Browsing by Author "Rosenstein, B."

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3D DIRAC SEMI-METAL IN THE TRIPLET SUPERCONDUCTING STATE
(2015-01-01)
Rosenstein, B.
;
Shapiro, B. Ya.
;
Shapiro, I.
;
交大名義發表
;
National Chiao Tung University
It was recently shown that conventional phonon-electron interactions may induce a triplet pairing state in time-reversal invariant 3D Dirac semi - metals. Starting from the microscopic model of the isotropic Dirac semi-metal, the Ginzburg-Landau equations for the vector order parameter is derived using the Gorkov technique. The time dependent Ginzburg - Landau model in the presence of external fields is used to investigate some optical and magnetic properties of such superconductors. The AC conductivity of a clean sample depends on the orientation of the order parameter. It is demonstrated that the difference between the penetration depths results in rotation of the polarization vector of microwave passing a slab made of this material. The upper critical magnetic field H-c2 was found. It turns out that at fields close to H-c2 the order parameter orients itself perpendicular to the field direction. In certain range of parameters the triplet superconducting phase persists at arbitrarily high magnetic field like in some p wave superconductors.
Ballistic transport in graphene beyond linear response
(2010-01-15)
Rosenstein, B.
;
Lewkowicz, M.
;
Kao, H. C.
;
Korniyenko, Y.
;
電子物理學系
The process of coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described beyond linear response. We calculate the evolution of current density, number of pairs and energy in ballistic regime for electric field E using the tight-binding model. While for ballistic flight times smaller than t(nl)proportional to E(-1/2) current is linear in E and independent of time, for larger ballistic times the current increases after t(nl) as J proportional to E(3/2)t and finally at yet larger times (t > t(B) proportional to E(-1)) Bloch oscillations set in. It is shown that the number of pairs follows the 2D generalization of the Schwinger's creation rate n proportional to E(3/2) only on certain time segments with a prefactor different from that obtained using the asymptotic formula.
Ballistic transport, chiral anomaly, and emergence of the neutral electron-hole plasma in graphene
(2010-07-07)
Kao, H. C.
;
Lewkowicz, M.
;
Rosenstein, B.
;
電子物理學系
;
Department of Electrophysics
The process of coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described using a dynamic "first-quantized" approach. We calculate the evolution of current density, number of pairs, and energy in ballistic regime using the tight-binding model. The series in electric field strength E up to third order in both dc and ac are calculated. We show how the physics far from the two Dirac points enters various physical quantities in linear response and how it is related to the chiral anomaly. The third harmonic generation and the imaginary part of conductivity are obtained. It is shown that at certain time scale t(nl) alpha E-1/2 the physical behavior dramatically changes and the perturbation theory breaks down. Beyond the linear-response physics is explored using an exact solution of the first-quantized equations. While for small electric fields the I-V curve is linear characterized by the universal minimal resistivity sigma=pi/2(e(2)/h), at t>t(nl) the conductivity grows fast. The copious pair creation (with rate E-3/2), analogous to Schwinger's electron-positron pair creation from vacuum in QED, leads to creation of the electron-hole plasma at ballistic times of order t(nl). This process is terminated by a relaxational recombination.
Chiral Anomaly and Strength of the Electron-Electron Interaction in Graphene
(2013-02-08)
Rosenstein, B.
;
Lewkowicz, M.
;
Maniv, T.
;
電子物理學系
;
Department of Electrophysics
The long-standing controversy concerning the effect of electron-electron interaction on the electrical conductivity of an ideal graphene sheet is settled. Performing the calculation directly in the tight binding approach without the usual prior reduction to the massless Dirac (Weyl) theory, it is found that, to leading order in the interaction strength alpha = e(2)/(h) over barv(0), the dc conductivity sigma/sigma(0) = 1 + C alpha + O(alpha(2)) is significantly enhanced with respect to the independent-electron result sigma(0), i.e., with the value C = 0.26. The ambiguity characterizing the various existing approaches is nontrivial and related to the chiral anomaly in the system. In order to separate the energy scales in a model with massless fermions, contributions from regions of the Brillouin zone away from the Dirac points have to be accounted for. Experimental consequences of the relatively strong interaction effect are briefly discussed. DOI: 10.1103/PhysRevLett.110.066602
Collective modes, ac response, and magnetic properties of the three-dimensional Dirac semimetal in the triplet superconducting state
(2015-08-03)
Rosenstein, B.
