R. Dynes - Academia.edu (original) (raw)
Papers by R. Dynes
Physical Review, 1968
We have calculated the phonon-limited resistivity of a number of simple metals. Information about... more We have calculated the phonon-limited resistivity of a number of simple metals. Information about the lattice dynamics is taken from inelastic neutron scattering experiments. l'rom a Born-von KArman forceconstant 6t to the data, we compute the solid structure factor as a function of temperature using a onephonon approximation. This should be adequate for the relatively low temperatures considered in this work. The resistivity is given simply as a quadrature of the structure factor times the square of the electron-ion pseudopotential form factor, which we take to be of the Heine-Abarenkov form. Good agreement is obtained with experiment for both absolute value and detailed variation with temperature.
The current-voltage characteristics (I-V) of some metal-barrier Josephson junctions include a cur... more The current-voltage characteristics (I-V) of some metal-barrier Josephson junctions include a current component that does not exhibit the DC, or AC Josephson effects. This current is referred to as the excess current, I χ. Moreover, while I χ is negligible around the transition temperature T C , it increases and can exceed 50% of the total current as temperature is decreased. Normally, I χ is omitted from Josephson I-V models and this leads to a large overestimate of the product of Josephson critical current, I C , and normal-state resistance, R N (i.e., I C R N). We have developed an extended I-V model based on the Stewart-McCumber and Ambegaokar-Halperin models that includes I χ. Using our model, we fit experimental I-V data for planar Y-Ba-Cu-O junctions over a range of temperatures. From these fits we obtain values for I χ , I C and R N , as well as noise temperature. Our values agree well with experimental measurements. I C is suppressed using a magnetic field. Further, our I C exhibits an asymptotic temperature dependence like that expected for a superconducting energy gap well below T C. Our model is an improvement over existing models as it reliably estimates I C R N .
Surface Science, 1984
We report experiments on the propagation of ballistic phonons through the (001) inversion layer o... more We report experiments on the propagation of ballistic phonons through the (001) inversion layer of Si. An attenuation is observed which is an order of magnitude larger than can be accounted for by absorption alone. A new, dynamical phonon scattering theory is presented which provides an explanation.
Surface Science, 1982
Measurements of the absorption of ballistic phonons by the twodimensional electron gas (2DEG) in ... more Measurements of the absorption of ballistic phonons by the twodimensional electron gas (2DEG) in the inversion layer of a Si MOSFET are presented and compared with theory.
Physical Review Letters, 1992
The induced magnetization of an isotropic type-II superconductor with an anisotropic sample shape... more The induced magnetization of an isotropic type-II superconductor with an anisotropic sample shape has been measured in an oblique magnetic field and separated into its reversible and irreversible contributions. The measurements unexpectedly show that the irreversible magnetization is oriented essentially parallel to the smallest sample dimension, and is almost independent of the angle of the applied field. This behavior can be understood by considering the critical-state model when the applied field is at an arbitrary direction with respect to the sample axes.
![Research paper thumbnail of Erratum: Universal transport in two-dimensional granular superconductors [Phys. Rev. B 66, 052509 (2002)]](https://attachments.academia-assets.com/115697281/thumbnails/1.jpg)
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IEEE Transactions on Magnetics, 1977
We have fabricated thin films of Nb3Ge, Nb3Sn, V3Si and V3Ge and investigated their superconducti... more We have fabricated thin films of Nb3Ge, Nb3Sn, V3Si and V3Ge and investigated their superconducting and structural properties. In the case of the Nb compounds the dependence of Tc, resistance ratio and phase on stoichiometry have been determined. Defects have also been introduced into these films, in a controlled fashion, by irradiation with 1.9 MeV4He particles, and the structural and
IEEE Transactions on Applied Superconductivity, 2013
The voltage as a function of applied magnetic field (V-B) was calculated for arrays of supercondu... more The voltage as a function of applied magnetic field (V-B) was calculated for arrays of superconducting quantum interference devices (SQUIDs) connected in series. Comparisons were made between arrays of equal area SQUIDs and superconducting quantum interference filters (SQIFs). The areas for the SQIFs were varied exponentially, so that the V-B had a sharp minimum at zero field. We used equations for the dc SQUID based on resistively shunted junctions, with typical parameters for YBa2Cu3O7 - δ ion damage Josephson junctions. The maximum transfer coefficient of the central minimum VB = (∂V/∂B)max of the SQIF decreases as the area range increases. We find that the equal area array is more robust to the effects of non-uniform junction critical currents than the SQIF, for the junction parameters and SQUID area distributions chosen. Furthermore, we find that slight variations (~5%) to the area due to fabrication irregularities have little effect on the central minimum of V-B for either device.
