Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi

Abstract

Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range 300 − 800 K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters of a = b = c = 4.445 Å . The measured values of Seebeck coefficient (S) shows the non-monotonic behaviour in the studied temperature range with the value of ∼ −81 μV/K at room temperature. The |S| first increases till 560 K (∼ −93 μV/K) and then decreases up to 800 K (∼ −84 μV/K) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity, σ (thermal conductivity, κ) shows the monotonic decreasing (increasing) behaviour with the values of ∼5.2×105 (12.1 W/m-K) and ∼3.6×105 (14.2 W/m-K) Ω−1 m−1 at 300 K and 800 K, respectively. The κ exhibits the temperature dependency as, κ ∝ T0.16 . The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the |S| above 560 K and change in the slope of σ around 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time (τ ) is computed by comparing the experimental σ with calculated σ/τ and it shows temperature dependency of 1/T0.35 . Further this value of τ is used to calculate the temperature dependent electronic part of thermal conductivity (κe) and it gives fairly good match with the experiment. Present study suggests that electronic band-structure obtained from DFT provides reasonably good estimate of the transport coefficients of CoSi in the high temperature region of 300 − 800 K.

Topological Spin Semimetal Feature in a Fully Compensated Ferrimagnet CoRuVSi

“…Figure shows the T -dependence of the Seebeck coefficient ( S ) (left y scale) along with the power factor ( S 2 σ) (right y -scale). S shows a sublinear variation with T , which is typically seen in semimetals. , The negative slope of S with T corresponds to electron-driven thermopower, which again reveals two-carrier conduction in this system. The linear behavior of S suggests the dominance of diffusion thermopower.…”

“…S shows a sublinear variation with T, which is typically seen in semimetals. 29,30 The negative slope of S with T corresponds to electron-driven thermopower, which again reveals two-carrier conduction in this system. The linear behavior of S suggests the dominance of diffusion thermopower.…”

CoRuVSi: A potential candidate for spin semimetal with promising spintronic and thermoelectric properties

“…Figure 7 shows the T-dependence of the Seebeck coefficient (S) (left y-scale) along with the power factor (S 2 σ) (right y-scale). S shows a sub-linear variation with T, which is typically seen in semimetals [28,29] The negative slope of S with T corresponds to electron-driven thermopower, which again reveals two-carrier conduction in this system. The linear behavior of S suggests the dominance of diffusion thermopower.…”

Disorder-Induced Magnetotransport Anomalies in Amorphous and Textured Co1–xSix Semimetal Thin Films

“…Furthermore, when the silicon content is increased to x = 0.57 in amorphous Co 1– x Si x the charge carrier density drops by nearly 2 orders of magnitude. Taken together, the drop in charge carrier density and the change in carrier type to full electron-like as a function of x could be interpreted as a transition through a band touching point, crossed upon silicon doping the cobalt bands at the Fermi energy …”

“…Taken together, the drop in charge carrier density and the change in carrier type to full electron-like as a function of x could be interpreted as a transition through a band touching point, crossed upon silicon doping the cobalt bands at the Fermi energy. 72 An evident effect of the film microstructure is that textured Co 1−x Si x films present a Hall mobility on the order of μ H ≈ 20 cm 2 /V s, which is nearly 2 orders of magnitude larger than in the case of amorphous Co 1−x Si x films having μ H ≈ 0.22 cm 2 /V s. As expected, both amorphous and textured Co 1−x Si x films feature lower values of Hall mobilities as compared to CoSi single crystals 17 (μ H ≈ 230−7300 cm 2 /V s). We note that the amorphous Co 0.43 Si 0.57 film presents a higher mobility μ H ≈ 7.5 cm 2 /V s at 2 K as compared to the other amorphous samples.…”