arXiv subjects

Prakash Pandey

Publications and source records attributed to Prakash Pandey.

7 recordsLinked to original sources

arXiv2026

Multiple topological electronic and phononic quasiparticle excitations in hexagonal TTe (T=Hf, Zr & Ti) crystals

The exploration of topological fermions and bosons marks a new chapter in condensed matter physics, unveiling rich and unconventional phenomena. Particularly in quantum field theory, exotic quasiparticle excitations such as Dirac and Weyl fermions can serve as direct analogs, and their recent experimental realizations have sparked significant interest in these topological quasiparticles. Although there are various reports on the coexistence of unconventional fermionic quasiparticles such as spin-1/2 (type-I, type-II, & type-III), spin-1 (threefold degeneracy), nodal line (type-I, type-II, & type-III) and others, reports on the simultaneous presence of such quasiparticles in both electronic and phononic spectra within a single material remain extremely limited. Herein, using state-of-theart ab initio calculations, we propose the HfTe class of materials, which hosts coexisting type-I, type-II, and type-III Weyl and nodal line phases, along with pseudospin-1/spin-1 quasiparticles in both electronic and phononic states. We have found that these excitations are robust against variations in exchange-correlation functionals, spin-orbit coupling, and lattice parameters, confirming that multiple topological phases in this class of materials are likely to be observed experimentally.

cond-mat.mtrl-sci↗

arXiv2025

Strain-tunable type-II to type-III & Gimbal nodal line transition in Imm2-phase of Cu$_2$SnS$_3$: An ab-initio study

Topological nodal line semimetals (NLSMs) represent an intriguing quantum phase, opening new avenues in materials science for practical applications such as anisotropic transport devices, high-mobility conductors, unconventional thermoelectrics, and nonlinear optical devices. Recently, Cu$_2$SnS$_3$ has been theoretically proposed as a type-II NLSM, with its Fermi surface containing only one nodal ring. Here, we demonstrate how uniaxial, equi-biaxial, and equi-triaxial strains affect the nodal line state of the $Imm2$-phase of Cu$_2$SnS$_3$ by using state-of-the-art ab-initio calculations. Under the application of uniaxial compressive strain (UCS) along the a-direction, the plane of the nodal line evolves from the $k_x$-$k_z$ to $k_y$-$k_z$ for 6\%$\leq$UCS$\leq$8\%. In contrast, under uniaxial tensile strain (UTS), the nodal line remains in the ($k_x$-$k_z$) plane across the entire studied range of UTS. Interestingly, on the application of equi-biaxial tensile strain (EBTS) along a-b (a-c) directions, it hosts only one nodal ring below 8\% ($<$6\%), which further evolves into three (seven) nodal-ring for EBTS of 8\% (6\%$\leq$EBTS$\leq$8\%). Upon the application of EBTS along a-c directions, we found two sets of three mutually orthogonal, intersecting nodal loops (topological gimbals). Apart from this, under the application of equi-biaxial compressive strain (EBCS) along the a-b (a-c) directions, it exhibits only one nodal ring up to 8\% (7\%). Beyond this, the nodal line completely vanishes and does not reappear at higher values of EBCS. Under equi-triaxial tensile strain (ETTS), Cu$_2$SnS$_3$ exhibits only one nodal-ring $<$6\%, which subsequently transforms into five nodal-ring for 6\%$\leq$ETTS$\leq$8\%. However, under the application of equi-triaxial compressive strain (ETCS), as in EBCS, only one nodal line exists up to 6\% ETCS.

cond-mat.mtrl-sci↗

arXiv2025

Revisiting the Topological Nature of TaIrTe4, SrSi2, and Cu2XY3: An ab-initio Investigation

