Quasiparticle scattering from vortices in d-wave superconductors I: Superflow contribution

In the vortex state of a d-wave superconductor, massless Dirac quasiparticles are scattered from magnetic vortices via a combination of two basic mechanisms: effective potential scattering due to the superflow swirling about the vortices and Aharonov-Bohm scattering due to the Berry phase acquired by a quasiparticle upon circling a vortex. In this paper, we study the superflow contribution by calculating the differential cross section for a quasiparticle scattering from the effective non-central potential of a single vortex. We solve the massless Dirac equation in polar coordinates and obtain the cross section via a partial wave analysis. We also present a more transparent Born-limit calculation and in this approximation we provide an analytic expression for the differential cross section. The Berry phase contribution to the quasiparticle scattering is considered in a separate paper.Comment: 22 pages, 6 figure

Force calculation on walls and embedded particles in multiparticle collision dynamics simulations

Colloidal solutions posses a wide range of time and length scales, so that it is unfeasible to keep track of all of them within a single simulation. As a consequence some form of coarse-graining must be applied. In this work we use the Multi-Particle Collision Dynamics scheme. We describe a particular implementation of no-slip boundary conditions upon a solid surface, capable of providing correct force s on the solid bypassing the calculation of the velocity profile or the stre ss tensor in the fluid near the surface. As an application we measure the friction on a spherical particle, when it is placed in a bulk fluid and when it is confined in a slit. We show that the implementation of the no-slip boundary conditions leads to an enhanced Ensko g friction, which can be understood analytically. Because of the long-range nature of hydrodynamic interactions, the Stokes friction obtained from the simulations is sensitive of the simulation box size. We address this topic for the slit geometry, showing that that the dependence on the system size differs very much from what is expected in a 3D system, where periodic boundary conditions are used in all directions.Comment: To appear in Physical Review

Weak-Field Thermal Hall Conductivity in the Mixed State of d-Wave Superconductors

Thermal transport in the mixed state of a d-wave superconductor is considered within the weak-field regime. We express the thermal conductivity, $\kappa_{xx}$, and the thermal Hall conductivity, $\kappa_{xy}$, in terms of the cross section for quasiparticle scattering from a single vortex. Solving for the cross section (neglecting the Berry phase contribution and the anisotropy of the gap nodes), we obtain $\kappa_{xx}(H,T)$ and $\kappa_{xy}(H,T)$ in surprisingly good agreement with the qualitative features of the experimental results for YBa$_{2}$Cu$_{3}$O$_{6.99}$. In particular, we show that the simple, yet previously unexpected, weak-field behavior, $\kappa_{xy}(H,T) \sim T\sqrt{H}$, is that of thermally-excited nodal quasiparticles, scattering primarily from impurities, with a small skew component provided by vortex scattering.Comment: 5 pages, 2 figures; final version as published in Phys Rev Let

Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots

We investigate the influence of an external magnetic field on spin phase relaxation of single electrons in semiconductor quantum dots induced by the hyperfine interaction. The basic decay mechanism is attributed to the dispersion of local effective nuclear fields over the ensemble of quantum dots. The characteristics of electron spin dephasing is analyzed by taking an average over the nuclear spin distribution. We find that the dephasing rate can be estimated as a spin precession frequency caused primarily by the mean value of the local nuclear magnetic field. Furthermore, it is shown that the hyperfine interaction does not fully depolarize electron spin. The loss of initial spin polarization during the dephasing process depends strongly on the external magnetic field, leading to the possibility of effective suppression of this mechanism.Comment: 10 pages, 2 figure

The microwave induced resistance response of a high mobility 2DEG from the quasi-classical limit to the quantum Hall regime

Microwave induced resistance oscillations (MIROs) were studied experimentally over a very wide range of frequencies ranging from ~20 GHz up to ~4 THz, and from the quasi-classical regime to the quantum Hall effect regime. At low frequencies regular MIROs were observed, with a periodicity determined by the ratio of the microwave to cyclotron frequencies. For frequencies below 150 GHz the magnetic field dependence of MIROs waveform is well described by a simplified version of an existing theoretical model, where the damping is controlled by the width of the Landau levels. In the THz frequency range MIROs vanish and only pronounced resistance changes are observed at the cyclotron resonance. The evolution of MIROs with frequency are presented and discussed.Comment: 4 pages, presented at EP2DS, to be published in Physica

Effects of an in-plane magnetic field on c-axis sum rule and superfluid density in high-TcT_{c} cuprates

In layered cuprates, the application of an in-plane magnetic field $({\bf H})$ changes the c-axis optical sum rule and superfluid density $\rho_{s}$. For pure incoherent c-axis coupling, ${\bf H}$ has no effect on either quantities but it does if an additional coherent component is present. For the coherent contribution, different characteristic variations on ${\bf H}$ and on temperature result from the constant part $(t_{\perp})$ of the hopping matrix element and from the part $(t_{\phi})$ which has zero on the diagonal of the Brillouin zone. Only the constant part $(t_{\perp})$ leads to a dependence on the direction of ${\bf H}$ as well as on its magnitude.Comment: 3 figure