The "restless" trajectory of my career from physics undergraduate to university president follows... more The "restless" trajectory of my career from physics undergraduate to university president follows the nature of physics itself. In physics, you are constantly seeking challenges, experimenting, creating hypotheses, looking for and finding solutions. I recall having a structured view of the world as a boy, a sense that there was a guiding "master plan" to most things and that wise, educated, benevolent people were there to implement the plan. "They" would do the right thing. Along the way, I realized, "there is no 'they' there; there is only us." Acknowledging the laws of thermodynamics-"you can't win, you can't break even, and you can't get out of the game"-I nonetheless believe that if you have a restless mind, an open heart, and intellectual honesty without giving into wishful thinking, physicists can do anything. .
the years to come, the size and cost of cryo-coolers will get smaller and the demand for a VLSI J... more the years to come, the size and cost of cryo-coolers will get smaller and the demand for a VLSI Josephson junction technology will increase. One possible candidate to fill this need is the "ion-damage" Josephson junction. These junctions are fabricated by using ion bombardment to create localized narrow regions of defects in the plane of a thin film of superconductor. These regions have a superconducting transition temperature lower than that of the bulk film and act as hysteretic Josephson junctions. The advantage of these junctions over other technologies is that they have no interfaces between different materials, and can be placed over 10 times closer to each other in comparison to competing techniques. Individual junctions and series arrays were fabricated from YBCO and magnesium diboride. Junction current-voltage characteristics near the critical temperature follow the resistively shunted junction model however at lower temperatures the barrier becomes strongly coupled and flux flow behavior is evident. Series arrays of up to 20 junctions have been fabricated with sufficient parameter uniformity to achieve giant Shapiro steps under microwave radiation.
Physical Review B, 1991
%'e have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu307 z and... more %'e have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu307 z and evaporated metal counterelectrodes that exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3Q7 z, T" the conductance as a function of voltage, 6(V), has a linear dependence on voltage and some asymmetry. Below T"additional structure associated with the superconducting state appears in G(V). At T « T, there is a reproducible finite zero-bias conductance, which suggests that there are states at the Fermi energy in superconducting YBa2Cu3O7 &. Junctions with Pb, Sn, Bi, Sb, PbBi, and Au cnunterelectrodes all show qualitatively similar behavior.
Physical Review B, 1985
We report tunneling measurements on quench-condensed films of tin in order to determine the corre... more We report tunneling measurements on quench-condensed films of tin in order to determine the correction to the two-dimensional electronic density of states due to the effects of electron-electron interactions. Comparison with recent theory yields good agreement in the regime that the theories are valid. These measurements illustrate the nature of the corrections over a wider range of parameters.
Applied Physics Letters, 2015
Physical Review Letters, 1989
We have fabricated tunnel junctions between chemically etched single crystals of YBazCu307 and ev... more We have fabricated tunnel junctions between chemically etched single crystals of YBazCu307 and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu307, T" the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below T"additional structure associated with the superconductivity appears in G (V). At T« T, there is a reproducible, finite, zero-bias conductance which suggests that there are states at the Fermi energy in superconducting YBa2Cu307. Junctions with Pb, Sn, Bi, Sb, PbBi, and Au counterelectrodes all show qualitatively similar behavior.
