Effects of interaction on an adiabatic quantum electron pump

We study the effects of inter-electron interactions on the charge pumped through an adiabatic quantum electron pump. The pumping is through a system of barriers, whose heights are deformed adiabatically. (Weak) interaction effects are introduced through a renormalisation group flow of the scattering matrices and the pumped charge is shown to {\it always} approach a quantised value at low temperatures or long length scales. The maximum value of the pumped charge is set by the number of barriers and is given by $Q_{\rm max} = n_b -1$. The correlation between the transmission and the charge pumped is studied by seeing how much of the transmission is enclosed by the pumping contour. The (integer) value of the pumped charge at low temperatures is determined by the number of transmission maxima enclosed by the pumping contour. The dissipation at finite temperatures leading to the non-quantised values of the pumped charge scales as a power law with the temperature ($Q-Q_{\rm int} \propto T^{2\alpha}$), or with the system size ($Q-Q_{\rm int} \propto L_s^{-2\alpha}$), where $\alpha$ is a measure of the interactions and vanishes at $T=0 ~(L_s=\infty)$. For a double barrier system, our result agrees with the quantisation of pumped charge seen in Luttinger liquids.Comment: 9 pages, 9 figures, better quality figures available on request from author

Effect of polyamines and natural growth substances on the growth and flowering of rose (Rosa hybrida) cv. Samurai under protected conditions

Investigations were conducted to study the effect of different polyamines and natural growth substances as a pre harvest foliar spray on greenhouse rose cv. Samurai. The study involved preharvest foliar spraying with polyamines like spermine (10 ppm) and spermidine (10 ppm); natural growth substances like enriched banana pseudostem sap (1 per cent) and cow urine (2 per cent). All the treatments improved the vegetative and flowering characters over control. However, among different treatments, foliar spray of spermine 10 ppm, followed by spermidine 10 ppm were highly significant in influencing all vegetative parameters like plant height (79 cm), number of branches per plant (3.73), stem girth (10.69 mm), number of leaves per plant (91.33), leaf area (14.68 cm2) and leaf chlorophyll content (36.96 mg/g). Further, flowering parameters like flower stalk length (61.24cm), bud length (2.70mm), flower diameter (6.50 cm), number of petals per flower (55.90) and vase life (6.63 days) were significantly maximum in plants sprayed with spermine 10ppm. The treatment of foliar spray with spermine and spermidine almost doubled the flower production and improved the flower quality in tems of bud size and vase life as compared to control

Effect of various levels of nitrogen on quantitative and qualitative parameters of Rose var. “Top Secret” under poly house condition

Study was conducted to find out the effect of various levels (100, 150, 200, 250,300 mg/plant/week) of nitrogen on growth parameters in terms of qualitative and quantitative traits of rose var. Top Secret. Plant growth in general increased with increase in nitrogen levels. Among various levels of nitrogen application, 300 mg nitrogen per plant per week significantly increased all vegetative growth parameters and showed maximum plant height (117.45 cm), leaf area (98.91 cm2 ) and a number of leaves (62.50). Further, flowering parameters like stalk length (83.53cm), bud diameter (2.45cm), bud length (2.55 cm), number of flowers per plant (7.30) as well as per square meter (53.05) were also significantly maximum in plants given nitrogen @ 300 mg per plant per week. Leaf N (2.94 %), P (0.19%), K (1.87%) and chlorophyll content in leaves (4.41mg/g) was also higher with 300 mg N per plant per week. Vase life (10 days) and anthocyanin content in petal tissue (2.09 mg/g) were found the maximum in plants given nitrogen @ 250 mg per plant per week, which was at par with the treatment of nitrogen @ 300 mg per plant per week. Nitrogen should be applied at the rate of 300 mg/plant/week under protected cultivation as the optimum dose for good plant growth and qualitative flower production in rose var. Top Secret under protected cultivation

Transport in quantum wires

With a brief introduction to one-dimensional channels and conductance quantisation in mesoscopic systems, we discuss some recent experimental puzzles in these systems, which include reduction of quantised conductances and an interesting {\it odd-even} effect in the presence of an in-plane magnetic field. We then discuss a recent non-homogeneous Luttinger liquid model proposed by us, which addresses and gives an explanation for the reduced conductances and the {\it odd-even} effect. We end with a brief summary and discussion of future projects.Comment: Talk presented at the International Discussion Meeting on Mesoscopic and Disordered systems, December, 2000, 16 pages, 2 figure