Several topological electronic materials have been theoretically predicted, leading to a comprehensive catalog systematically characterized by their band crossings. Researchers have attempted to experimentally verify the topological nature of some materials from the present catalogs, but not all efforts have yielded positive results. Here, we introduce a possible reason for the discrepancies between theoretical and experimental results. In this direction, firstly we have revisited the nature of the well-known topological materials TaIrTe$_4$ and SrSi$_2$ using \textit{state-of-the-art ab-initio} calculations, and found additional Weyl points in both materials that were missing in previously reported studies. Then we have verified the recently predicted topological states of the \textit{Imm2}-phase of Cu$_2$XY$_3$ (X=Si, Ge, Sn \& Y=S, Se, Te). Contrary to previously reported results, we did not find any Weyl points or nodal arcs in Cu$_2$SnTe$_3$. Notably, our theoretical results reveal that Cu$_2$SiTe$_3$, Cu$_2$GeTe$_3$ and Cu$_2$GeSe$_3$ each host four small nodal rings, eight Weyl points, and eight nodal arcs, respectively, which differ from previous studies. Considering Cu$_2$SnS$_3$ as an example, we have also investigated the robustness of the topological phase against local strain. Our study provides insights into the inconsistencies between theoretical predictions and experimental results, and demonstrates how the topological phase is sensitive to changes in lattice parameters, atomic positions, and exchange-correlation functionals.

cond-mat.mtrl-sci↗

arXiv2025

Realization of strain induced multiple topological phases in Cu$_2$SnS$_3$: An $ab$-$initio$ study

The search of multiple topological phases (TPs) and their transitions by tuning different parameters through chemical substitutions, electric field, magnetic field, strain and Floquet engineering, etc has garnered a widespread attention in recent time. In spite of great effort, the observations of multiple TPs in a single material and multiple TP transitions in the presence of one parameter remain elusive. Here we demonstrate the presence of multiple TPs and their transitions with uniaxial compressive strain (UCS) in orthorhombic Cu$_2$SnS$_3$ by using $state$-$of$-$the$-$art$ $ab$-$initio$ calculations. In the absence of spin-orbit coupling (SOC), the Cu$_2$SnS$_3$ exhibits a single (type-II) nodal-ring and in the presence of SOC, it hosts Weyl phase with seven Weyl points (three at $\Gamma$ and four at general positions) along with nodal arcs. On the application of UCS, it remains type-II nodal-ring $<5.5$\%, which further evolves into type-III nodal-ring for $5.5\% \leq$ UCS $<5.6$\%. Interestingly, at 5.6\% of UCS, it shows Weyl phase with four Weyl nodes even in the absence of SOC. All the above-mentioned seven Weyl points persist below $5$\% of UCS. For 5\% $\leq$ UCS $<5.6$\%, four Weyl points (at general positions) disappear and nodal-arcs remain intact in all the studied range of UCS. The TPs observed in the absence of SOC appears to arise due to the presence of strain driven topological flat band, which is typically reported to be seen in kagome and Lieb lattices.

cond-mat.mtrl-sci↗

arXiv2024

PH-NODE: A DFPT and finite displacement supercell based python code for searching nodes in topological phononic materials

Exploring the topological physics of phonons is fundamentally important for understanding various practical applications. Here, we present a density-functional perturbation theory and finite displacement supercell based Python 3 software package called PH-NODE for efficiently computing phonon nodes present in real material through a first-principle approach. The present version of the code is interfaced with the WIEN2k, Elk, and ABINIT packages. In order to benchmark the code, four different types of materials are considered, which include (i) FeSi, a well-known double-Weyl point; (ii) LiCaAs, a half-Heusler single-type-I Weyl topological phonon (TP); and (iii) ScZn, coexisting nodal-line and nodal-ring TPs; (iv) TiS, six pairs of bulk Weyl nodes. In FeSi, the node points are found at $Γ$(0, 0, 0) and R(0.5, 0.5, 0.5) high symmetric points. Also, there are 21 energy values at which the node points are situated, corresponding to the full Brillouin Zone. For LiCaAs, the previously reported literature claims that there is a node point along the W-X high symmetry direction between the highest longitudinal acoustic and the lowest transverse optical branch, while in our DFT calculations, a gap of 0.17 meV is found. Furthermore, ScZn hosts six nodal-ring TPs phonons at the boundary planes of the Brillouin Zone in the vicinity of the M high-symmetric point. In addition to this, straight-line TPs are also found along the $Γ$-X and $Γ$-R high symmetric directions. Moreover, for TiS, six weyl node points (WP1, WP2, WP3, WP4, WP5 and WP6) are found along H-K high-symmetric direction. The results obtained from the PH-NODE code are in good agreement with the experimentally and theoretically reported data for each material.

