arXiv subjects

Sanchari Bhattacharya

Publications and source records attributed to Sanchari Bhattacharya.

4 recordsLinked to original sources

arXiv2023

Rashba splitting in polar-nonpolar sandwich heterostructure : A DFT Study

In this study, we employ density functional theory (DFT) based first-principles calculations to investigate the spin-orbit effects in the electronic structure of a polar-nonpolar sandwich heterostructure namely LAO$_{2.5}$/STO$_{5.5}$/LAO$_{2.5}$. Our focus on the Ti-3d bands reveals an inverted ordering of the STO-$\rm t_{2g}$ orbital near the n-type interface, consistent with earlier experimental work. In contrast, toward the p-type interface, the orbital ordering aligns with the natural ordering of STO orbitals, influenced by crystal field splitting. Interestingly, we have found a strong inter-orbital coupling between $t_{2g}$ and $e_g$ orbital, which has not been reported earlier in $\rm SrTiO_3$ based 2D system. Additionally, our observations highlight that the cubic Rashba splitting in this system surpasses the linear Rashba splitting, contrary to experimental findings. This comprehensive analysis contributes to a refined understanding of the role of orbital mixing in Rashba splitting in the sandwich oxide heterostructures.

cond-mat.mtrl-sci↗

arXiv2023

Evidence of linear and cubic Rashba effect in non-magnetic heterostructure

The LaAlO3/KTaO3 system serves as a prototype to study the electronic properties that emerge as a result of spin-orbit coupling. In this article, we have used first-principles calculations to systematically study two types of defect-free (0 0 1) interfaces, which are termed as Type-I and Type-II. While the Type-I heterostructure produces a two-dimensional electron gas, the Type-II heterostructure hosts an oxygen-rich two-dimensional hole gas at the interface. Furthermore, in the presence of intrinsic spin-orbit coupling, we have found evidence of both cubic and linear Rashba interactions in the conduction bands of the Type-I heterostructure. On the contrary, there is spin-splitting of both the valence and the conduction bands in the Type-II interface, which are found to be only linear Rashba type. Interestingly, the Type-II interface also harbours a potential photocurrent transition path, making it an excellent platform to study the circularly polarized photogalvanic effect.

cond-mat.mtrl-sci↗

arXiv2021

Signature of half-metallicity in $\text{BiFeO}_\text{3}$

$\text{BiFeO}_\text{3}$ has drawn a great attention over last several decades due to its promising multiferroic character. In the ground state the bulk $\text{BiFeO}_\text{3}$ is found to be in the rhombohedral phase. However, it has been possible to stabilize $\text{BiFeO}_\text{3}$ with tetragonal structure. The importance of tetragonal phase is due to its much larger value of the electric polarization and the possible stabilization of ferromagnetism as in the rhombohedral phase. Furthermore, the tetragonal structure of $\text{BiFeO}_\text{3}$ has been reported with different $c/a$ ratio, opening up the possibility of a much richer set of electronic phases. In this work, we have used density functional theory based first-principle method to study the ferromagnetic phase of the tetragonal $\text{BiFeO}_\text{3}$ structure as a function of the $c/a$ ratio. We have found that as the $c/a$ ratio decreases from $1.264$ to $1.016$, the tetragonal $\text{BiFeO}_\text{3}$ evolve from a ferromagnetic semiconductor to a ferromagnetic metal, while passing through a \emph{half-metallic} phase. This evolution of the electronic properties becomes even more interesting when viewed with respect to the volume of each structure. The most stable half-metallic phase initially counter-intuitively evolve to the magnetic-semiconducting phase with a reduction in the volume, and after further reduction in the volume it finally becomes a metal. So far, this type of metal to insulator transition on compression was known to exist only in alkali metals, especially in Lithium, in heavy alkaline earth metals, and in some binary compound.

cond-mat.mtrl-sci↗

arXiv2016

Subdiffusion, Anomalous Diffusion and Propagation of a Particle Moving in Random and Periodic Media

We investigate the motion of a single particle moving on a two-dimensional square lattice whose sites are occupied by right and left rotators. These left and right rotators deterministically rotate the particle's velocity to the right or left, respectively and \emph{flip} orientation from right to left or from left to right after scattering the particle. We study three types of configurations of left and right rotators, which we think of as types of media, through with the particle moves. These are completely random (CR), random periodic (RP), and completely periodic (CP) configurations. For CR configurations the particle's dynamics depends on the ratio $r$ of right to left scatterers in the following way. For small $r\simeq0$, when the configuration is nearly homogeneous, the particle subdiffuses with an exponent of 2/3, similar to the diffusion of a macromolecule in a crowded environment. Also, the particle's trajectory has a fractal dimension of $d_f\simeq4/3$, comparable to that of a self-avoiding walk. As the ratio increases to $r\simeq 1$, the particle's dynamics transitions from subdiffusion to anomalous diffusion with a fractal dimension of $d_f\simeq 7/4$, similar to that of a percolating cluster in 2-d. In RP configurations, which are more structured than CR configurations but also randomly generated, we find that the particle has the same statistic as in the CR case. In contrast, CP configurations, which are highly structured, typically will cause the particle to go through a transient stage of subdiffusion, which then abruptly changes to propagation. Interestingly, the subdiffusive stage has an exponent of approximately 2/3 and a fractal dimension of $d_f\simeq4/3$, similar to the case of CR and RP configurations for small $r$.

cond-mat.stat-mech↗