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Tarun Kanti Ghosh

Publications and source records attributed to Tarun Kanti Ghosh.

At least 55 records · Page 3Linked to original sources
arXiv2014

Wave packet dynamics in monolayer MoS$_2$ with and without a magnetic field

We study the dynamics of electrons in monolayer Molybdenum Disulfide (MoS$_2$), in the absence as well as presence of a transverse magnetic field. Considering the initial electronic wave function to be a Gaussian wave packet, we calculate the time dependent expectation value of position and velocity operators. In the absence of the magnetic field, the time dependent average values of position and velocity show damped oscillations dependent on the width of the wave packet. In the presence of a transverse magnetic field, the wave packet amplitude shows oscillatory behaviour over short timescales associated with classical cyclotron orbit, followed by the phenomena of spontaneous collapse and revival over larger timescales. We relate the timescales of these effects and our results can be useful for the interpretation of experiments with trapped ions.

cond-mat.mes-hall↗
arXiv2014

Beating pattern in quantum magnetotransport coefficients of spin-orbit coupled Dirac fermions in gated silicene

We report theoretical study of magnetotransport coefficients of spin-orbit coupled gated silicene in presence and absence of spatial periodic modulation. The combined effect of spin-orbit coupling and perpendicular electric field manifests through formation of regular beating pattern in Weiss and SdH oscillations. Analytical results, in addition to the numerical results, of the beating pattern formation are provided. The analytical results yield a beating condition which will be useful to determine the spin-orbit coupling constant by simply counting the number of oscillation between any two successive nodes. Moreover, the numerical results of modulation effect on collisional and Hall conductivities are presented.

cond-mat.mes-hall↗
arXiv2014

Thermoelectric properties of an ultra-thin topological insulator

Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In absence of magnetic field, thermopower increases and thermal conductivity decreases with increase of the hybridization energy. In presence of magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and phase factor is governed by the product of the Lande g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results of the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, whose frequency depends on the Lande g-factor.

cond-mat.mes-hall↗
arXiv2013

Phonon-drag magnetothermopower in Rashba spin-split two-dimensional electron systems

We study phonon-drag contribution to the thermoelectric power in a quasi-two-dimensional electron system confined in GaAs/AlGaAs heterostructure in presence of both Rashba spin-orbit interaction and perpendicular magnetic field at very low temperature. It is observed that the peaks in the phonon-drag thermopower split into two when the Rashba spin-orbit coupling constant is strong. This splitting is a direct consequence of the Rashba spin-orbit interaction. We show the dependence of phonon-drag thermopower on both magnetic field and temperature numerically. A power-law dependence of phonon-drag magnetothermopower on the temperature in the Bloch-Gruneisen regime is found. We also extract the exponent of the temperature dependence of phonon-drag thermopower for different parameters like electron density, magnetic field, and the spin-orbit coupling constant.

cond-mat.mes-hall↗
arXiv2013

Phonon-drag thermopower and hot-electron energy-loss rate in a Rashba spin-orbit coupled two-dimensional electron system

We theoretically study phonon-drag contribution to the thermoelectric power and hot-electron energy-loss rate in a Rashba spin-orbit coupled two-dimensional electron system (2DES) in the Bloch-Gruneisen (BG) regime. We assume that electrons interact with longitudinal acoustic phonons through deformation potential and with both longitudinal and transverse acoustic phonons through piezoelectric potential. Effect of the Rashba spin-orbit interaction on magnitude and temperature dependence of the phonon-drag thermoelectric power and hot-electron energy-loss rate are discussed. We numerically extract the exponent of temperature dependence of the phonon-drag thermopower and the energy-loss rate. We find the exponents are strongly suppressed due to the presence of the Rashba spin-orbit coupling.

cond-mat.mes-hall↗
arXiv2013

In-plane electric field effect on a spin-orbit coupled two-dimensional electron system in presence of magnetic field

The effect of in-plane electric field on Landau level spacing, spin splitting energy, average spin polarization and average spin current in the bulk as well as at the edges of a two-dimensional electron system with Rashba spin-orbit coupling are presented here. The spin splitting energy for a particular magnetic field is found to be reduced by the external in-plane electric field. Unlike the case of a two-dimensional electron system without Rashba spin-orbit interaction, here the Landau level spacing is electric field dependent. This dependency becomes stronger at the edges in comparison to the bulk. The average spin polarization vector rotates anti-clockwise with the increase of electric field. The average spin current also gets influenced significantly by the application of the in-plane electric field.

cond-mat.mes-hall↗
arXiv2012

Acoustic phonon-limited resistivity in spin-orbit coupled 2DEG: Deformation potential and piezoelectric scattering