;
Shapiro, B. Ya.
;
Shapiro, I.
;
電子物理學系
;
Department of Electrophysics
It was recently shown that conventional phonon-electron interactions may induce a triplet pairing state in time-reversal invariant three-dimensional Dirac semimetals. Starting from the microscopic model of the isotropic Dirac semimetal, the Ginzburg-Landau equations for the vector order parameter is derived using the Gor'kov technique. The collective modes including gapless Goldstone modes and gapped Higgs modes of various polarizations are identified. They are somewhat analogous to the modes in the B phase of He-3, although in the present case quantitatively there is a pronounced difference between longitudinal and transverse components. The difference is caused by the vector nature of the order parameter leading to two different coherence lengths or penetration depths. The system is predicted to be highly dissipative due to the Goldstone modes. The time-dependent Ginzburg-Landau model in the presence of external fields is used to investigate some optical and magnetic properties of such superconductors. The ac conductivity of a clean sample depends on the orientation of the order parameter. It is demonstrated that the difference between the penetration depths results in rotation of the polarization vector of microwave passing a slab made of this material. The upper critical magnetic field H-c2 was found. It turns out that at fields close to H-c2 the order parameter orients itself perpendicular to the field direction. In certain range of parameters the triplet superconducting phase persists at arbitrarily high magnetic field like in some p-wave superconductors.
Covariant gaussian approximation in Ginzburg-Landau model
(2017-05-01)
Wang, J. F.
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Li, D. P.
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Kao, H. C.
;
Rosenstein, B.
;
電子物理學系
Condensed matter systems undergoing second order transition away from the critical fluctuation region are usually described sufficiently well by the mean field approximation. The critical fluctuation region, determined by the Ginzburg criterion, vertical bar T/T-c, 1 vertical bar << Gi, is narrow even in high T, superconductors and has universal features well captured by the renormalization group method. However recent experiments on magnetization, conductivity and Nernst effect suggest that fluctuations effects are large in a wider region both above and below T-c. In particular some "pseudogap" phenomena and strong renormalization of the mean field critical temperature T-mf can be interpreted as strong fluctuations effects that are nonperturbative (cannot be accounted for by "gaussian fluctuations"). The physics in a broader region therefore requires more accurate approach. Self consistent methods are generally "non-conserving" in the sense that the Ward identities are not obeyed. This is especially detrimental in the symmetry broken phase where, for example, Goldstone bosons become massive. Covariant gaussian approximation remedies these problems. The Green's functions obey all the Ward identities and describe the fluctuations much better. The results for the order parameter correlator and magnetic penetration depth of the Ginzburg-Landau model of superconductivity are compared with both Monte Carlo simulations and experiments in high T-c, cuprates. (C) 2017 Elsevier Inc. All rights reserved.
Critical current of superconducting YBa2Cu3O7-delta films with different in-plane orientations
(2007-06-01)
Lin, P. A.
;
Chi, C. C.
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Rosenstein, B.
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電子物理學系
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Department of Electrophysics
By using a pulsed-laser deposition (PLD) technique, we grow high quality YBa2Cu3O7-delta films on YSZ (Yt-stabilized Zr) substrates with 0-degree and 45-degree in-plane orientations at 810 degrees C and 690 degrees C respectively. Surprisingly, despite the large difference in growth temperature the qualities of the films are almost the same. To study the subtle differences between these two types of films, we measured both the temperature and magnetic field dependencies of the critical current. Although there is very little difference in their magnetic field dependence, there is a distinct temperature dependence, i.e. J(c)(1 - T/T-c) proportional to (1 - T/T-c)(5/4) for 0 degree in-plane orientation and proportional to (1 - T/T-c)(3/2) for 45 degree in-plane orientation at temperatures near T-c. We also studied the critical current densities with different fractions of mixed orientations, and found an empirical formula J(c) proportional to e(5 alpha) where alpha is the fraction of the majority domain.