Physical Review Letters, 2008
We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed be... more We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi 2 Sr 2 CaCu 2 O 8+δ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson IcRn product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local IcRn product and the local energy gap. \end{abstract} (Body) Remarkable scanning tunneling microscopy (STM) studies on the high-T C superconducting cuprate (HTSC), Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) reveal spectral and energy gap inhomogeneities (1, 2), periodic electronic structure in the superconducting (SC) state (3) and structure inside vortex cores (4) as well as in the "pseudogap" state at temperatures above Tc (5). In these experiments the energy gap Δ is taken to be half the energy separation between the quasiparticle (QP) coherence peaks as observed in dI/dV spectra. The appearance of Δ has also been observed at a
Physical Review Letters, 1983
Tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb"Si... more Tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb"Si& are reported. The authors observe the correlation gap A which varies with resistivity and have related this to the metal-insulator transition as observed in the conductivity. The samples were prepared by a process which allows precise control of the Nb concentration. The results as a function of voltage, temperature, and concentration are compared with current theoretical predictions.
Physical Review Letters, 1980
The time-dependent specific heat of amorphous Si02 has been measured between 0.1 and 1 K over the... more The time-dependent specific heat of amorphous Si02 has been measured between 0.1 and 1 K over the range-1 sec to 10 &sec. The decoupling of the roughly T-'dependent contribution to specific heat is observed in submillisecond time scales, in qualitative agreement with the predictions of the tunneling model. However, the excess T3-dependent specific heat is not decoupled on the time scales involved. PACS numbers: 65.40.Em, 61.40.Df, 66.70.+f The thermal and transport properties' of amorphous materials below 1 K have been rather suc
Physical Review Letters, 1997
We report systematic magnetotransport measurements on a series of in situ grown homogeneous amorp... more We report systematic magnetotransport measurements on a series of in situ grown homogeneous amorphous Pb wires. Corresponding to the broadening of the superconducting transitions as the wires cross over from 2D to 1D, we observe a negative magnetoresistance (MR) below the mean-field T c at low fields. Both the magnitude of the negative MR and the crossover field increase with decreasing T c and wire cross-sectional area. We speculate that these observations are the result of superfluid density fluctuations in sign as well as in magnitude along these wires close to the superconductor-insulator transition.
Physical Review, 1968
We have calculated the phonon-limited resistivity of a number of simple metals. Information about... more We have calculated the phonon-limited resistivity of a number of simple metals. Information about the lattice dynamics is taken from inelastic neutron scattering experiments. l'rom a Born-von KArman forceconstant 6t to the data, we compute the solid structure factor as a function of temperature using a onephonon approximation. This should be adequate for the relatively low temperatures considered in this work. The resistivity is given simply as a quadrature of the structure factor times the square of the electron-ion pseudopotential form factor, which we take to be of the Heine-Abarenkov form. Good agreement is obtained with experiment for both absolute value and detailed variation with temperature.
The current-voltage characteristics (I-V) of some metal-barrier Josephson junctions include a cur... more The current-voltage characteristics (I-V) of some metal-barrier Josephson junctions include a current component that does not exhibit the DC, or AC Josephson effects. This current is referred to as the excess current, I χ. Moreover, while I χ is negligible around the transition temperature T C , it increases and can exceed 50% of the total current as temperature is decreased. Normally, I χ is omitted from Josephson I-V models and this leads to a large overestimate of the product of Josephson critical current, I C , and normal-state resistance, R N (i.e., I C R N). We have developed an extended I-V model based on the Stewart-McCumber and Ambegaokar-Halperin models that includes I χ. Using our model, we fit experimental I-V data for planar Y-Ba-Cu-O junctions over a range of temperatures. From these fits we obtain values for I χ , I C and R N , as well as noise temperature. Our values agree well with experimental measurements. I C is suppressed using a magnetic field. Further, our I C exhibits an asymptotic temperature dependence like that expected for a superconducting energy gap well below T C. Our model is an improvement over existing models as it reliably estimates I C R N .
