[论文解读] Thermo-Magneto-Electric Transport through a Torsion Dislocation in a Type I Weyl Semimetal

Daniel A. Bonilla|arXiv (Cornell University)|Nov 5, 2021

Topological Materials and Phenomena参考文献 44被引用 8

一句话总结

本研究 investigates thermo-magneto-electric transport in a type I Weyl semimetal nanojunction with a torsional dislocation, modeling strain via a gauge field and lattice mismatch via a repulsive delta-shell potential (RDSP). In the presence of an axial magnetic field, the system exhibits chiral valley-polarized current and quantized conductance due to node-dependent Landau levels, with predicted high thermopower and a large figure of merit (ZT > 10) at low temperatures, indicating strong potential for thermoelectric applications.

ABSTRACT

Herein, we study electronic and thermoelectric transport in a type I Weyl semimetal nanojunction, with a torsional dislocation defect, in the presence of an external magnetic field parallel to the dislocation axis. The defect is modeled in a cylindrical geometry, as a combination of a gauge field accounting for torsional strain and a delta-potential barrier for the lattice mismatch effect. In the Landauer formalism, we find that due to the combination of strain and magnetic field, the electric current exhibits chiral valley-polarization, and the conductance displays the signature of Landau levels. We also compute the thermal transport coefficients, where a high thermopower and a large figure of merit are predicted for the junction.

研究动机与目标

• To investigate the interplay of torsional strain, magnetic fields, and lattice mismatch in a type I Weyl semimetal nanojunction.
• To model the effects of mechanical strain as a gauge field and lattice mismatch as a repulsive delta-shell potential (RDSP).
• To analyze how these defects influence electronic and thermoelectric transport in the presence of an axial magnetic field.
• To evaluate the thermoelectric performance, particularly the figure of merit (ZT), for potential energy harvesting applications.

提出的方法

• Model the Weyl semimetal using a free Hamiltonian with Weyl fermion dispersion near nodal points with chirality ξ = ±1.
• Represent torsional strain via a gauge field AS = BS/2(−yê1 + xê2), combining with an external magnetic field B0 to form an effective node-dependent pseudo-magnetic field Bξ = B0 + ξBS.
• Incorporate lattice mismatch at the dislocation boundary using a repulsive delta-shell potential VRD(r) = V0δ(r − a), inducing chiral spinor rotation across r = a with angle α = V0/(¯hvF).
• Apply the Landauer formalism to compute energy-dependent transmission and conductance, using scattering phase shifts and differential cross-sections.
• Derive analytical expressions for thermal transport coefficients (Seebeck, thermal conductance, Lorenz number) from the Landauer-Büttiker formalism.
• Use dimensionless scaling groups involving material parameters (vF, a, L, W) and external fields to generalize results across Weyl semimetal materials.

实验结果

研究问题

• RQ1 How does the combination of torsional strain and an axial magnetic field affect the electronic transport in a Weyl semimetal nanojunction?
• RQ2 What is the role of the repulsive delta-shell potential (RDSP) in modifying the transmission and conductance, particularly in relation to chiral tunneling?
• RQ3 How do the thermoelectric coefficients—Seebeck, thermal conductance, and figure of merit—depend on temperature, magnetic field, and lattice mismatch strength?
• RQ4 Can the system exhibit 'magic angles' where the RDSP barrier becomes transparent due to Klein-like tunneling effects?
• RQ5 What is the predicted performance of the system in terms of thermoelectric efficiency, especially the figure of merit ZT?

主要发现

• The electric current exhibits chiral valley-polarization due to the node-dependent effective magnetic field Bξ = B0 + ξBS, breaking time-reversal symmetry.
• Conductance shows discrete peaks at low temperatures corresponding to relativistic Landau levels with energy Eξλ,n = λ¯hvF√(2n|Bξ|/˜φ0 + k2z), confirming quantized transport.
• The RDSP induces a periodic transmission dependence on V0, with transparency at 'magic angles' where tan(V0/¯hvF) = 0, indicating Klein tunneling in a cylindrical geometry.
• The Seebeck coefficient reaches values up to S ≈ 10 kB/e at T ≈ 2.5¯hvF/kBa, indicating strong thermopower enhancement.
• The thermal conductance κ is on the order of 6.6 W/mK for Cd3As2 parameters, consistent with experimental ranges (3–25 W/mK).
• The figure of merit ZT exceeds 10 at low temperatures (T ≈ 2.5¯hvF/kBa), with optimal performance at θ = 15° and α = 3π/4, suggesting high efficiency for thermoelectric energy harvesting.