Physics of large thermoelectric power factors in SnSe nanoflakes in mid-temperature range.

We have theoretically investigated the underlying physics of observed high electrical conductivity (), simultaneous increase of σ and Seebeck coefficient () with temperature, and large power factors (PFs) in nominally undoped SnSe nanoflakes sintered at different temperatures, reported recently in Mandava(2022155710). Given the fact that S and σ show unusual temperature trends and that the undoped SnSe samples are highly porous and disordered, the conventional Boltzmann theory does not appear to be an appropriate model to describe their transport properties. We have, instead, used a strong disorder model based on percolation theory where charge and energy transport take place through hopping between localized states to understand these observations.

Quantum fluctuation effects on the ordered moments in a two dimensional frustrated ferrimagnet.

We propose a novel two-dimensional (2D) frustrated quantum spin-1/2 anisotropic Heisenberg model with alternating ferromagnetic and antiferromagnetic magnetic chains along one direction and antiferromagnetic interactions along the other. The (mean-field) ground state is ferrimagnetic in certain range of the interaction space. Spin-wave theory analysis of the reduction of ordered moments at inequivalent spin sites and the instability of the spin waves suggest a quantum phase transition which has the characteristics of both the frustrated 2D antiferromagnetic= 1/2 (,) model and 1D= 1,= 1/2 quantum ferrimagnetic model.

Coexistence and Interaction of Spinons and Magnons in an Antiferromagnet with Alternating Antiferromagnetic and Ferromagnetic Quantum Spin Chains.

In conventional quasi-one-dimensional antiferromagnets with quantum spins, magnetic excitations are carried by either magnons or spinons in different energy regimes: they do not coexist independently, nor could they interact with each other. In this Letter, by combining inelastic neutron scattering, quantum Monte Carlo simulations, and random phase approximation calculations, we report the discovery and discuss the physics of the coexistence of magnons and spinons and their interactions in Botallackite-Cu_{2}(OH)_{3}Br. This is a unique quantum antiferromagnet consisting of alternating ferromagnetic and antiferromagnetic spin-1/2 chains with weak interchain couplings.

Probing the Electronic Structure of Hybrid Perovskites in the Orientationally Disordered Cubic Phase.

Hybrid organic-inorganic lead halide perovskites are projected as new generation photovoltaic and optoelectronic materials with improved efficiencies. However, their electronic structure so far remains poorly understood, particularly in the orientationally disordered cubic phase. We performed electronic structure investigations using angle-resolved photoemission spectroscopy on two prototypical samples (MAPbBr and MAPbCl) in their cubic phase, and the results are compared with the calculations within two theoretical models where MA is orientationally (1) disordered (MA ion is replaced by spherically symmetric Cs ion) and (2) ordered (MA oriented along (100) direction) but keeping the symmetry of the unit cell cubic.

Compositional Tailoring for Realizing High Thermoelectric Performance in Hafnium-Free n-Type ZrNiSn Half-Heusler Alloys.

Compositional tailoring enables fine-tuning of thermoelectric (TE) transport parameters by synergistic modulation of electronic and vibrational properties. In the present work, the aspects of compositionally tailored defects have been explored in ZrNiSn-based half-Heusler (HH) TE materials to achieve high TE performance and cost effectiveness in n-type Hf-free HH alloys. In off-stoichiometric Ni-rich ZrNiSn alloys in a low Ni doping limit ( < 0.