Surface Science, 1984
We report experiments on the propagation of ballistic phonons through the (001) inversion layer o... more We report experiments on the propagation of ballistic phonons through the (001) inversion layer of Si. An attenuation is observed which is an order of magnitude larger than can be accounted for by absorption alone. A new, dynamical phonon scattering theory is presented which provides an explanation.
Surface Science, 1982
Measurements of the absorption of ballistic phonons by the twodimensional electron gas (2DEG) in ... more Measurements of the absorption of ballistic phonons by the twodimensional electron gas (2DEG) in the inversion layer of a Si MOSFET are presented and compared with theory.
Physical Review Letters, 1992
The induced magnetization of an isotropic type-II superconductor with an anisotropic sample shape... more The induced magnetization of an isotropic type-II superconductor with an anisotropic sample shape has been measured in an oblique magnetic field and separated into its reversible and irreversible contributions. The measurements unexpectedly show that the irreversible magnetization is oriented essentially parallel to the smallest sample dimension, and is almost independent of the angle of the applied field. This behavior can be understood by considering the critical-state model when the applied field is at an arbitrary direction with respect to the sample axes.
IEEE Transactions on Magnetics, 1977
We have fabricated thin films of Nb3Ge, Nb3Sn, V3Si and V3Ge and investigated their superconducti... more We have fabricated thin films of Nb3Ge, Nb3Sn, V3Si and V3Ge and investigated their superconducting and structural properties. In the case of the Nb compounds the dependence of Tc, resistance ratio and phase on stoichiometry have been determined. Defects have also been introduced into these films, in a controlled fashion, by irradiation with 1.9 MeV4He particles, and the structural and
IEEE Transactions on Applied Superconductivity, 2013
The voltage as a function of applied magnetic field (V-B) was calculated for arrays of supercondu... more The voltage as a function of applied magnetic field (V-B) was calculated for arrays of superconducting quantum interference devices (SQUIDs) connected in series. Comparisons were made between arrays of equal area SQUIDs and superconducting quantum interference filters (SQIFs). The areas for the SQIFs were varied exponentially, so that the V-B had a sharp minimum at zero field. We used equations for the dc SQUID based on resistively shunted junctions, with typical parameters for YBa2Cu3O7 - δ ion damage Josephson junctions. The maximum transfer coefficient of the central minimum VB = (∂V/∂B)max of the SQIF decreases as the area range increases. We find that the equal area array is more robust to the effects of non-uniform junction critical currents than the SQIF, for the junction parameters and SQUID area distributions chosen. Furthermore, we find that slight variations (~5%) to the area due to fabrication irregularities have little effect on the central minimum of V-B for either device.
The "restless" trajectory of my career from physics undergraduate to university president follows... more The "restless" trajectory of my career from physics undergraduate to university president follows the nature of physics itself. In physics, you are constantly seeking challenges, experimenting, creating hypotheses, looking for and finding solutions. I recall having a structured view of the world as a boy, a sense that there was a guiding "master plan" to most things and that wise, educated, benevolent people were there to implement the plan. "They" would do the right thing. Along the way, I realized, "there is no 'they' there; there is only us." Acknowledging the laws of thermodynamics-"you can't win, you can't break even, and you can't get out of the game"-I nonetheless believe that if you have a restless mind, an open heart, and intellectual honesty without giving into wishful thinking, physicists can do anything. .
the years to come, the size and cost of cryo-coolers will get smaller and the demand for a VLSI J... more the years to come, the size and cost of cryo-coolers will get smaller and the demand for a VLSI Josephson junction technology will increase. One possible candidate to fill this need is the "ion-damage" Josephson junction. These junctions are fabricated by using ion bombardment to create localized narrow regions of defects in the plane of a thin film of superconductor. These regions have a superconducting transition temperature lower than that of the bulk film and act as hysteretic Josephson junctions. The advantage of these junctions over other technologies is that they have no interfaces between different materials, and can be placed over 10 times closer to each other in comparison to competing techniques. Individual junctions and series arrays were fabricated from YBCO and magnesium diboride. Junction current-voltage characteristics near the critical temperature follow the resistively shunted junction model however at lower temperatures the barrier becomes strongly coupled and flux flow behavior is evident. Series arrays of up to 20 junctions have been fabricated with sufficient parameter uniformity to achieve giant Shapiro steps under microwave radiation.
