Pradip Kumar Jha

Thermodynamic behaviour of Rashba quantum dot in the presence of magnetic field

The thermodynamic properties of an InSb quantum dot have been investigated in the presence of Rashba spin–orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy, magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2k B with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin–orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.

Nonlinear interband and intersubband transitions in quantum dots for multiphoton photodetectors

Accurate nonperturbative Floquet theory is used to study nonlinear multiphoton transitions in quantum dot involving interband and intersubband states. The interband transitions generate electron-hole pairs, which in turn give rise to photocurrent useful for making multiphoton photodetector. We find the direct role of multiphoton absorption processes over the single photon absorption in enhancing the sensitivity of the photodetector for photon energy equal to or less than the half of the bandgap energy.

Optical response of a two dimensional quantum ring in presence of Rashba spin orbit coupling

The influence of Rashba spin orbit interaction on the optical properties of two dimensional mesoscopic ring has been investigated in the presence of uniform perpendicular magnetic field. The Schrodinger equation for the Rashba coupled system is solved by effective mass approximation and diagonalization technique. Using the calculated energies and eigenfunctions, the laser field induced change in refractive index and optical absorption have been studied under the density matrix formalism. It has been found that Rashba spin orbit interaction removes the intersection of energy levels; however, avoided crossings are observed at finite magnetic field. At sufficient high values of Rashba coupling or laser intensity, the optical response of quantum ring is found to be dominated by third order nonlinear term. Also, Rashba interaction shifts the value of magnetic field that is needed to suppress the absorption drastically and to pass the incident light unattenuated. The results reveal that the geometry of the ring...

Study of half-metallicity in BiMnxFe1-xO3

Spin polarized calculations are performed to study the structural and electronic properties of Mn doped BiFeO3 (BMFO) using simplified local spin density approximation (LSDA) functional under density functional theory (DFT). The B-site doping concentration of Mn in BMFO considered to be 16.7 % (BiMn0.167Fe0.833O3). Density of states calculations are carried out for both ferromagnetic (FM) and anti-ferromagnetic (AFM) order in BMFO. The results predict that BMFO is a half metal for both FM and AFM BMFO with magnetization of 29.0000 µB/cell and 1.0000 µB/cell respectively. The ground state of BMFO is found to be antiferromagnetic and demonstrates BMFO to be a potential candidate for spintronic applications.

Symmetries of the renormalization group equations

The invariance of the renormalization group equation under the action of the prolonged Lie field is examined and it is shown that the system exhibits infinite dimensional symmetry. From the characteristics, detailed solutions of the renormalization group equation is derived. As an illustration, the method is applied to QED and QCD.

A theoretical and experimental formalism of electronic structure of BFO:Cr thin films and modulation of their electrical properties upon visible light illumination

BiFeO3 (BFO) and BiFe1-xCrxO3 (BFCO) (x = 0, 0.01, 0.02, 0.03) thin films have been fabricated using chemical solution deposition technique. The bandgap of BFO and BFCO thin films is found to be lying in the visible region making these films suitable candidates for potential solar energy harvesting applications. Density functional theory based calculations have also been performed to study the effect of B-site (Cr) doping on the electronic properties of BFO and BFCO. The BiFe1-xCrxO3 (x = 0.02) thin films exhibited well saturated PE hysteresis loops with a maximum remanent and saturation polarization of about 43 μC/cm2 and 64 μC/cm2, respectively. In contrast to pure BFO, a high value of short circuit current density (Jsc) of magnitude 766.60 μA/cm2 along with the open circuit voltage (Voc) of 106 mV was obtained for BiFe0.98Cr0.02O3 thin film structure under illumination with a laser of wavelength 470 nm and intensity 20 mW/cm2. The Au/BiFe0.98Cr0.02O3/ITO/glass heterostructure displays a remarkably enhanced value of Ion/Ioff ratio (8.4 × 104). The observed results clearly highlight the potential of Cr doped BFO thin film structure for the development of cost effective light-driven devices.

The Luttinger liquid in superlattice structures: atomic gases, quantum dots and the classical Ising chain

We study the physical properties of a Luttinger liquid in a superlattice that is characterized by alternating two tunneling parameters. Using the bosonization approach, we describe the corresponding Hubbard model by the equivalent Tomonaga–Luttinger model. We analyze the spin–charge separation and transport properties of the superlattice system. We suggest that cold Fermi gases trapped in a bichromatic optical lattice and coupled quantum dots offer the opportunity to measure these effects in a convenient manner. We also study the classical Ising chain with two tunneling parameters. We find that the classical two-point correlator decreases as the difference between the two tunneling parameters increases.