Renormalization group study of the Kondo problem at a junction of several Luttinger wires

We study a system consisting of a junction of N quantum wires, where the junction is characterized by a scalar S-matrix, and an impurity spin is coupled to the electrons close to the junction. The wires are modeled as weakly interacting Tomonaga-Luttinger liquids. We derive the renormalization group equations for the Kondo couplings of the spin to the electronic modes on different wires, and analyze the renormalization group flows and fixed points for different values of the initial Kondo couplings and of the junction S-matrix (such as the decoupled S-matrix and the Griffiths S-matrix). We generally find that the Kondo couplings flow towards large and antiferromagnetic values in one of two possible ways. For the Griffiths S-matrix, we study one of the strong coupling flows by a perturbative expansion in the inverse of the Kondo coupling; we find that at large distances, the system approaches the ferromagnetic fixed point of the decoupled S-matrix. For the decoupled S-matrix with antiferromagnetic Kondo couplings and weak inter-electron interactions, the flows are to one of two strong coupling fixed points in which all the channels are strongly coupled to each other through the impurity spin. But strong inter-electron interactions, with K_\rho < N/(N+2), stabilize a multi-channel fixed point in which the coupling between different channels goes to zero. We have also studied the temperature dependence of the conductance at the decoupled and Griffiths S-matrices.Comment: Revtex4, 16 pages including 6 figure

Transport through quasi-ballistic quantum wires: the role of contacts

We model one-dimensional transport through each open channel of a quantum wire by a Luttinger liquid with three different interaction parameters for the leads, the contact regions and the wire, and with two barriers at the contacts. We show that this model explains several features of recent experiments, such as the flat conductance plateaux observed even at finite temperatures and for different lengths, and universal conductance corrections in different channels. We discuss the possibility of seeing resonance-like structures of a fully open channel at very low temperatures.Comment: revtex, 5 pages, 1 eps figure; clarifications added in light of new experiment

Field Theories of Frustrated Heisenberg Antiferromagnets

We study the Heisenberg antiferromagnetic chain with both dimerization and frustration. The classical ground state has three phases: a Neel phase, a spiral phase and a colinear phase. In each phase, we discuss a non-linear sigma model field theory governing the low energy excitations. We study the theory in the spiral phase in detail using the renormalization group. The field theory, based on an $SO(3)$ matrix-valued field, becomes $SO(3) \times SO(3)$ and Lorentz invariant at long distances where the elementary excitation is analytically known to be a massive spin-$1/2$ doublet. The field theory supports $Z_2 ~$ solitons which lead to a double degeneracy in the spectrum for half-integer spins (when there is no dimerization).Comment: Latex, 12 pages, 2 figures (gzipped and uuencoded

Junction of several weakly interacting quantum wires: a renormalization group study

We study the conductance of three or more semi-infinite wires which meet at a junction. The electrons in the wires are taken to interact weakly with each other through a short-range density-density interaction, and they encounter a general scattering matrix at the junction. We derive the renormalization group equations satisfied by the S-matrix, and we identify its fixed points and their stabilities. The conductance between any pair of wires is then studied as a function of physical parameters such as temperature. We discuss the possibility of observing the effects of junctions in present day experiments, such as the four-terminal conductance of a quantum wire and crossed quantum wires.Comment: RevTeX, 13 pages, including 4 eps figure

Bosonic Mean Field Theory of the Spiral Phases of Heisenberg Antiferromagnets on a Chain

We develop a novel bosonic mean field theory to describe the spiral phases of a Heisenberg antiferromagnet on a one-dimensional chain, in terms of three bosons at each site. The ground state is disordered and for large values of the spin $S$, two different and exponentially small energy gaps are found. The spin-spin correlation function is computed and is shown to decay exponentially at large distances. Our mean field theory is also shown to be exact in a large-$N$ generalization.Comment: plain.tex, TIFR/TH/92-66, IISc/CTS/92-1