Physical Review B, 1991
%'e have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu307 z and... more %'e have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu307 z and evaporated metal counterelectrodes that exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3Q7 z, T" the conductance as a function of voltage, 6(V), has a linear dependence on voltage and some asymmetry. Below T"additional structure associated with the superconducting state appears in G(V). At T « T, there is a reproducible finite zero-bias conductance, which suggests that there are states at the Fermi energy in superconducting YBa2Cu3O7 &. Junctions with Pb, Sn, Bi, Sb, PbBi, and Au cnunterelectrodes all show qualitatively similar behavior.
Physical Review B, 1985
We report tunneling measurements on quench-condensed films of tin in order to determine the corre... more We report tunneling measurements on quench-condensed films of tin in order to determine the correction to the two-dimensional electronic density of states due to the effects of electron-electron interactions. Comparison with recent theory yields good agreement in the regime that the theories are valid. These measurements illustrate the nature of the corrections over a wider range of parameters.
Applied Physics Letters, 2015
Physical Review Letters, 1989
We have fabricated tunnel junctions between chemically etched single crystals of YBazCu307 and ev... more We have fabricated tunnel junctions between chemically etched single crystals of YBazCu307 and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu307, T" the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below T"additional structure associated with the superconductivity appears in G (V). At T« T, there is a reproducible, finite, zero-bias conductance which suggests that there are states at the Fermi energy in superconducting YBa2Cu307. Junctions with Pb, Sn, Bi, Sb, PbBi, and Au counterelectrodes all show qualitatively similar behavior.
Physical Review Letters, 2008
We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed be... more We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi 2 Sr 2 CaCu 2 O 8+δ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson IcRn product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local IcRn product and the local energy gap. \end{abstract} (Body) Remarkable scanning tunneling microscopy (STM) studies on the high-T C superconducting cuprate (HTSC), Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) reveal spectral and energy gap inhomogeneities (1, 2), periodic electronic structure in the superconducting (SC) state (3) and structure inside vortex cores (4) as well as in the "pseudogap" state at temperatures above Tc (5). In these experiments the energy gap Δ is taken to be half the energy separation between the quasiparticle (QP) coherence peaks as observed in dI/dV spectra. The appearance of Δ has also been observed at a
Physical Review Letters, 1983
Tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb"Si... more Tunneling and conductivity measurements through the metal-insulator transition in amorphous Nb"Si& are reported. The authors observe the correlation gap A which varies with resistivity and have related this to the metal-insulator transition as observed in the conductivity. The samples were prepared by a process which allows precise control of the Nb concentration. The results as a function of voltage, temperature, and concentration are compared with current theoretical predictions.
Physical Review Letters, 1980
The time-dependent specific heat of amorphous Si02 has been measured between 0.1 and 1 K over the... more The time-dependent specific heat of amorphous Si02 has been measured between 0.1 and 1 K over the range-1 sec to 10 &sec. The decoupling of the roughly T-'dependent contribution to specific heat is observed in submillisecond time scales, in qualitative agreement with the predictions of the tunneling model. However, the excess T3-dependent specific heat is not decoupled on the time scales involved. PACS numbers: 65.40.Em, 61.40.Df, 66.70.+f The thermal and transport properties' of amorphous materials below 1 K have been rather suc
Physical Review Letters, 1997
We report systematic magnetotransport measurements on a series of in situ grown homogeneous amorp... more We report systematic magnetotransport measurements on a series of in situ grown homogeneous amorphous Pb wires. Corresponding to the broadening of the superconducting transitions as the wires cross over from 2D to 1D, we observe a negative magnetoresistance (MR) below the mean-field T c at low fields. Both the magnitude of the negative MR and the crossover field increase with decreasing T c and wire cross-sectional area. We speculate that these observations are the result of superfluid density fluctuations in sign as well as in magnitude along these wires close to the superconductor-insulator transition.