We study the interaction between electron and acoustic phonon in a Rashba spin-orbit coupled two dimensional electron gas using Boltzmann transport theory. Both deformation potential and piezoelectric scattering mechanisms are considered in the Bloch-Gruneisen (BG) as well as in the equipartition (EP) regimes. Effect of the Rashba spin-orbit interaction on the temperature dependence of resistivity in the BG and EP regimes has been discussed. We find effective exponent of the temperature dependence of the resistivity in the BG regime decreases due to spin-orbit coupling.

cond-mat.mes-hall↗
arXiv2012

Thermoelectric probe for Rashba spin-orbit interaction strength in a two dimensional electron gas

Thermoelectric coefficients of a two dimensional electron gas with the Rashba spin-orbit interaction are presented here. In absence of magnetic field, thermoelectric coefficients are enhanced due to the Rashba spin-orbit interaction. In presence of magnetic field, the thermoelectric coefficients of spin-up and spin-down electrons oscillate with different frequency and produces beating patterns in the components of the total thermoelectric power and the total thermal conductivity. We also provide analytical expressions of the thermoelectric coefficients to explain the beating pattern formation. We obtain a simple relation which determines the Rashba SOI strength if the magnetic fields corresponding to any two successive beat nodes are known from the experiment.

cond-mat.mes-hall↗
arXiv2012

Magnetotransport properties of a magnetically modulated two-dimensional electron gas with the spin-orbit interaction

We study the electrical transport properties of a two-dimensional electron gas with the Rashba spin-orbit interaction in presence of a constant perpendicular magnetic field $(B_0 \hat z)$ which is weakly modulated by ${\bf B_1} = B_1 \cos (q x) \hat z$, where $B_1 \ll B_0 $ and $q = 2 π/a $ with $a$ is the modulation period. We obtain the analytical expressions of the diffusive conductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and produce beating patterns in the amplitude of the Weiss and Shubnikov-de Haas oscillations. We show that the Rashba strength can be determined by analyzing the beating pattern in the Weiss oscillation. We find a simple equation which determines the Rashba spin-orbit interaction strength if the number of Weiss oscillations between any two successive nodes is known from the experiment. We compare our results with the electrically modulated 2DEG with the Rashba interaction. For completeness, we also study the beating pattern formation in the collisional and the Hall conductivities.

cond-mat.mes-hall↗
arXiv2012

Zitterbewegung of electrons in quantum wells and dots in presence of an in-plane magnetic field

We study the effect of an in-plane magnetic field on the zitterbewegung (ZB) of electrons in a semiconductor quantum well (QW) and in a quantum dot (QD) with the Rashba and Dresselhaus spin-orbit interactions. We obtain a general expression of the time-evolution of the position vector and current of the electron in a semiconductor quantum well. The amplitude of the oscillatory motion is directly related to the Berry connection in momentum space. We find that in presence of the magnetic field the ZB in a quantum well does not vanish when the strengths of the Rashba and Dresselhaus spin-orbit interactions are equal. The in-plane magnetic field helps to sustain the ZB in quantum wells even at low value of $k_0 d$ (where $d$ is the width of the Gaussian wavepacket and $k_0$ is the initial wave vector). The trembling motion of an electron in a semiconductor quantum well with high Lande g-factor (e.g. InSb) sustains over a long time, even at low value of $k_0 d$. Further, we study the ZB of an electron in quantum dots within the two sub-band model numerically. The trembling motion persists in time even when the magnetic field is absent as well as when the strengths of the SOI are equal. The ZB in quantum dots is due to the superposition of oscillatory motions corresponding to all possible differences of the energy eigenvalues of the system. This is an another example of multi-frequency ZB phenomenon.

cond-mat.mes-hall↗
arXiv2011

Zero-field spin splitting in a two-dimensional electron gas with the spin-orbit interaction revisited

We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction (SOI) in presence of a perpendicular magnetic field. We derive analytical expressions of the density of states (DOS) of a 2DEG with the Rashba SOI in presence of magnetic field by using the Green's function technique. The DOS allows us to obtain the analytical expressions of the magnetoconductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and gives rise to the beating patterns in the amplitude of the Shubnikov de Hass (SdH) oscillations. We find a simple equation which determines the zero-field spin splitting energy if the magnetic field corresponding to any beat node is known from the experiment. Our analytical results reproduce well the experimentally observed non-periodic beating patterns, number of oscillations between two successive nodes and the measured zero-field spin splitting energy.

cond-mat.mes-hall↗
arXiv2011

Localization of Dirac-like excitations in graphene in the presence of smooth inhomogeneous magnetic fields