Current carrying vortex crystals
(2012)
Rosenstein, B.
;
Shapiro, I.
;
Berco, D.
;
Shapiro, B. Ya
;
電子物理學系
Abrikosov vortices in a type-II superconducting film subjected to strong magnetic field B with periodic array of nanoholes of the density n(pin) form sometimes a vortex crystal, even when they are driven by a transport current. It is shown numerically that the crystal melting and transition to the resistive state occurs as a coherent depinning of the single vortex dislocations. For a system with interstitial vortices, f = B/Phi(0)n(pin) > 1, the mechanism of depinning depends on the current direction with respect to the pinning array. It was found that slightly above the critical current trajectories of moving vortices are not straight, but rather acquire a snake - like shape enveloping the system of pins. In contrast to the matching field case, f = 1, the transition to a resistive state is not coherent and is developing through formation of the "snake - like" vortex trajectories. It is pointed out that the depinning is closely associated with the appearance of a strongly varying electric field. We calculated the electric fields accompanying vortex crystal melting and found the voltage-current characteristics. When the pinning array is made random, the critical current is reduced.
Dynamical approach to ballistic transport in graphene
(2011-01-01)
Kao, H. C.
;
Lewkowicz, M.
;
Korniyenko, Y.
;
Rosenstein, B.
;
電子物理學系
The process of the coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described beyond linear response We calculate the evolution of the current density and the number of pairs in the ballistic regime using the tight binding model While for small electric fields the I-V curve is linear characterized by the universal minimal resistivity sigma = pi/2(e(2)/h) for larger fields after a certain time interval the linear regime crosses over to a quadratic one and finally at larger times Bloch oscillations set in (C) 2010 Elsevier BV All rights reserved
Dynamics of disordered type-II superconductors: Peak effect and the I-V curves
(2007-09-01)
Bel, G.
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Li, D. P.
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Rosenstein, B.
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Vinokur, V.
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Zhuravlev, V.
We quantitatively describe the competition between the thermal fluctuations and disorder by the Ginzburg-Landau approach using both the replica method in statics and the dynamical Martin-Siggia-Rose approach which allows generalization beyond linear response. The two methods are consistent in static, while the dynamical method allows calculation of the critical current as function of magnetic field and temperature. The surface in the J-B-T space defined by this function separates between a dissipative moving vortex matter regime and vortex glass. The non-Ohmic I-V curve is obtained. (c) 2007 Elsevier B.V. All rights reserved.
Dynamics of electric transport in interacting Weyl semimetals
(2013-07-03)
Rosenstein, B.
;
Lewkowicz, M.
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電子物理學系
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Department of Electrophysics
The response to an electric field (dc and ac) of electronic systems in which the Fermi "surface" consists of a number of three-dimensional (3D) Weyl points (such as some pyrochlore iridates) exhibits a peculiar combination of characteristics usually associated with insulating and conducting behavior. Generically a neutral plasma in clean materials can be described by a tight-binding model with a strong spin-orbit interaction. A system of that type has a vanishing dc conductivity; however the current response to the dc field is very slow: The current decays with time in a powerwise manner, different from an insulator. The ac conductivity, in addition to a finite real part sigma'(Omega) which is linear in frequency, exhibits an imaginary part sigma '' (Omega) that increases logarithmically as a function of the UV cutoff (atomic scale). This leads to a substantial dielectric response like a large dielectric constant at low frequencies. This is in contrast to a two-dimensional (2D) Weyl semimetal-like graphene at a neutrality point where the ac conductivity is purely pseudodissipative. The Coulomb interaction between electrons is long range and sufficiently strong to make a significant impact on transport. The interaction contribution to the ac conductivity is calculated within the tight-binding model. The result for the real part expressed via the renormalized (at frequency (Omega) over bar) Fermi velocity nu is Delta sigma'(Omega) = e(4)Omega/(9 pi(2)(h) over bar nu)[2 log(Omega/ (Omega) over bar)-5].
