132 research outputs found
Comment on "Spin Transport properties of the quantum one-dimensional non-linear sigma model"
In a recent preprint (cond-mat/9905415), Fujimoto has used the Bethe ansatz
to compute the finite temperature, zero frequency Drude weight of spin
transport in the quantum O(3) non-linear sigma model in a magnetic field . We show here that, contrary to his claims, the results are in accord
with earlier semiclassical results (Sachdev and Damle, cond-mat/9610115). We
also comment on his 1/N expansion, and show that it does not properly describe
the long-time correlations.Comment: 4 page
Evaluation of Taro (Colocasia esculenta L.) Cultivars for Growth, Yield and Quality Attributes
A study on varietal evaluation in taro for growth, yield and quality attributes was carried out in a replicated experiment and morphological and chemical analysis was done. Significant differences were recorded for all the characteristics studied. 'Panchmukhi' recorded highest plant height (179.33cm), petiole length (153.11cm), petiole breadth (13.87mm) and leaf size (3095.67cm2), LAI (1.14), corm length (152.41mm) and breadth (107.77mm), average corm weight (1500.00g) and corm yield (20.00t/ha). 'C-3' recorded maximum (15.00) petiole number and cormel length (85.93mm). Cormel yield (15.29t/ha), total yield (25.92t/ha) and number of cormels per plant (30.33) was found to be maximum in cv. White Gouriya. 'ML-2' recorded maximum (7.33) number of side shoots. Highest average cormel weight (72.85g) was maximum in cv. Arcol-7, and 'Arcol-5' recorded maximum (67.43mm) cormel breadth; the least blight incidence percentage (8.00) was recorded in 'Nayabungalow'. As for biochemical constituents, 'Nainital' recorded the highest (5.85%) total sugars, 'Kandha-5' exhibited the highest (34.67%) starch content and 'Nadia Local' with showed highest levels of oxalic acid (1.05mg/100g). Highest dry matter content (27.50%) was recorded in cvs. KCA-1 and Panchmukhi, while the highest moisture percentage (82.83) was recorded in 'IG Coll-5'
17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K
We used 17O NMR to probe the uniform (wavevector q=0) electron spin
excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pm\pi/a
staggered components. Our results support the logarithmic decrease of the
uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement
of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation
rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic
at the T=0 limit, but has a diffusion-like contribution at finite temperatures
even for T << J.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figure
Duality of switching mechanisms and transient negative capacitance in improper ferroelectrics
The recent discovery of transient negative capacitance has sparked an intense
debate on the role of homogeneous and inhomogeneous mechanisms in polarizations
switching. In this work, we report observation of transient negative
capacitance in improper ferroelectric h-YbFeO3 films in a resistor-capacitor
circuit, and a concaved shape of anomaly in the voltage wave form, in the early
and late stage of the polarizations switching respectively. Using a
phenomenological model, we show that the early-stage negative capacitance is
likely due to the inhomogeneous switching involving nucleation and domain wall
motion, while the anomaly at the late stage, which appears to be a reminiscent
negative capacitance is the manifestation of the thermodynamically unstable
part of the free-energy landscape in the homogeneous switching. The complex
free-energy landscape in hexagonal ferrites may be the key to cause the abrupt
change in polarization switching speed and the corresponding anomaly. These
results reconcile the two seemingly conflicting mechanisms in the polarization
switching and highlight their different roles at different stages. The unique
energy-landscape in hexagonal ferrites that reveals the dual switching
mechanism suggests the promising application potential in terms of negative
capacitance.Comment: 14 pages,5 figure
63Cu NQR evidence of dimensional crossover to anisotropic 2d regime in S= 1/2 three-leg ladder Sr2Cu3O5
We probed spin-spin correlations up to 725 K with 63Cu NQR in the S= 1/2
three-leg ladder Sr2Cu3O5. We present experimental evidence that below 300 K,
weak inter-ladder coupling causes dimensional crossover of the spin-spin
correlation length \xi from quasi-1d (\xi ~ 1/T) to anisotropic 2d regime (\xi
\~ exp[2\pi\rho_{s}/T], where 2\pi\rho_{s} = 290 +/- 30 K is the effective spin
stiffness). This is the first experimental verification of the renormalized
classical behavior of the anisotropic non-linear sigma model in 2d, which has
been recently proposed for the striped phase in high T_{c} cuprates.Comment: 4 pages, 3 figure
Intermediate temperature dynamics of one-dimensional Heisenberg antiferromagnets
We present a general theory for the intermediate temperature (T) properties
of Heisenberg antiferromagnets of spin-S ions on p-leg ladders, valid for 2Sp
even or odd. Following an earlier proposal for 2Sp even (Damle and Sachdev,
cond-mat/9711014), we argue that an integrable, classical, continuum model of a
fixed-length, 3-vector applies over an intermediate temperature range; this
range becomes very wide for moderate and large values of 2Sp. The coupling
constants of the effective model are known exactly in terms of the energy gap
above the ground state (for 2Sp even) or a crossover scale (for 2Sp odd).