cond-mat.mtrl-sci↗

arXiv2023

Ab initio investigation of the lattice dynamics and thermophysical properties of BCC Vanadium and Niobium

In the present work, we have performed the phonon dispersion calculations of body-centered cubic Vanadium (V) and Niobium (Nb) with the supercell approach using different supercell size. Using DFT method, the calculated phonon spectra of V and Nb are found to be in a good agreement with the available experimental data. Our calculated results show a \enquote{dip}-like feature in the longitudinal acoustic phonon mode along the $Γ$-H high symmetric path for both transition metals in the case of supercell size 4$\times$4$\times$4. However, in supercell size 2$\times$2$\times$2 and 3$\times$3$\times$3, the \enquote{dip}-like feature is not clearly visible. In addition to this, thermodynamical properties are also computed, which compare well with the experimental data. Apart from this, the phonon lifetime due to electron-phonon interactions ($τ_{\rm{eph}}^{\rm{ph}}$) and phonon-phonon interactions ($τ_{\rm{ph}}^{\rm{ph}}$) are calculated. The effect of phonon-phonon interactions (PPI) is studied by computing the average phonon lifetime for all acoustic branches. The value of $τ_{\rm{eph}}^{\rm{ph}}$ of V (Nb) is found to be 23.16 (24.70)$\times 10^{-15}$ s at $100$ K, which gets decreased to 1.51 (1.85)$\times 10^{-15}$ s at 1000 K. The $τ_{\rm{ph}}^{\rm{ph}}$ of V (Nb) is found to be 8.59 (18.09)$\times 10^{-12}$ and 0.83 (1.76)$\times 10^{-12}$ s at 100 and 1000 K, respectively. Nextly, the lattice thermal conductivity is computed using linearized phonon Boltzmann equation. The present work suggests that studying the variation of phonon dispersion with supercell size is crucial for understanding the phonon properties of solids accurately.

cond-mat.mtrl-sci↗

arXiv2023

Investigating the effect of electronic correlation on transport properties and phononic states of Vanadium

In the present work, we have tried to investigate the importance of electronic correlation on transport properties and phononic states of Vanadium (V). The temperature-dependent electrical resistivity ($ρ$) and electronic part of thermal conductivity ($κ_e$) due to electron-electron interactions (EEIs) and electron-phonon interactions (EPIs) are computed. The values of $ρ$ due to EEIs are found to be extremely small in comparison to $ρ$ due to EPIs. For instance, at 300 K, the calculated value of $ρ$ due to EEIs (EPIs) is $\sim$ 0.859$\times10^{-3}$ ($\sim$ 0.20) $μΩ$m. The magnitudes of $κ_e$ due to EPIs are found to be in good agreement with the experimental results. These observations indicate the negligible importance of EEIs to these quantities for V. However, at 300 K, the value of Seebeck coefficient ($S$) at DFT+DMFT level ($\sim$ -0.547 $μ$VK$^{-1}$) is found to be entirely different than at DFT level ($\sim 7.401$ $μ$VK$^{-1}$). Also, the DFT+DMFT value of $S$ at 300 K is in good match with the available experimental data (-1.06 $μ$VK$^{-1}$, 1.0 $μ$VK$^{-1}$). Apart from this, the study of phononic states at DFT and DFT+DMFT level is performed. The obtained phononic band structure and phonon DOS at DFT+DMFT differ to a good extent from that at DFT. The maximum energy of phononic state obtained at DFT (DFT+DMFT) is $\sim$ 33.83 ($\sim$ 35.15) meV, where the result of DFT+DMFT is obtained more closer to the experimental data (35.15, 36.98 & 41.77 meV). These results highlight the importance of electronic correlation on $S$ & phononic states of simple correlated V metal.

cond-mat.str-el↗