Exactly solvable random matrix models with additional two-body interactions

It has been argued that despite remarkable success, existing random matrix theories are not adequate to describe disordered conductors in the metallic regime, due to the presence of certain two-body interactions in the effective Hamiltonian for the eigenvalues, in addition to the standard logarithmic interaction that arises entirely from symmetry considerations. We present a new method that allows exact solution of random matrix models with such additional two-body interactions. This should broaden the scope of random matrix models in general.Comment: 12 pages, late

Distribution function for shotnoise in disordered multi-channel quantum conductors

We obtain the shot noise generating function for a multi-channel quantum conductor in the diffusive limit.Comment: 8, late

Universality of phonon transport in surface-roughness dominated nanowires

We analyze, both theoretically and numerically, the temperature dependent thermal conductivity \k{appa} of two-dimensional nanowires with surface roughness. Although each sample is characterized by three independent parameters - the diameter (width) of the wire, the correlation length and strength of the surface corrugation - our theory predicts that there exists a universal regime where \k{appa} is a function of a single combination of all three model parameters. Numerical simulations of propagation of acoustic phonons across thin wires confirm this universality and predict a d 1/2 dependence of \k{appa} on the diameter d

Distribution of conductance for Anderson Insulators: A theory with a single parameter

We obtain an analytic expression for the full distribution of conductance for a strongly disordered three dimensional conductor within a perturbative approach based on the transfer-matrix formulation. Our results confirm numerical evidence that the log-normal limit of the distribution is not reached even in the deeply insulating regime. We show that the variance of the logarithm of the conductance scales as a fractional power of the mean, while the skewness changes sign as one approaches the Anderson metal-insulator transition from the deeply insulating limit, all described as a function of a single parameter. The approach suggests a possible single parameter description of the Anderson transition that takes into account the full nontrivial distribution of conductance.Comment: 4 pages, 4 figure

Suppressing phonon transport in nanowires: a simple model for phonon-surface roughness interaction

Suppressing phonon propagation in nanowires is an essential goal towards achieving efficient thermoelectric devices. Recent experiments have shown unambiguously that surface roughness is a key factor that can reduce the thermal conductivity well below the Casimir limit in thin crystalline silicon nanowires. We use insights gained from the experimental studies to construct a simple analytically tractable model of the phonon-surface roughness interaction that provides a better theoretical understanding of the effects of surface roughness on the thermal conductivity, which could potentially help in designing better thermoelectric devices.Comment: 7 pages, 3 figures; accepted for publication in Phys. Rev.

Phonon localization in surface-roughness dominated nanowires

Studies of possible localization of phonons in nanomaterials have gained importance in recent years in the context of thermoelectricity where phonon-localization can reduce thermal conductivity, thereby improving the efficiency of thermoelectric devices. However, despite significant efforts, phonon-localization has not yet been observed experimentally in real materials. Here we propose that surface-roughness dominated nanowires are ideal candidates to observe localization of phonons, and show numerically that the space and time evolution of the energy generated by a heat-pulse injected at a given point shows clear signatures of phonon localization. We suggest that the same configuration might allow experimental observation of localization of phonons. Our results confirm the universality in the surface-roughness dominated regime proposed earlier, which allows us to characterize the strength of disorder by a single parameter combining the width of the wire as well as the mean height of the corrugation and its correlation length

Conductance distribution in quasi-one-dimensional disordered quantum wires

We develop a simple systematic method, valid for all strengths of disorder, to obtain analytically the full distribution of conductances P(g) for a quasi one dimensional wire within the model of non-interacting fermions. The method has been used in [1-3] to predict sharp features in P(g) near g=1 and the existence of non-analyticity in the conductance distribution in the insulating and crossover regimes, as well as to show how P(g) changes from Gaussian to log-normal behavior as the disorder strength is increased. Here we provide many details of the method, including intermediate results that offer much insight into the nature of the solutions. In addition, we show within the same framework that while for metals P(g) is a Gaussian around g >>1, there exists a log-normal tail for g << 1, consistent with earlier field theory calculations. We also obtain several other results that compare very well with available exact results in the metallic and insulating regimes.Comment: 9 figures, 50 pages (figures included). To appear in Annals of Physic

Conductance distribution in strongly disordered mesoscopic systems in three dimensions

Recent numerical simulations have shown that the distribution of conductance P(g) in 3D strongly localized regiem differs significally from the expected log normal distribution. To understand the origin of this difference analytically, we used a generalized DMPK equation for the joint probablity distribution of the transmission eigenvalues which includes a phenomenological (disorder and dimensionality dependent) matrix K containing certain correlations of the transfer matrices. We first of all examine the assumptions made in the derivation if the generalized DMPK and find that to a good approximation they remain valid in 3D. We then evaluate the matrix K numerically for various strength of the disorder and various system sizes. In the strong disorder limit we find that K can be described by a simple model which, for a cubic system, depends on a single parameter. We use this phenomenological model to analytically evaluate the full distribution P(g) for Anderson insulators in 3D. The analytic results allow us to develop an intuitive understanding of the entire distribution, which differs qualitatively from the log-normal distribution of a Q1D wire. We also show that out method could be applicable in the critical regime of the Anderson transition

Non-linear thermoelectric transport: A class of nano-devices for high efficiency and large power output

Molecular junctions and similar devices described by an energy dependent transmission coefficient can have a high linear response thermoelectric figure of merit. Since such devices are inherently non-linear, the full thermodynamic efficiency valid for any temperature and chemical potential difference across the leads is calculated. The general features in the energy dependence of the tranmission function that lead to high efficiency and also high power output are determined. It is shown that the device with the highest efficiency does not necessarily lead to large power output. To illustrate this, we use a model called the t-stub model representing tunneling through an energy level connected to another energy level. Within this model both high efficiency and high power output are achievable. Futhermore, by connecting many nanodevices it is shown to be possible to scale up the power output without compromising efficiency in an (exactly solvable) n-channel model even with tunneling between the devices.Comment: References added, minor corrections; published versio

Electric field induced memory and aging effects in pure solid N_2

We report combined high sensitivity dielectric constant and heat capacity measurements of pure solid N_2 in the presence of a small external ac electric field in the audio frequency range. We have observed strong field induced aging and memory effects which show that field cooled samples may be prepared in a variety of metastable states leading to a free energy landscape with experimentally ``tunable'' barriers, and tunneling between these states may occur within laboratory time scales.Comment: 4 pages, 3 figure