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.

Liquid crystalline materials: physical properties and intermolecular interactions

Abstract: The physical properties and the phase behaviour of some nematic liquid crystals are discussed, with emphasis on the influence of short-range antiparallel dipole correlation that occurs in mesogenic compounds with a strong terminal dipole moment. Evidence for this effect, which stems especially from dielectric studies, is summarized. Variations of the dipole correlation with molecular structure can explain the sometimes unexpected phase behaviour and physical properties of these substances. A qualitative model is given in terms of a monomer-dimer equilibrium. During the last decade a growing interest has developed in the 'molecular engineering' of liquid crystalline materials to obtain specific properties. Here three aspects can be distinguished: chemical properties (discussed by others at this meeting); phase behaviour, like mesomorphic temperature range and nematic-smectic behaviour; physical properties, like birefringence, dielectric anisotropy and visco-elastic properties. The demands with respect to the first two points being largely satisfied, attention has shifted to methods of influencing the physical properties. Here we can distinguish two points: the properties of the molecules themselves, and the interactions through which a molecular property influences the macroscopic behaviour. So far attention has been directed mainly towards the first of these two. However, it seems that the interactions mentioned above are far more variable than was commonly thought some years ago. This insight is mainly due to new results from the synthetic chemists, who have presented us with new mesogenic compounds that often show a behaviour that is rather unexpected from a more traditional point of view. In this paper I wish to show that many of these unexpected results can be rationalized in terms of differences in short-range correlation between the molecules. The plan of the paper is as follows. In ? 2 some of the more classical relations between molecular properties and macroscopic physical properties will be summarized. Next, in ? 3, the evidence for short-range correlations will be discussed, emphasizing results from relatively recently synthesized compounds with strongly polar end-groups like CN, saturated ring systems, or both. Finally these results are used to understand at least qualitatively some of the features of the observed phase behaviour (? 4) and of the macroscopic physical properties (? 5).

Strong spin-orbit interactions and weak antilocalization in carbon-doped p -type Ga As ∕ Al x Ga 1 − x As heterostructures

Abstract: We present a comprehensive study of the low-field magnetoresistance in carbon-doped $p$-type $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ heterostructures aiming at the investigation of spin-orbit interaction effects. The following signatures of exceptionally strong spin-orbit interactions are simultaneously observed: a beating in the Shubnikov--de Haas oscillations, a classical positive magnetoresistance due to the presence of the two spin-split subbands, and a weak antilocalization dip in the magnetoresistance. The spin-orbit-induced splitting of the heavy hole subband at the Fermi level is determined to be around 30% of the total Fermi energy. The phase-coherence length of holes of around $2.5\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ at a temperature of $70\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$, extracted from weak antilocalization measurements, is promising for the fabrication of phase-coherent $p$-type nanodevices.

Electrical properties of PZT thin films grown by sol-gel and PLD using a seed layer

Abstract: Lead Zirconate Titanate (PZT) thin films (with molar ratio of Zr:Ti::65/35) were deposited by pulsed laser deposition (PLD) and sol–gel technique on Pt/Si (1 1 1), and Pt/Si (1 0 0) substrates. A seed layer of PbTiO3 (0.1 μm) was coated by sol–gel on the substrates before depositing PZT by PLD and sol–gel. A metal/ferroelectric/metal (MFM) capacitor structure, formed by depositing gold electrode on top of the film, was used for C–V and P–E measurements. A large remnant polarization (Pr = 56.8 μC/cm2) was observed on Pt/Si (1 1 1) substrates for the films deposited by sol–gel. Comparison of properties of PZT film deposited by these two techniques is discussed.

Experimental probe of topological orders and edge excitations in the second Landau level

Abstract: This paper reports careful experiments designed to shed light on the natures of the fractional quantized Hall states observed at filling fractions 5/2, 7/3, and 8/3 in very high quality GaAs quantum wells.