Thermodynamic basis of the concept of "recombination resistances"

The concept of "recombination resistance" introduced by Shockley and Read (Phys. Rev. 87, 835 (1952)) is discussed within the framework of the thermodynamics of irreversible processes ruled by the principle of the minimum rate of entropy production. It is shown that the affinities of recombination processes represent "voltages" in a thermodynamic Ohm-like law where the net rates of recombinations represent the "currents". The quantities thus found allow for the definition of the "dissipated power" which is to be related to the rate of entropy production of the recombination processes dealt with.Comment: Submitted to Phys. Rev.

Long range order and two-fluid behavior in heavy electron materials

The heavy electron Kondo liquid is an emergent state of condensed matter that displays universal behavior independent of material details. Properties of the heavy electron liquid are best probed by NMR Knight shift measurements, which provide a direct measure of the behavior of the heavy electron liquid that emerges below the Kondo lattice coherence temperature as the lattice of local moments hybridizes with the background conduction electrons. Because the transfer of spectral weight between the localized and itinerant electronic degrees of freedom is gradual, the Kondo liquid typically coexists with the local moment component until the material orders at low temperatures. The two-fluid formula captures this behavior in a broad range of materials in the paramagnetic state. In order to investigate two-fluid behavior and the onset and physical origin of different long range ordered ground states in heavy electron materials, we have extended Knight shift measurements to URu$_2$Si$_2$, CeIrIn$_5$ and CeRhIn$_5$. In CeRhIn$_5$ we find that the antiferromagnetic order is preceded by a relocalization of the Kondo liquid, providing independent evidence for a local moment origin of antiferromagnetism. In URu$_2$Si$_2$ the hidden order is shown to emerge directly from the Kondo liquid and so is not associated with local moment physics. Our results imply that the nature of the ground state is strongly coupled with the hybridization in the Kondo lattice in agreement with phase diagram proposed by Yang and Pines.Comment: 9 pages, 13 figure

Vector like gauge theories with almost massless fermions on the lattice

A truncation of the overlap (domain wall fermions) is studied and a criterion for reliability of the approximation is obtained by comparison to the exact overlap formula describing massless quarks. We also present a truncated version of regularized, pure gauge, supersymmetric models. The mechanism for generating almost masslessness is shown to be a generalized see-saw which can also be viewed as a version of Froggatt-Nielsen's method for obtaining natural large mass hierarchies. Viewed in this way the mechanism preserving the mass hierarchy naturally avoids preserving even approximately axial U(1). The new insights into the source of the mass hierarchy suggest ways to increase the efficiency of numerical simulations of QCD employing the truncated overlap.Comment: 35 pages, TeX, 4 figures using eps

Connectivity of Growing Random Networks

A solution for the time- and age-dependent connectivity distribution of a growing random network is presented. The network is built by adding sites which link to earlier sites with a probability A_k which depends on the number of pre-existing links k to that site. For homogeneous connection kernels, A_k ~ k^gamma, different behaviors arise for gamma1, and gamma=1. For gamma<1, the number of sites with k links, N_k, varies as stretched exponential. For gamma>1, a single site connects to nearly all other sites. In the borderline case A_k ~ k, the power law N_k ~k^{-nu} is found, where the exponent nu can be tuned to any value in the range 2<nu<infinity.Comment: 4 pages, 2 figures, 2 column revtex format final version to appear in PRL; contains additional result

Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy

We report the results of a cryogenic study of the modification of YBa2Cu3O7-delta surface electronic properties with the probe of a scanning tunneling microscope (STM). A negative voltage applied to the sample during STM tunneling is found to modify locally the conductance of the native degraded surface layer. When the degraded layer is removed by etching, the effect disappears. An additional surface effect is identified using Scanning Kelvin Probe Microscopy in combination with STM. We observe reversible surface charging for both etched and unetched samples, indicating the presence of a defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and Technolog

Time-Dependent Current Partition in Mesoscopic Conductors

The currents at the terminals of a mesoscopic conductor are evaluated in the presence of slowly oscillating potentials applied to the contacts of the sample. The need to find a charge and current conserving solution to this dynamic current partition problem is emphasized. We present results for the electro-chemical admittance describing the long range Coulomb interaction in a Hartree approach. For multiply connected samples we discuss the symmetry of the admittance under reversal of an Aharonov-Bohm flux.Comment: 22 pages, 3 figures upon request, IBM RC 1971

Stationary states and phase diagram for a model of the Gunn effect under realistic boundary conditions

A general formulation of boundary conditions for semiconductor-metal contacts follows from a phenomenological procedure sketched here. The resulting boundary conditions, which incorporate only physically well-defined parameters, are used to study the classical unipolar drift-diffusion model for the Gunn effect. The analysis of its stationary solutions reveals the presence of bistability and hysteresis for a certain range of contact parameters. Several types of Gunn effect are predicted to occur in the model, when no stable stationary solution exists, depending on the value of the parameters of the injecting contact appearing in the boundary condition. In this way, the critical role played by contacts in the Gunn effect is clearly stablished.Comment: 10 pages, 6 Post-Script figure

Theory of electrical spin injection: Tunnel contacts as a solution of the conductivity mismatch problem

Theory of electrical spin injection from a ferromagnetic (FM) metal into a normal (N) conductor is presented. We show that tunnel contacts (T) can dramatically increase spin injection and solve the problem of the mismatch in the conductivities of a FM metal and a semiconductor microstructure. We also present explicit expressions for the spin-valve resistance of FM-T-N- and FM-T-N-T-FM-junctions with tunnel contacts at the interfaces and show that the resistance includes both positive and negative contributions (Kapitza resistance and injection conductivity, respectively).Comment: 4 pages, to appear in Phys. Rev. B (rapid communications