Tutul Biswas

Zitterbewegung of electrons in quantum wells and dots in the 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 (SOIs). We obtain a general expression of the time-evolution of the position vector and current of the electron in a semiconductor QW. 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 QW does not vanish when the strengths of the Rashba and Dresselhaus SOIs are equal. The in-plane magnetic field helps to sustain the ZB in QWs even at a low value of k(0)d (where d is the width of the Gaussian wavepacket and k(0) is the initial wavevector). The trembling motion of an electron in a semiconductor QW with high Landé g-factor (e.g. InSb) is sustained over a long time, even at a low value of k(0)d. Further, we study the ZB of an electron in QDs 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 QDs 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.

Wave packet dynamics and zitterbewegung of heavy holes in a quantizing magnetic field

In this work, we study wave packet dynamics and zitterbewegung, an oscillatory quantum motion, of heavy holes in III-V semiconductor quantum wells in presence of a quantizing magnetic field. It is revealed that a Gaussian wave-packet describing a heavy hole diffuses asymmetrically along the circular orbit while performing cyclotron motion. The wave packet splits into two peaks with unequal amplitudes after a certain time depending on spin-orbit coupling constant. This unequal splitting of the wave packet is attributed to the cubic Rashba interaction for heavy holes. The difference in the peak amplitudes disappears with time. At a certain time, the two peaks diffuse almost along the entire cyclotron orbit. Then tail and head of the diffused wave packet interfere and as a result a completely randomized pattern of the wave packet is observed. The diffusion rate of the wave packet increases with increase of the spin-orbit interaction strength. Also strong spin-orbit coupling expedite the splitting and the ran...

Zitterbewegung of a heavy hole in presence of spin-orbit interactions

We study the zitterbewegung of a heavy hole in presence of both cubic Rashba and cubic Dresselhaus spin-orbit interactions. On contrary to the electronic case, zitterbewegung does not vanish for equal strength of Rashba and Dresselhaus spin-orbit interaction. This non-vanishing of zitterbewegung is associated with the Berry phase. Due to the presence of the spin-orbit coupling the spin associated with the heavy hole precesses about an effective magnetic field. This spin precession produces a transverse spin-orbit force which also generates an electric voltage associated with zitterbewegung. We have estimated the magnitude of this voltage for a possible experimental detection of zitterbewegung.

Acoustic phonon-limited resistivity of spin?orbit coupled two-dimensional electron gas: the deformation potential and piezoelectric scattering

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

Wave packet dynamics in monolayer MoS 2 with and without a magnetic field

Abstract We study the dynamics of electrons in monolayer molybdenum disulfide (MoS2), in the absence as well as presence of a transverse magnetic field. Considering the initial electronic wave function to be a minimum uncertainty Gaussian wave packet, we calculate the time dependent expectation value of position and velocity operators analytically. 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 based on general arguments. Our results may also be useful, for the interpretation of experiments with trapped ions, as in [R. Gerritsma, G. Kirchmair, F. Zahringer, E. Solano, R. Blatt, C.F. Roos, Nature 463, 68 (2010)], which performs a proof-of-principle quantum simulation of the one-dimensional Dirac equation.

Magnetotransport properties of 2D fermionic systems with k -cubic Rashba spin-orbit interaction

The spin-orbit interaction in heavy hole gas formed at p-doped semiconductor heterojunctions and electron gas at SrTiO3 surfaces is cubic in momentum. Here we report magnetotransport properties of k-cubic Rashba spin-orbit coupled 2D fermionic systems. We study longitudinal and Hall components of the resistivity tensor analytically as well as numerically. The longitudinal resistivity shows a beating pattern due to different Shubnikov-de Haas (SdH) oscillation frequencies f ± for spin-up and spin-down fermions. We propose empirical forms of f ± as exact expressions are not available, which are being used to find locations of the beating nodes. The beating nodes and the number of oscillations between any two successive nodes obtained from exact numerical results are in excellent agreement with those calculated from the proposed empirical formula. In the Hall resistivity, an additional Hall plateau appears between the two conventional ones as the spin-orbit coupling constant increases. The width of this additional plateau increases with spin-orbit coupling constant.

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

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

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

We study the phonon-drag contribution to the thermoelectric power in a quasi-two-dimensional electron system confined in GaAs/AlGaAs heterostructure in the 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.

Quantum information entropies of ultracold 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 containing N atoms confined in a D( ≤ 3)-dimensional harmonic trap has a universal form as

Phonon-drag magnetoquantum oscillations in graphene

S_\mathrm{t}^{(D)} = N(a D - b \ln N)