arXiv subjects

Dinesh Thapa

Publications and source records attributed to Dinesh Thapa.

8 recordsLinked to original sources

arXiv2026

Predicting spin orbit coupling effect in the electronic and magnetic properties of cobalt (Co) doped WSe2 monolayer

The electronic and magnetic properties of cobalt (Co) doped monolayer (ML) tungsten diselenide (WSe2) are investigated using the density functional theory with the on-site Hubbard potential correction (DFT+U) for the localized d orbitals of Co atom taking into account the spin orbit coupling (SOC) interaction. The results show that the substitution of Co at the W sites of ML WSe2 is energetically favorable under Se rich environment. We noticed that the Hund's exchange splitting (ΔH_{ex}) is dominant over the crystal field splitting (Δ_{cf}). The induced magnetic moment due to the Co-doped defect is ~3.00 μ_B per Co atom. The magnetic interaction between two Co atoms at the nearest neighbor separation depends mainly on the concentration of the impurity atoms. The calculated value of curie temperature (TC) is increasing with increasing impurity concentration satisfying the Zener model. Based on the results, it can be proposed that the Co-doped WSe2 monolayer is potential candidate to apply in spintronics, optoelectronics, and magnetic storage devices.

cond-mat.mtrl-sci↗

arXiv2026

Spin selective non-van der Waal electride nature in manganese under ambient pressure

Electrides are an unusual class of ionic materials in which electrons localized in non-nuclear, interstitial regions act as anions within the crystal lattice. Here, we employ first-principles quantum mechanical calculations to investigate the structural, electronic, magnetic, and electride characteristics of elemental manganese (Mn) at an ambient pressure (0 GPa), focusing on its three crystalline phases: cubic ($α$)-Mn ($I\bar{4}3m,no.217$), cubic ($β$)-Mn ($P4_132, no.213$), and hexagonal ($hex$)-Mn ($P6_3/mmc, no.194$). Our calculations reveal pronounced interstitial-electron character in all three phases, accompanied by spin-selective electron localization function (ELF), establishing elemental Mn as a non-van der Waals electride system. Bader charge analysis indicates substantial electron redistribution from the Mn host framework toward the interstitial anionic-electron (IAE) regions, with an effective charge transfer of approximately $-1.645e$, $-1.477e$, and $-1.083e$ per interstitial basin in $α$-Mn, $β$-Mn, and $hex$-Mn, respectively. The electride character is further supported by the electronic density of states, where the IAE-associated states exhibit finite contributions near the Fermi level ($E_F$) and coexist with Mn-derived states, demonstrating their direct participation in the low-energy electronic structure. The combined electron localization function (ELF), effective charge transfer, and electron population due to IAE at $E_F$ therefore provide consistent evidence for interstitial anionic electrons in elemental Mn. To the best of our knowledge, this work provides the first systematic identification of spin-selective electride character in elemental Mn at ambient pressure, highlighting the possibility of exploiting its interstitial-electron states for unconventional electronic and magnetic functionalities.

cond-mat.mtrl-sci↗

arXiv2024

Confinement of quasi-atomic structures in Ti$_2$N and Ti$_3$N$_2$ MXene Electrides

Metal carbides, nitrides, or carbonitrides of early transition metals, better known as MXenes, possess notable structural, electrical, and magnetic properties. Analyzing electronic structures by calculating structural stability, band structure, density of states, Bader charge transfer, and work functions utilizing first principle calculations, we revealed that titanium nitride Mxenes, namely Ti$_2$N and Ti$_3$N$_2$, have excess anionic electrons in their pseudo-atomic structure inside the crystal lattice, making them MXene electrides. Bulk Ti$_3$N$_2$ has competing antiferromagnetic (AFM) and ferromagnetic(FM) configurations with slightly more stable AFM configurations, while the Ti$_2$N MXene is nonmagnetic. Although Ti$_3$N$_2$ favors AFM configurations with hexagonal crystal systems having $6/mmm$ point group symmetry, Ti$_3$N$_2$ does not support altermagnetism. The monolayer of the Ti$_3$N$_2$ MXene is a ferromagnetic electride. These unique properties of having non-nuclear interstitial anionic electrons in the electronic structure of titanium nitride MXene have not yet been reported in the literature. Density functional theory calculations show TiN is neither an electride, MXene, or magnetic.

cond-mat.mtrl-sci↗

arXiv2024

Topological Fermi-arc surface state covered by floating electrons on a two-dimensional electride

Two-dimensional electrides can acquire topologically non-trivial phases due to intriguing interplay between the cationic atomic layers and anionic electron layers. However, experimental evidence of topological surface states has yet to be verified. Here, via angle-resolved photoemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM), we probe the magnetic Weyl states of the ferromagnetic electride $[Gd_{2}$C]^{2+}\cdot2e^{-}$. In particular, the presence of Weyl cones and Fermi-arc states is demonstrated through photon energy-dependent ARPES measurements, agreeing with theoretical band structure calculations. Notably, the STM measurements reveal that the Fermi-arc states exist underneath a floating quantum electron liquid on the top Gd layer, forming double-stacked surface states in a heterostructure. Our work thus not only unveils the non-trivial topology of the $[Gd_{2}$C]^{2+}\cdot2e^{-}$ electride but also realizes a surface heterostructure that can host phenomena distinct from the bulk.

cond-mat.mtrl-sci↗

arXiv2023

First-principles prediction of structural, magnetic properties of Cr-substituted strontium hexaferrite, and its site preference