Analytic and numeric results for dynamic and transport properties are obtained,
including some exact results for the spin-wave damping. Numerous quantitative
predictions for neutron scattering and NMR experiments are made. A general
discussion on the nature of T>0 transport in integrable systems is also
presented: an exact solution of a toy model proves that diffusion can exist in
integrable systems, provided proper care is taken in approaching the
thermodynamic limit.Comment: 38 pages, including 12 figure
Hydrodynamics of R-charged D1-branes
We study the hydrodynamic properties of strongly coupled Yang-Mills
theory of the D1-brane at finite temperature and at a non-zero density of
R-charge in the framework of gauge/gravity duality. The gravity dual
description involves a charged black hole solution of an
Einstein-Maxwell-dilaton system in 3 dimensions which is obtained by a
consistent truncation of the spinning D1-brane in 10 dimensions. We evaluate
thermal and electrical conductivity as well as the bulk viscosity as a function
of the chemical potential conjugate to the R-charges of the D1-brane. We show
that the ratio of bulk viscosity to entropy density is independent of the
chemical potential and is equal to . The thermal conductivity and bulk
viscosity obey a relationship similar to the Wiedemann-Franz law. We show that
at the boundary of thermodynamic stability, the charge diffusion mode becomes
unstable and the transport coefficients exhibit critical behaviour. Our method
for evaluating the transport coefficients relies on expressing the second order
differential equations in terms of a first order equation which dictates the
radial evolution of the transport coefficient. The radial evolution equations
can be solved exactly for the transport coefficients of our interest. We
observe that transport coefficients of the D1-brane theory are related to that
of the M2-brane by an overall proportionality constant which sets the
dimensions.Comment: 57 pages, 12 figure
Quantum impurity dynamics in two-dimensional antiferromagnets and superconductors
We present the universal theory of arbitrary, localized impurities in a
confining paramagnetic state of two-dimensional antiferromagnets with global
SU(2) spin symmetry. The energy gap of the host antiferromagnet to spin-1
excitations, \Delta, is assumed to be significantly smaller than a typical
nearest neighbor exchange. In the absence of impurities, it was argued in
earlier work (Chubukov et al. cond-mat/9304046) that the low-temperature
quantum dynamics is universally and completely determined by the values of
\Delta and a spin-wave velocity c. Here we establish the remarkable fact that
no additional parameters are necessary for an antiferromagnet with a dilute
concentration of impurities, n_{imp} - each impurity is completely
characterized by a integer/half-odd-integer valued spin, S, which measures the
net uncompensated Berry phase due to spin precession in its vicinity. We
compute the impurity-induced damping of the spin-1 collective mode of the
antiferromagnet: the damping occurs on an energy scale \Gamma= n_{imp} (\hbar
c)^2/\Delta, and we predict a universal, asymmetric lineshape for the
collective mode peak. We argue that, under suitable conditions, our results
apply unchanged (or in some cases, with minor modifications) to d-wave
superconductors, and compare them to recent neutron scattering experiments on
YBCO by Fong et al. (cond-mat/9812047). We also describe the universal
evolution of numerous measurable correlations as the host antiferromagnet
undergoes a quantum phase transition to a Neel ordered state.Comment: 36 pages, 12 figures; added reference
Mechanistic insight into the sensing of nitroaromatic compounds by metal-organic frameworks
There has been extensive research on the sensing of explosive nitroaromatic compounds (NACs) using fluorescent metal-organic frameworks (MOFs). However, ambiguity in the sensing mechanism has hampered the development of efficient explosive sensors. Here we report the synthesis of a hydroxyl-functionalized MOF for rapid and efficient sensing of NACs and examine in detail its fluorescence quenching mechanisms. In chloroform, quenching takes place primarily by exciton migration to the ground-state complex formed between the MOF and the analytes. A combination of hydrogen-bonding interactions and ??????? stacking interactions are responsible for fluorescence quenching, and this observation is supported by single-crystal structures. In water, the quenching mechanism shifts toward resonance energy transfer and photo-induced electron transfer, after exciton migration as in chloroform. This study provides insight into florescence-quenching mechanisms for the selective sensing of NACs and reduces the ambiguity regarding the nature of interactions between the MOF and NACs
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