Solid State Physics Laboratory

About: Solid State Physics Laboratory is a facility organization based out in Delhi, India. It is known for research contribution in the topics: Quantum dot & Dielectric. The organization has 1754 authors who have published 2597 publications receiving 50601 citations.

Phase separation and isotope effect in the ferromagnetic insulating state of the Pr1-xCaxMnO3 system (0.2 <x <0.33)

Abstract: The magnetic and transport properties of the ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ system were studied at the characteristic points of the phase diagram corresponding to the ferromagnetic insulating and charge-ordered antiferromagnetic states. The magnetization M and resistivity $\ensuremath{\rho}$ of the ceramic samples with $x=0.2,$ 0.25, 0.27, 0.29, 0.30, and 0.33 were measured at temperatures $T=4--300\mathrm{K}$ and applied magnetic fields H up to 7 T. It was shown that the Curie temperature ${T}_{C}$ exhibits a nonmonotonic change with x. The maximum value of ${T}_{C}$ was achieved at $x=0.25.$ The isotope substitution ${}^{16}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{O}}}^{18}\mathrm{O}$ was performed for the samples with $x=0.2,0.25,$ and 0.30. A pronounced isotope effect in ${T}_{C}$ was found. A noticeable drop in the activation energy ${E}_{a}$ below the Curie temperature and a decrease of resistivity in the magnetic field both in the ferromagnetic insulator phase and in the phase-separated region at $xg0.3$ were observed. Special attention is paid to the possible manifestations of the phase separation in the ferromagnetic insulating state.

Graphene quantum dots in perpendicular magnetic fields

Abstract: We report transport experiments on graphene quantum dots (QDs). We focus on excited state spectra in the near vicinity of the charge neutrality point and signatures of the electron-hole crossover as a function of a perpendicular magnetic field. Coulomb blockade resonances of a 50 nm wide and 80 nm long dot are visible at all gate voltages across the transport gap ranging from hole to electron transport. The magnetic field dependence of more than 40 states as a function of the back gate voltage can be interpreted in terms of the unique evolution of the diamagnetic spectrum of a graphene dot including the formation of the E = 0 Landau level, situated in the centre of the transport gap, and marking the electron-hole crossover. Around the crossover, excited states and cotunneling features are studied for varying perpendicular magnetic field. Schematic illustration of an etched graphene quantum dot with rough edges. The devices studied are still significantly larger than the presented one.

A general relation between zero-bias resistance - area product and perimeter-to-area ratio of the diodes in variable-area diode test structures

Abstract: This paper is an attempt towards presenting a general analytical relation between the inverse of zero-bias resistance - area product and the perimeter-to-area ratio of the diodes in variable-area diode array test structures currently used in HgCdTe technology Contributions from (i) surface leakage currents due to band bending at the HgCdTe surface (ie the HgCdTe - passivant interface), (ii) surface generation currents in the depletion region in the immediate proximity of the HgCdTe - passivant interface, (iii) surface leakage currents due to Zener tunnelling, (iv) leakage currents due to an imperfect HgCdTe epilayer - substrate interface and (v) bulk currents have all been taken into consideration in arriving at the relationship between the inverse of zero-bias resistance - area product and the perimeter-to-area (p/A) ratio of the diodes The derived relation predicts in general a nonlinear behaviour of the data It is shown by the detailed discussions that the general relation can be of great practical help in identifying the various possible mechanisms contributing to the surface leakage currents Use of constant perimeter and variable-area (CPVA) test structures along with the usual variable perimeter and area (VPA) test structures to interpret the linear data, and additional experiments to distinguish the surface Zener tunnelling and surface generation - recombination mechanisms have been proposed The previously reported data on variable-area test structures have been shown to fit very well with the presented model

Spin-orbit splitting and effective masses in p-type GaAs two-dimensional hole gases

Abstract: We present magnetotransport measurements performed on two-dimensional hole gases embedded in carbon doped $p$-type GaAs/AlGaAs heterostructures grown on [001] oriented substrates. A pronounced beating pattern in the Shubnikov--de Haas oscillations proves the presence of strong spin-orbit interaction in the device under study. We estimate the effective masses of spin-orbit-split subbands by measuring the temperature dependence of the Shubnikov--de Haas oscillations at different hole densities. While the lighter heavy-hole effective mass is not energy dependent, the heavier heavy-hole effective mass has a prominent energy dependence, indicating a strong spin-orbit induced nonparabolicity of the valence band. The measured effective masses show qualitative agreement with self-consistent numerical calculations.