arXiv subjects

Barun Ghosh

Publications and source records attributed to Barun Ghosh.

43 records · Page 3Linked to original sources

arXiv2018

Topological Hourglass Dirac Semimetal in the Nonpolar Phase of Ag$_2$BiO$_3$

Materials with tunable charge and lattice degrees of freedom provide excellent platforms for investigating multiple phases that can be controlled via external stimuli. We show how the charge-ordered ferroelectric oxide Ag$_2$BiO$_3$, which has been realized experimentally, presents a unique exemplar of a metal-insulator transition under an external electric field. Our first-principles calculations, combined with a symmetry analysis, reveal the presence of a nearly ideal hourglass-Dirac-semimetal state in the nonpolar structure of Ag$_2$BiO$_3$. The low-energy band structure consists of two hourglasslike nodal lines located on two mutually orthogonal glide-mirror planes in the absence of spin-orbit coupling (SOC) effects. These lines cross at a common point and form an interlinked chainlike structure, which extends beyond the first Brillouin zone. Inclusion of the SOC opens a small gap in the nodal lines and results in two symmetry-enforced hourglasslike Dirac points on the $\tilde{\mathcal{C}}_{2y}$ screw rotation axis. Our results indicate that Ag$_2$BiO$_3$ will provide an ideal platform for exploring the ferroelectric-semiconductor to Dirac-semimetal transition by the application of an external electric field.

cond-mat.mes-hall↗

arXiv2018

Broadband excitation spectrum of bulk crystals and thin layers of PtTe$_2$

We explore the broadband excitation spectrum of bulk PtTe$_2$ using electron energy loss spectroscopy and density functional theory. In addition to infrared modes related to intraband 3D Dirac plasmon and interband transitions between the 3D Dirac bands, we observe modes at 3.9, 7.5 and 19.0 eV in the ultraviolet region. The comparison of the excitation spectrum with the calculated orbital-resolved density of states allows us to ascribe spectral features to transitions between specific electronic states. Additionally, we study the thickness dependence of the high-energy plasmon in the PtTe2 thin films. We show that, unlike graphene, the high-energy plasmon in PtTe2 thin film gets red-shifted by 2.5 eV with increasing thickness.

cond-mat.mes-hall↗

arXiv2017

Anisotropic plasmons, excitons and electron energy loss spectroscopy of phosphorene

In this article, we explore the anisotropic electron energy loss spectrum (EELS) in monolayer phosphorene based on ab-initio time dependent density functional theory calculations. Similar to black phosphorous, the EELS of undoped monolayer phosphorene is characterized by anisotropic excitonic peaks for energies in vicinity of the bandgap, and by interband plasmon peaks for higher energies. On doping, an additional intraband plasmon peak also appears for energies within the bandgap. Similar to other two dimensional systems, the intraband plasmon peak disperses as $ω_{\rm pl} \propto \sqrt{q}$ in both the zigzag and armchair directions in the long wavelength limit, and deviates for larger wavevectors. The anisotropy of the long wavelength plasmon intraband dispersion is found to be inversely proportional to the square root of the ratio of the effective masses: $ω_{\rm pl}(q \hat{y})/ω_{\rm pl}(q \hat{x}) = \sqrt{m_x/m_y}$.

cond-mat.mes-hall↗

arXiv2016

Electric-field tunable Dirac semimetal state in phosphorene thin films

We study the electric-field tunable electronic properties of phosphorene thin films, using the framework of density functional theory. We show that phosphorene thin films offer a versatile material platform to study two dimensional Dirac fermions on application of a transverse electric field. Increasing the strength of the transverse electric field beyond a certain critical value in phosphorene leads to the formation of two symmetry protected gapless Dirac fermions states with anisotropic energy dispersion. The spin-orbit coupling splits each of these Dirac state into two spin- polarized Dirac cones which are also protected by non-symmorphic crystal symmetries. Our study shows that the position as well as the carrier velocity of the spin polarized Dirac cone states can be controlled by the strength of the external electric field.

cond-mat.mes-hall↗

arXiv2016

Electrical and optical conductivities of hole gas in $p$-doped bulk III-V semiconductors

We study electrical and optical conductivities of hole gas in $p$-doped bulk III-V semiconductors described by the Luttinger Hamiltonian. We provide exact analytical expressions of the Drude conductivity, inverse relaxation time for various impurity potentials, Drude weight and optical conductivity in terms of the Luttinger parameters $γ_1 $ and $γ_2$. The back scattering is completely suppressed as a result of the helicity conservation of the heavy and light hole states. We find that the inverse relaxation time of heavy holes is much less than that of the light holes for Coulomb-type and Gaussian-type impurity potentials and vice-versa for short-range impurity potentials. The Drude conductivity increases non-linearly with the increase of the hole density. The exponent of the density dependence of the conductivity is obtained in Thomas-Fermi limit. The Drude weight varies linearly with the density even in presence of the spin-orbit coupling. The finite-frequency optical conductivity goes as $\sqrtω$ and its amplitude strongly depends on the Luttinger parameters. The Luttinger parameters can be extracted from the optical conductivity measurement.

cond-mat.mes-hall↗

arXiv2016

New ground states of fluorinated and oxidized phosphorene: structural and electronic properties

We systematically explore chemical functionalization of monolayer black phosphorene via chemisorption of oxygen and fluorine atoms. Using the cluster expansion technique, with vary- ing concentration of the adsorbate, we determine the ground states considering both single- as well as double- side chemisorption, which have novel chemical and electronic properties. The nature of the bandgap depends on the concentration of the adsorbate: for fluorination the direct bandgap first decreases, and then increases while becoming indirect, with increasing fluorination, while for oxidation the bandgap first increases and then decreases, while mostly maintaining its direct nature. Further we find that the unique anisotropic free-carrier effective mass for both the electrons and holes, can be changed and even rotated by 90 degrees, with controlled chemisorption, which can be useful for exploring unusual quantum Hall effect, and novel electronic devices based on phosphorene.

cond-mat.mtrl-sci↗

arXiv2015

Electric field induced gap modification in ultrathin blue phosphorous

We investigate the possibility of band structure engineering in the recently predicted 2D layered form of blue phosphorus via an electric field (E$_z$) applied perpendicular to the layer(s). Using density functional theory, we study the effect of a transverse electric field in monolayer, as well as three differently stacked bilayer structures of blue phosphorus. We find that, for E$_z > 0.2$ V/Å the direct energy gap at the $Γ$ point, which is much larger than the default indirect band gap of mono- and bilayer blue phosphorus, decreases linearly with the increasing electric field; becomes comparable to the default indirect band gap at E$_z \approx 0.45 (0.35)$ V/Å for monolayer (bilayers) and decreases further until the semiconductor to metal transition of 2D blue phosphorus takes place at E$_z\approx 0.7 (0.5)$ V/Å for monolayer (bilayers). Calculated values of the electron and hole effective masses along various high symmetry directions in the reciprocal lattice suggests that the mobility of charge carriers is also influenced by the applied electric field.

cond-mat.mes-hall↗