Dynamics of Particle-Hole Pair Creation in Graphene
(2009-03-13)
Lewkowicz, M.
;
Rosenstein, B.
;
電子物理學系
;
Department of Electrophysics
The process of coherent creation of particle-hole excitations by an electric field in graphene is quantitatively described. We calculate the evolution of the current density, number of pairs, and energy after switching on the electric field. In particular, it leads to a dynamical visualization of universal finite resistivity without dissipation in pure graphene. We show that the dc conductivity of pure graphene is pi/2e(2)/h rather than the often cited value of 4/pi e(2)/h. This value coincides with the ac conductivity calculated and measured recently at optical frequencies. The effect of temperature and random chemical potential (charge puddles) are considered and explain the recent experiment on suspended graphene. A possibility of Bloch oscillations is discussed within the tight binding model.
Effect of nanoholes on the vortex core fermion spectrum and heat transport in p-wave superconductors
(2013-02-20)
Rosenstein, B.
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Shapiro, I.
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Shapiro, B. Ya
;
電子物理學系
;
Department of Electrophysics
The spectrum of core excitations of the Abrikosov vortex pinned by a nanohole of the size of the coherence length is considered. While the neutral zero energy Majorana core state remains intact due to its topological origin, the energy of charged excitations is significantly enhanced compared to that in the unpinned vortex. As a consequence of the pinning the minigap separating the Majorana state from the charged levels increases from Delta(2)/E-F (E-F is the Fermi energy and Delta is the bulk p-wave superconducting gap) to a significant fraction of Delta. Suppression of the thermodynamic and kinetic effects of the charged excitations allows us to isolate the Majorana state so it can be used for quantum computation. It is proposed that thermal conductivity along the vortex cores is a sensitive method to demonstrate the minigap. Using the Butticker-Landauer-Kopnin formula, we calculate the thermal conductance beyond the linear response as a function of the hole radius.
Elastic properties of the Abrikosov lattice near the upper critical field and peak effect in the critical current
(2008-02-15)
Rosenstein, B.
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Zhuravlev, V.
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電子物理學系
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Department of Electrophysics
Abrikosov vortices in type II superconductors under magnetic field form highly correlated configurations with well defined elasticity, like regular atomic solids. While in the London limit vortices can be considered as line-like objects, when the field approaches the upper critical field H-c2(T) the core structure becomes important for elastic properties. Taking into account the deformation of the shape of the current distribution leads to significant increase in the shear modulus of the vortex lattice compared to previous estimates. The elastic properties determine the response to vortex matter pinning. The modified value of the elastic modulus is used to support a recent theory of the discontinuous "peak effect" in the critical current. It is argued that the critical current of the vortex lattice decreases monotonously as a function of the magnetic field, jumping to a high value in the homogeneous amorphous phase. (c) 2007 Published by Elsevier B.V.
Electrodynamics of type-II superconductor with periodic pinning array
(2011-01-01)
Hung, R. F.
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Berco, D.
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Shapiro, I. Ya
;
Shapiro, B.
;
Rosenstein, B.
Static and dynamic distribution of the superconducting condensate order parameters and current density is studied by numerical simulation of the 2D time-dependent Ginzburg-Landau equations The vortex flux lattice in layered type-II superconductors under magnetic field above the lower critical field is described by the order parameters Moreover the pinning effect has been considered in this work The Abrikosov lattice which is hexagonal in the static case is deformed due to the size of pinning centers The dynamical order parameters distribution shows that the vortex transport (flux flow) is conducted via diffusive motion of the so-called interstitial vortices The trajectories for interstitial vortices with different sizes of pinning centers are shown (C) 2010 Elsevier BV All rights reserved
Exchange Interaction Makes Superconductivity in 3D Dirac Semi-metal Triplet
(2015-04-01)
Rosenstein, B.
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Shapiro, B. Ya
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Li, Dingping
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Shapiro, I.