Formation of d-wave superconducting order in a randomly doped lattice

We consider the interplay between superconducting coupling and dopant impurity scattering of charge carriers in planar square lattice systems and examine physical conditions (doping level, temperature, local symmetry of coupling and scattering potentials) necessary in this model system to obtain a d-wave superconducting order, like that observed in real doped cuprate HTSC materials. Using the Lifshitz model for the disorder introduced into system by dopants, we analyze also the non-uniform structure of such d-wave parameter, including both its magnitude and phase variation. The results indicate that d-wave superconductivity turns possible in a doped metal until it can be destroyed at too high doping levels.Comment: 22 pages, 2 figure

Microwave Photoconductivity in Two-Dimensional Electron Systems due to Photon-Assisted Interaction of Electrons with Leaky Interface Phonons

We calculate the contribution of the photon-assisted interaction of electrons with leaky interface phonons to the dissipative dc photoconductivity of a two-dimensional electron system in a magnetic field. The calculated photoconductivity as a function of the frequency of microwave radiation and the magnetic field exhibits pronounced oscillations. The obtained oscillation structure is different from that in the case of photon-assisted interaction with impurities. We demonstrate that at a sufficiently strong microwave radiation in the certain ranges of its frequency (or in certain ranges of the magnetic field) this mechanism can result in the absolute negative conductivity.Comment: 3 pages, 1 figur

Archaeological Investigations at Four San Antonio Missions: Mission Trails Underground Conversion Project

This report contains the results of archaeological work performed by the Center for Archaeological Research (CAR) at The University of Texas San Antonio (UTSA) for City Public Service (CPS). The archaeological investigation and monitoring for the Mission Trails Underground Conversion Project was carried out under Texas Historical Commission (THC) Permit Number: 2020, and the work was conducted at each of the four historical San Antonio missions which make up San Antonio Missions National Historical Park. The Mission Trails Underground Conversion Project was created to enhance and upgrade electrical and utility connections by replacing aboveground connections with underground connections at each ofthe four missions. Mission San Juan (41BX5)-In October of 1998, personnel from CAR began archaeological investigations at Mission San Juan Capistrano in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. The purpose of the investigation was to test for intact, buried cultural features in advance of trenching activities involved in the relocation of utility lines and connections. CAR archaeologists developed a plan regarding the area to be impacted which included ten 1 x 1-m excavations units and a series of twelve shovel tests along the proposed path of the utility trench. Excavation units uncovered evidence of existing buildings, wall foundations and Colonial-period flooring episodes, revealing new data west of the known structures and not previously accounted for. Further excavations are warranted to determine the nature of features such as a Colonial-period wall revealed near one of the excavation units. This material discovered by the archaeological investigations resulted in the altering of the projected utility trench alignment to avoid disturbing deposits. Further archaeological investigations are recommended for the newly revealed features. Mission San Jose (41BX3)- In January of 1999, personnel from CAR began archaeological investigations at Mission San Jose y San Miguel de Aguayo in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. The purpose of the investigation was to test for intact, buried cultural features in advance of trenching activities involved in the relocation of utility lines and connections. CAR archaeologists conducted a series of shovel tests along the center-lines of the proposed utility trenches to identifY areas of possible impact to intact Spanish Colonial cultural materials. In addition to shovel testing, monitoring of the trenching was conducted in areas where the possibility of impacting cultural material was high. An early-twentieth century trash midden was encountered during monitoring of the trench where it paralleled the Service Drive in the northwest comer of the Mission compound. This material did not warrant altering the course of the trench, and no further archaeological work is recommended at this time. Mission Concepcion (41BX12)- In January of 1999, personnel from CAR began archaeological investigations at Mission Nuestra Senora de la Purisima Concepcion as part of the Mission Trails Underground Conversion Project. A construction crew, while excavating a manhole designed to provide access to underground electrical utilities, had unearthed a large number of animal bones. After concluding a large feature had been unexpectedly impacted, CAR conducted test excavations to ascertain the nature of this feature. It was determined to be a section of an acequia which had been refilled during the Colonial period with construction debris and trash, including a large number of animal bones. Test units and the original manhole excavations allowed for a profile of the acequia to be constructed. This information combined with previous archaeological work and historical research, allowed a tentative proposal on the sequence of acequia construction and re-routing for the Concepcion mission. Monitoring of other underground work conducted in the area resulted in the discovery of a location of a Colonial-period wall, southeast of the Visitors\u27 Center, which may be a portion of the original south wall of the mission. It is recommended that if any further work is required, consideration should be given to testing and/or monitoring to reduce the risk of negative impact to historic remains. Mission Espada (41BX4)- In July of 1999, personnel from CAR began archaeological investigations at Mission San Francisco de la Espada in advance of the proposed installation of underground utility lines for the Mission Trails Underground Conversion Project. From initial discussions, it was noted that the proximity of the proposed route of the underground utility trench could have an impact on the old compound walls of the mission and the path was altered to avoid any possible impact. A series of thirteen shovel tests were conducted in advance along the altered path of the proposed utility trench as it progressed from the southwest comer of the mission compound across the dry irrigation ditch or acequia to the northwest. Monitoring of the trenching activities followed with no significant deposits being exposed. No further work is recommended within the project area, but if future construction is to occur in the area between the utility trench and the Church at Mission Espada, monitoring should then be considered