Polaronic Conductivity in Cr₂Ge₂Te₆ Single Crystals

Abstract

Intrinsic 2D ferromagnetic semiconductors are an important class of materials for spin-charge conversion applications. Cr 2 Ge 2 Te 6 retains long-range magnetic order in the bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, a series of structural, magnetic, X-ray scattering, electronic, thermal transport and first-principles calculation studies are performed, which reveal that localized electronic charge carriers in Cr 2 Ge 2 Te 6 are dressed by the surrounding lattice and are involved in polaronic transport via hopping that is observed via magnetocrystalline anisotropy. This opens the possibility for manipulation of charge transport in Cr 2 Ge 2 Te 6 -based devices by electron-phonon-and spinorbit coupling-based tailoring of polaron properties.

Spin‐Phonon Scattering‐Induced Low Thermal Conductivity in a van der Waals Layered Ferromagnet Cr2Si2Te6

“…However, the effects of spin-phonon scattering in CST survive at much higher temperatures up to about 200 K, leading to low thermal conductivity appearing within a wide temperature window. Similar effects are also seen in an isostructural sister compound Cr 2 Ge 2 Te 6 [48] (Figure 5d). In CST, The magnetic g factor is highly anisotropic and strongly temperature dependent.…”

“…Similar behavior has been reported earlier, [ 36 ] and also appears in a sister compound Cr 2 Ge 2 Te 6 . [ 48 ] The small values and peculiar temperature dependence of κ are similar to those in amorphous silica (see black triangles in Figure 3a), likely suggesting glass‐like thermal transport. [ 16–21,36,48 ] However, as we will show in Figure , diffuson‐like heat conduction only contributes moderately, and spin‐phonon scattering becomes dominant when magnetic fluctuations appear below 200 K. Further cooling below T c , κ seemingly recovers to typical phonon thermal transport with the familiar T −1 temperature dependence.…”

“…[ 48 ] The small values and peculiar temperature dependence of κ are similar to those in amorphous silica (see black triangles in Figure 3a), likely suggesting glass‐like thermal transport. [ 16–21,36,48 ] However, as we will show in Figure , diffuson‐like heat conduction only contributes moderately, and spin‐phonon scattering becomes dominant when magnetic fluctuations appear below 200 K. Further cooling below T c , κ seemingly recovers to typical phonon thermal transport with the familiar T −1 temperature dependence. A characteristic peak is found around 12 K with κ ≈ 2 W K −1 m −1 , which is the maximum value observed within the entire temperature range studied here.…”

“…[41] This naturally leads to reduced spin-phonon scattering strength, which again enhances 𝜅 tot (B) in the presence of magnetic fields by partially recovering 𝜅 tot (1/𝜏 c ). [24] , c) VI 3 [57] , d) Cr 2 Ge 2 Te 6 [48] , e) 𝛼-RuCl 3 [31] and f) FeCl 2 [58] are from literature. The symbols T c , T N, and T s denote ferromagnetic, antiferromagnetic, and structural transition temperatures, respectively.…”

Exploiting the fraternal twin nature of thermoelectrics and topological insulators in Zintl phases as a tool for engineering new efficient thermoelectric generators

“…It is noted that aside from the Zintl phases, there are other classes of materials that have shown potential for TE applications which include the clathrates, skutterudites, half-Heusler phases, etc. ; 91–99 they will not be discussed in this narrative as other articles have summarized their importance. We also wish to note that some aspects of the relationship between topological insulators and TE materials have already been dealt with in the literature.…”