;
電子物理學系
Conventional electron-phonon coupling induces either odd (triplet) or even (singlet) pairing states in a time reversal and inversion invariant Dirac semi-metal. In a certain range of the chemical potential and parameters characterizing the pairing attraction (effective electron-electron coupling constant and the Debye energy ) the energy of the singlet although always lower, prevails by a very slim margin over the triplet. This means that interactions that are small but discriminate between the spin singlet and the spin triplet determine the nature of the superconducting order there. It is shown that in materials close enough to the Dirac point ( ) a moderate exchange constant (below Stoner instability to ferromagnetism) stabilizes the odd pairing superconducting state. The 3D quantum critical point at of transition to the triplet superconductivity governs the physics of the superconductor.
Experimental Presentation of Microwave Absorption due to Shaking of JV by AC Magnetic Field in Bi2212 and Bi2223
(2009-05-01)
Shaltiel, D.
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von Nidda, H. -A. Krug
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Shapiro, B. Y.
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Rosenstein, B.
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Loidl, A.
The Josephson Vortex dynamics in high anisotropy superconductors Bi2212 and Bi2223 induced by AC magnetic field collinear to DC magnetic field and parallel to the layers is studied via their interaction with microwave field. Experimental results as function of DC magnetic field, AC magnetic field and temperature are presented. The AC induced microwave dissipation is larger than dissipation without AC field. The results are explained by the theoretical interpretation reported recently due to shaking by the AC field that depins the JV (Shaltiel et al., Phys. Rev. B 77, 014508, 2008). Similar behavior in these two compounds as a function of the variables involved discloses that the shaking effect should be observed in any high anisotropy superconductors. It shows that the AC field interacting with JV has an active and not the usual passive modulating role of the DC field in EPR dissipation experiments. The technique can be used to investigate JV dynamics and JV phase diagram.
Extended object tunneling: Current-carrying states of Abrikosov vortices in a superconductor with artificial nanobarriers
(2012-02-24)
Rosenstein, B.
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Shapiro, I.
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Shapiro, B. Ya.
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Li, Dingping
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Frydman, A.
We consider the structure and dynamics of two-dimensional fluxons created by a magnetic field in a type-II superconductor film with critical temperature T-1 in the presence of nanostripes of material with a higher critical temperature T-2. The width of the stripes is of the order of the coherence length xi. Such a stripe plays the role of a potential barrier for vortices. When subjected to the current J parallel to the stripe, vortices move toward the barrier. Below the critical current J(c), the flux flow is effectively halted by the barrier, while above J(c), flux penetrates the stripe and passes the barrier. The mechanism of the barrier penetration ("soliton tunneling" occurs even at zero temperature) is rather unusual: the vortices adjust their shape, and upon passing the barrier, they shrink their cores. The critical current and the I-V curves are calculated numerically and analytically using variational approach.
Field cooling memory effect in Bi2212 and Bi2223 single crystals
(2010-07-01)
Shaltiel, D.
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von Nidda, H-A Krug
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Rosenstein, B.
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Shapiro, B. Ya
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Golosovsky, M.
A memory effect in the Josephson vortex system created by a magnetic field in the highly anisotropic superconductors Bi2212 and Bi2223 is demonstrated using microwave power absorption. This surprising effect appears despite a very low viscosity of Josephson vortices compared to Abrikosov vortices. The superconductor is field-cooled in a DC magnetic field H(m) oriented parallel to the CuO planes through the critical temperature T(c) down to 4 K, with subsequent reduction of the field to zero and again above H(m). A large microwave power absorption signal is observed at a magnetic field just above the cooling field, clearly indicating a memory effect. The dependence of the signal on a deviation of the magnetic field from H(m) is the same for a wide range of H(m) from 1500 to 17 000 G.
Glass transition and the replica symmetry breaking in vortex matter: MC study
(2011-01-01)
Li, Dingping
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Rosenstein, B.
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Chen, Shou
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Lin, H. H.
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Berco, D.
We investigate effects of disorder and thermal fluctuations on the Abrikosov state of type II superconductors applying the Monte Carlo method to Ginzburg-Landau theory to confirm earlier replica calculation The vortex phase diagram has two transition lines the melting line and the vortex glass transition lines in both crystalline and homogeneous states The glass line is always a continuous transition while the melting line is the first order (C) 2010 Elsevier BV All rights reserved