Linear and nonlinear optical responses in the chiral multifold semimetal RhSi

Chiral topological semimetals are materials that break both inversion and mirror symmetries. They host interesting phenomena such as the quantized circular photogalvanic effect (CPGE) and the chiral magnetic effect. In this work, we report a comprehensive theoretical and experimental analysis of the linear and nonlinear optical responses of the chiral topological semimetal RhSi, which is known to host multifold fermions. We show that the characteristic features of the optical conductivity, which display two distinct quasi-linear regimes above and below 0.4 eV, can be linked to excitations of different kinds of multifold fermions. The characteristic features of the CPGE, which displays a sign change at 0.4 eV and a large non-quantized response peak of around 160 μA/V2 at 0.7 eV, are explained by assuming that the chemical potential crosses a flat hole band at the Brillouin zone center. Our theory predicts that, in order to observe a quantized CPGE in RhSi, it is necessary to increase the chemical potential as well as the quasiparticle lifetime. More broadly, our methodology, especially the development of the broadband terahertz emission spectroscopy, could be widely applied to study photogalvanic effects in noncentrosymmetric materials and in topological insulators in a contact-less way and accelerate the technological development of efficient infrared detectors based on topological semimetals.

Bi and Zn co-doped SnTe thermoelectrics: interplay of resonance levels and heavy hole band dominance leading to enhanced performance and a record high room temperature ZT

Interplay of resonance levels in Bi–Zn co-doped SnTe thermoelectrics showcasing a record high room temperature and average ZT.

Magnetoelastoresistance in WTe2: Exploring electronic structure and extremely large magnetoresistance under strain

Strain describes the deformation of a material as a result of applied stress. It has been widely employed to probe transport properties of materials, ranging from semiconductors to correlated materials. In order to understand, and eventually control, transport behavior under strain, it is important to quantify the effects of strain on the electronic bandstructure, carrier density, and mobility. Here, we demonstrate that much information can be obtained by exploring magnetoelastoresistance (MER), which refers to magnetic field-driven changes of the elastoresistance. We use this powerful approach to study the combined effect of strain and magnetic fields on the semimetallic transition metal dichalcogenideWTe2. We discover that WTe2shows a large and temperature-nonmonotonic elastoresistance, driven by uniaxial stress, that can be tuned by magnetic field. Using first-principle and analytical low-energy model calculations, we provide a semiquantitative understanding of our experimental observations. We show that inWTe2, the strain-induced change of the carrier density dominates the observed elastoresistance. In addition, the change of the mobilities can be directly accessed by using MER. Our analysis also reveals the importance of a heavy-hole band near the Fermi level on the elastoresistance at intermediate temperatures. Systematic understanding of strain effects in single crystals of correlated materials is important for future applications, such as strain tuning of bulk phases and fabrication of devices controlled by strain.

Термоэлектрические характеристики сильно легированного теллурида свинца p-типа при разной глубине зоны тяжелых дырок

The full set of thermoelectric parameters of heavily doped p -PbTe in the temperature range of 300–1200 K at an acceptor doping level of N _ a = 1 × 10^19–4 × 10^20 cm^–3 and a heavy-hole band depth ranging from 0.36 to 0.7 eV is calculated. The figure-of-merit value Z is found to be highly sensitive to the doping level and increased by a factor of 1.5 with an increase in the dopant concentration from 1 × 10^19 to 5 × 10^19 cm^–3; the maximum Z value is found to correspond to N _ a = (1–2) × 10^20 cm^–3. It is demonstrated that the change in the heavy-hole band depth leads to a noticeable shift of the Z maximum position along the temperature axis without noticeable Z maximum variation. The temperature corresponding to the maximum Z value is similar to that at which the top of the light-hole band crosses the Fermi level. The maximum calculateded ZT value is shown to be 1.64. At a heavy-hole band depth of 0.5 eV, the calculated results agree well with the available experimental data.

Analysis of EL Emitted by LEDs on Si Substrates Containing GeSn/Ge Multi Quantum Wells as Active Layers

We analyzed multi quantum well light emitting diodes, consisting of ten alternating GeSn/Ge-layers, were grown by molecular beam epitaxy on Si. The Ge barriers were 10 nm thick and the GeSn wells were grown with 7% Sn and thicknesses between 6 and 12 nm. Despite the high threading dislocation density of 109to 1010cm−2the electroluminescence spectra measured at 300 and 80 K yield a broad and intensive luminescence band. Deconvolution revealed three major lines produced by the GeSn wells that can be interpreted in terms of quantum confinement. Biaxial compressive strain causes a splitting of light and heavy holes in the GeSn wells. We interpret the three lines to represent two direct lines, formed by transitions with the light and heavy hole band, respectively, andan indirect line.