To investigate the structural and magnetic properties of Cr-doped M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) with x = (0.0, 0.5, 1.0), we perform first-principles total-energy calculations relied on density functional theory. Based on the calculation of the substitution energy of Cr in strontium hexaferrite and formation probability analysis, we conclude that the doped Cr atoms prefer to occupy the 2a, 12k, and 4f$_{2}$ sites which is in good agreement with the experimental findings. Due to Cr$^{3+}$ ion moment, 3 {$μ_B$}, smaller than that of Fe$^{3+}$ ion, 5 {$μ_B$}, saturation magnetization (M$_{s}$) reduce rapidly as the concentration of Cr increases in strontium hexaferrite. The magnetic anisotropic field $\left(H_{a}\right)$ rises with an increasing fraction of Cr despite a significant reduction of magnetization and a slight increase of magnetocrystalline anisotropy $\left(K_{1}\right)$.The cause for the rise in magnetic anisotropy field $\left(H_{a}\right)$ with an increasing fraction of Cr is further emphasized by our formation probability study. Cr$^{3+}$ ions prefer to occupy the 2a sites at lower temperatures, but as the temperature rises, it is more likely that they will occupy the 12k site. Cr$^{3+}$ ions are more likely to occupy the 12k site than the 2a site at a specific annealing temperature (>700°C).

cond-mat.mtrl-sci↗

arXiv2022

Quantum electron liquid and its possible phase transition

Purely quantum electron systems exhibit intriguing correlated electronic phases by virtue of quantum fluctuations in addition to electron-electron interactions. To realize such quantum electron systems, a key ingredient is dense electrons decoupled from other degrees of freedom. Here, we report the discovery of a pure quantum electron liquid, which spreads up to ~ 3 Å in the vacuum on the surface of electride crystal. An extremely high electron density and its weak hybridisation with buried atomic orbitals evidence the quantum and pure nature of electrons, that exhibit a polarized liquid phase as demonstrated by our spin-dependent measurement. Further, upon enhancing the electron correlation strength, the dynamics of quantum electrons changes to that of non-Fermi liquid along with an anomalous band deformation, suggestive of a transition to a hexatic liquid crystal phase. Our findings cultivate the frontier of quantum electron systems, and serve as a platform for exploring correlated electronic phases in a pure fashion.

cond-mat.str-el↗

arXiv2022

First principle investigations of the structural, electronic, and phase stability in 2D layered ZnSb

Recently, the two dimensional (2D) materials have become a potential candidates for various technological applications in spintronics and optoelectronics. In the present study, the structural, electronic, and phase stability of 2D layered ZnSb compounds of four different phases viz. wurzite(w), tetragonal (t), hexagonal (h), and orthorhombic (o) have been tuned using the first principle calculations based on density functional theory (DFT). We invoked the Perdew-Burke-Ernzerhof (PBE) functional and the projected augmented wave (PAW) method during all the calculations. Based on our numerical results, we predicted the novel tetragonal phase as stable phase of ZnSb next to existing orthorhombic structure. We reported the pressure induced phase transition between orthorhombic to tetragonal phase at 12.48 GPa/atom. The projected density of states indicates the strong p-d hybridization between Sb-5p and Zn-3d states confirming the nature of strong covalent bonding between them. The electronic band structures suggest that t-ZnSb, w-ZnSb, and h-ZnSb are metallic in nature whereas o-ZnSb is semiconducting with narrow band gap of 0.03 eV using PBE. We predicted the possibility of extracting the two dimensional (2D) monolayer sheet in t-ZnSb and o-ZnSb according to the exfoliation energy criterion. In addition, the 2D monolayer (ML) of o-ZnSb has been predicted to be dynamically stable but that of t-ZnSb is not stable as manifested in phonon dispersion bands. Surprisingly, the semiconducting band gap nature of o-ZnSb changes from indirect and narrow to direct and sizable while going from 3D bulk to 2D ML structure. Further, we estimated the value of work functions for the surfaces of t-ZnSb and o-ZnSb as 4.61 eV and 4.04 eV respectively. Such materials can find the niche applications in next generation electronic devices utilizing 2D hetero-structures.

physics.comp-ph↗

arXiv2018

Correlation between site preference and magnetic properties of Zn-Sn-substituted strontium hexaferrite

The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) have been investigated using first-principles total energy calculations based on density functional theory. The site occupancy of substituted atoms were estimated by calculating the substitution energies of different configurations. The distribution of different configurations during the annealing process at high temperature was determined using the formation probabilities of configurations to calculate magnetic properties of substituted strontium hexaferrite. We found that the magnetization and magnetocrystalline anisotropy are closely related to the distributions of Zn-Sn ions on the five Fe sites. Our calculation show that in SrFe$_{11.5}$Zn$_{0.5}$O$_{19}$, Zn atoms prefer to occupy $4f_1$, $12k$, and $2a$ sites with occupation probability of 78%, 19% and 3%, respectively, while in SrFe$_{11.5}$SnO$_{19}$, Sn atoms occupy the $12k$ and $4f_2$ sites with occupation probability of 54% and 46%, respectively. We also found that in SrFe$_{11}$Zn$_{0.5}$Sn$_{0.5}$O$_{19}$, (Zn,Sn) atom pairs prefer to occupy the ($4f_1$, $4f_2$), ($4f_1$, $12k$) and ($12k$, $12k$) sites with occupation probability of 82%, 8% and 6%, respectively. Our calculation shows that the increase of magnetization and the reduction of magnetic anisotropy in Zn-Sn substituted M-type strontium hexaferrite as observed experimentally is due to the occupation of (Zn,Sn) pairs at the ($4f_1$, $4f_2$) sites.

cond-mat.mtrl-sci↗