Enhancing Thermopower and Nernst Signal of High‐Mobility Dirac Carriers by Fermi Level Tuning in the Layered Magnet EuMnBi₂

Abstract

In the last 15 years, conducting materials, whose low energy excitation exhibits linear energy-momentum dispersion of relativistic Dirac fermions, have attracted much attention due to

Weyl Semimetal States Generated Extraordinary Quasi‐Linear Magnetoresistance and Nernst Thermoelectric Power Factor in Polycrystalline NbP

“…Various studies in NbP, TaP, NbAs, and TaAs have reported prominent properties of MR in the range of 10 4 %-10 6 % [9,16,18,19,37] as well as Nernst thermopower (S xy ) of ≈1 × 10 3 μV K -1 , [16,21,23] which represent remarkable progresses among different types of topological semimetals. [35,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Taking NbP as the example, the MR of single-crystal NbP reaches an extremely large value of 8.5 × 10 5 % at 1.85 K in a magnetic field of 9 T, [9,37] which is ascribed to the interplay of overlapped conduction and valence bands, linear band dispersion and ultra-high carrier mobility (μ) of 5 × 10 6 cm 2 V -1 s -1 . The ultra-high μ and the effective compensation of electrons and holes are two critical factors responsible for the prominent S xy in NbP, and thus, a usually large Nernst thermopower (S xy ) exceeding 800 μV K -1 could be obtained at 9 T and 109 K, [21] leading to a very large Nernst thermoelectric power factor (PF xy ).…”

High-field Studies on Layered Magnetic and Polar Dirac Metals: Novel Quantum Transport Phenomena Coupled with Spin-valley Degrees of Freedom

“…More recently, it has been revealed that the exchange coupling strongly affects the thermoelectric phenomena (Seebeck and Nernst effects) as well 56 . These facts indicate that various electrical and thermal transport phenomena are tunable by controlling the Dirac band (splitting) via the magnetic Eu layers in this material.…”

“…We have also demonstrated the control of the spin-valley state for BaMnX 2 via the chemical substitution of the X site as a result of the modulation of the lattice distortion and spin-orbit coupling. Furthermore, the partial substitution of the divalent A site with a trivalent one in the block layer leads to electron doping in the Dirac fermion layer, enabling Fermi level tuning across the charge neutral point (not reviewed here in detail) 56 . In addition to magnetic field and chemical substitution, it has been recently predicted that mechanical strain could also significantly affect the band structure and/or topology owing to the high sensitivity to lattice distortion 100 .…”

Effect of Cu Doping on Structure and Physical Properties in the Antiferromagnetic Dirac Semimetal CaMnBi2

“…Furthermore, the [MnBi 4 ] ([MnSb 4 ]) tetrahedral layers in the structure also offer an arena to investigate the interplay between magnetic order and topological properties . Both density functional theory and angle-resolved photoemission spectroscopy demonstrated the anisotropic Dirac cones in momentum space for A MnBi 2 and A MnSb 2 . ,, This intriguing band structure leads to a series of novel quantum properties including giant magnetoresistance (MR), − magnetothermopower, − valley-selective interlayer conduction, and spin-valley locking, which are of relevance for designing new-generation electronic devices with high performance.…”