and magnetic fields, the conductivity has a minimum, where the forces balance each other. The standard semiclassical theory does not show the linear increase in the transverse MR with the magnetic field seen experimentally. By assuming a magnetic-field-dependent transport time, we find the transverse MR increases linearly with the magnetic field. The low-field MR does change from negative to positive as one rotates the magnetic field away from the direction of the electric field. As the magnetic field is increased, we find in some cases the MR starts out negative and then becomes positive. This is consistent with recent experimental data in ${\text{Cd}}_{3}{\text{As}}_{2}$.

Effect of the screened Coulomb disorder on magneto-transport in Weyl semimetals

The observation of negative longitudinal magnetoresistivity (NLMR) in Weyl semimetals has gained strong support in recent experiments. It is believed that charged impurities play an important role in the measurement of NLMR. We thus employ a screened Coulomb disorder to model charged impurities and derive a general screening length depending on the magnetic field, chemical potential and temperature. We study the magneto-transport in a two-node Weyl semimetal in which the intra-valley scattering and the inter-valley scattering can be explored simultaneously. We also calculate the effect of the misalignment of the external electric field and the magnetic field on the longitudinal and transverse magnetoconductivities, recovering the experimental observations. We show that the former (latter) is suppressed (enhanced) sensitively with the density of the impurity. This feature makes it hard to observe the NLMR in experiments in the heavy doping case. These results may be exploited to explain the sample-dependent observation of NLMR and deepen our understanding of magneto-transport in Weyl semimetals.

Magnetic description of the Fermi arc in type-I and type-II Weyl semimetals

We consider finite-sized interfaces of a Weyl semi-metal and show that the corresponding confinement potential is similar to the application of a magnetic field. Among the numerous states, which can be labeled by indices n like in Landau levels, the n = 0 surface state describes the Weyl semimetal Fermi arc at a given chemical potential. Moreover, the analogy with a magnetic field shows that an external in-plane magnetic field can be used to distort the Fermi arc and would explain some features of magneto-transport in Weyl semimetals. We derive the Fermi arc for type-I and type-II Weyl semimetals where we deal with the tilt anisotropy by the use of Lorentz boosts. In the case of type-II Weyl semimetals, this leads to many additional topologically trivial surface states at low energy. Finally, we extend the Aharonov-Casher argument and demonstrate the stability of the Fermi arc over fluctuations of the surface potential.

Magnetotransport in Weyl semimetals in the quantum limit: Role of topological surface states

We theoretically study the magnetoconductivity of the Weyl semimetal having a surface boundary under $E$ || $B$ geometry and demonstrate that the topological surface state plays an essential role in the magnetotransport. In the long-range disorder limit where the scattering between the two Weyl nodes vanishes, the conductivity diverges in the bulk model (i.e., periodic boundary condition) as usually expected, since the direct inter-node relaxation is absent. In the presence of the surface, however, the inter-node relaxation always takes place through the mediation by the surface states, and that prevents the conductivity divergence. The magnetic-field dependence becomes also quite different between the two cases, where the conductivity linearly increases in $B$ in the surface boundary case, in contrast to $B$-independent behavior in the bulk-periodic case. This is an interesting example in which the same system exhibits completely different properties in the surface boundary condition and the periodic boundary condition even in the macroscopic size limit. In the short-range regime where the direct intervalley scattering is dominant, the surface states are irrelevant and the conductivity approaches that of the bulk periodic model.

Density of states and magnetotransport in Weyl semimetals with long-range disorder

We study the density of states and magnetotransport properties of disordered Weyl semimetals, focusing on the case of a strong long-range disorder. To calculate the disorder-averaged density of states close to nodal points, we treat exactly the long-range random potential fluctuations produced by charged impurities, while the short-range component of disorder potential is included systematically and controllably with the help of a diagram technique. We find that for energies close to the degeneracy point, long-range potential fluctuations lead to a finite density of states. In the context of transport, we discuss that a self-consistent theory of screening in magnetic field may conceivably lead to non-monotonic low-field magnetoresistance.