The present article discusses magnetic confinement of the Dirac excitations in graphene in presence of inhomogeneous magnetic fields. In the first case a magnetic field directed along the z axis whose magnitude is proportional to $1/r$ is chosen. In the next case we choose a more realistic magnetic field which does not blow up at the origin and gradually fades away from the origin. The magnetic fields chosen do not have any finite/infinite discontinuity for finite values of the radial coordinate. The novelty of the two magnetic fields is related to the equations which are used to find the excited spectra of the excitations. It turns out that the bound state solutions of the two-dimensional hydrogen atom problem are related to the spectra of graphene excitations in presence of the $1/r$ (inverse-radial) magnetic field. For the other magnetic field profile one can use the knowledge of the bound state spectrum of a two-dimensional cut-off Coulomb potential to dictate the excitation spectra of the states of graphene. The spectrum of the graphene excitations in presence of the inverse-radial magnetic field can be exactly solved while the other case cannot be. In the later case we give the localized solutions of the zero-energy states in graphene.

cond-mat.mes-hall↗
arXiv2011

Quantum information entropies of ultra-cold atomic gases in a harmonic trap

The position and momentum space information entropies of weakly interacting trapped atomic Bose-Einstein condensates and spin-polarized trapped atomic Fermi gases at absolute zero temperature are evaluated. We find that sum of the position and momentum space information entropies of these quantum systems contain $N$ atoms confined in a $D(\le 3)$-dimensional harmonic trap has a universal form as $ S_t^{(D)} = N(a D - b \ln N) $, where $a \simeq 2.332$ and $b = 2$ for interacting bosonic systems and $a \simeq 1.982$ and $b = 1$ for ideal fermionic systems. These results obey the entropic uncertainty relation given by the Beckner, Bialynicki-Birula and Myceilski.

cond-mat.quant-gas↗
arXiv2011

Thermodynamic properties of a magnetically modulated graphene

The effect of magnetic modulation on thermodynamic properties of a graphene monolayer in presence of a constant perpendicular magnetic field is reported here. One-dimensional spatial electric or magnetic modulation lifts the degeneracy of the Landau levels and converts into bands and their band width oscillates with magnetic field leading to Weiss-type oscillation in the thermodynamic properties. The effect of magnetic modulation on thermodynamic properties of a graphene sheet is studied and then compared with electrically modulated graphene and magnetically modulated conventional two-dimensional electron gas (2DEG). We observe Weiss-type and de Haas-van Alphen (dHvA) oscillations at low and high magnetic field, respectively. There is a definite phase difference in Weiss-type oscillations in thermodynamic quantities of magnetically modulated graphene in compare to electrically modulated graphene. On the other hand, the phase remains same and amplitude of the oscillation is large when compared with the magnetically modulated 2DEG. Explicit asymptotic expressions of density of states and the Helmholtz free energy are provided to understand the phase and amplitude of the Weiss-type oscillations qualitatively. We also study thermodynamic properties when both electric and magnetic modulations are present. The Weiss-type oscillations still exist when the modulations are out-of-phase.

cond-mat.mes-hall↗
arXiv2007

Dynamic structure factor of Fermi superfluid in the BEC-BCS crossover

We consider cigar shaped Fermi superfluid in the BEC-BCS crossover. Using polytropic form of equation of state, we derive low energy multibranch bosonic excitations and the corresponding density fluctuations in three different regimes along the crossover, namely weak-coupling BCS, unitarity and molecular BEC regimes. Bragg spectroscopy can be used to probe the multibranch nature of the low energy bosonic excitations by measuring dynamic structure factor. Therefore, we calculate dynamic structure factor in those three different regimes. In the Bragg spectroscopy, an actual observable is momentum imparted to the superfluid due to the Bragg potential. We also present results of the momentum imparted to the superfluid due to the Bragg pulses.

cond-mat.other↗
arXiv2007

Bragg spectroscopy of a cigar shaped Bose condensate in optical lattices

We study properties of excited states of an array of weakly coupled quasi-two-dimensional Bose condensates by using the hydrodynamic theory. We calculate multibranch Bogoliubov-Bloch spectrums and its corresponding eigenfunctions. The spectrum of the axial excited states and its eigenfunctions strongly depends on the coupling among various discrete radial modes within a given symmetry. This mode coupling is due to the presence of radial trapping potential. The multibranch nature of the Bogoliubov-Bloch spectrum and its dependence on the mode-coupling can be realized by analyzing dynamic structure factor and momentum transferred to the system in Bragg spectroscopy experiments. We also study dynamic structure factor and momentum transferred to the condensate due to the Bragg spectroscopy experiment.

cond-mat.other↗
arXiv2005

Collective modes of Fermi superfluid containing vortices along the BEC-BCS crossover

Using the coarse-grain averaged hydrodynamic approach, we calculate all low energy transverse excitation spectrum of a rotating Fermi superfluid containing vortex lattices for all regimes along the BEC-BCS crossover. In the fast rotating regime, the molecular BEC enters into the lowest Landau level, but the superfluid in the unitarity and the BCS regimes occupies many low-lying Landau levels. The difference between the breathing mode frequencies at the BEC and unitarity limit shrinks to zero as the rotation speed approaches the radial trap frequency, in contrast to the finite difference in the non-rotating systems.

cond-mat.mes-hall↗