arXiv subjects

Igor Zutic

Publications and source records attributed to Igor Zutic.

86 records · Page 5Linked to original sources

arXiv2000

Issues, Concepts, and Challenges in Spintronics

We review from a theoretical perspective the emerging field of spintronics where active control of spin transport and dynamics in electronic materials may provide novel device application possibilities. In particular, we discuss the quantum mechanical principles underlying spintronics applications, emphasizing the formidable challenges involving spin decoherence and spin injection facing any eventual device fabrication. We provide a critical assessment of the current status of the field with special attention to possible device applications.

cond-mat↗

arXiv2000

Interface charged impurity scattering in semiconductor MOSFETs and MODFETs: temperature dependent resistivity and 2D "metallic" behavior

We present the results on the anomalous 2D transport behavior by employing Drude-Boltzmann transport theory and taking into account the realistic charge impurity scattering effects. Our results show quantitative agreement with the existing experimental data in several different systems and address the origin of the strong and non-monotonic temperature dependent resistivity.

cond-mat.str-el↗

arXiv2000

Spintronics: electron spin coherence, entanglement, and transport

Prospect of building spintronic devices in which electron spins store and transport information has attracted strong attention in recent years. Here we present some of our representative theoretical results on three fundamental aspects of spintronics: spin coherence, spin entanglement, and spin transport. In particular, we discuss our detailed quantitative theory for spin relaxation and coherence in electronic materials, resolving in the process a long-standing puzzle of why spin relaxation is extremely fast in Al (compared with other simple metals). In the study of spin entanglement, we consider two electrons in a coupled GaAs double-quantum-dot structure and explore the Hilbert space of the double dot. The specific goal is to critically assess the quantitative aspects of the proposed spin-based quantum dot quantum computer architecture. Furthermore, we discuss our theory of spin-polarized transport across a semiconductor-metal interface. In particular, we study Andreev reflection, which enables us to quantify the degree of carrier spin polarization and the strength of interfacial scattering.

cond-mat.mes-hall↗

arXiv2000

Theoretical Perspectives on Spintronics and Spin-Polarized Transport

Selected problems of fundamental importance for spintronics and spin-polarized transport are reviewed, some of them with a special emphasis on their applications in quantum computing and coherent control of quantum dynamics. The role of the solid-state environment in the decoherence of electron spins is discussed. In particular, the limiting effect of the spin-orbit interaction on spin relaxation of conduction electrons is carefully examined in the light of recent theoretical and experimental progress. Most of the proposed spintronic devices involve spin-polarized transport across interfaces in various hybrid structures. The specific example discussed here, of a magnetic semiconductor/superconductor interface, displays many intricacies which a complex spin-dependent interface introduces in the spin-polarized transport. It is proposed that pairs of entangled electrons in a superconductor (Cooper pairs) can be transfered to a non-superconducting region, and consequently separated for a transport study of the spin entanglement. Several important theoretical proposals for quantum computing are based on electronic and nuclear spin entanglement in a solid. Physical requirements for these proposals to be useful are discussed and some alternative views are presented. Finally, a recent discovery of optical control of nuclear spins in semiconductors is reviewed and placed in the context of a long-standing search for electronic control of nuclear dynamics.

cond-mat.mes-hall↗

arXiv1999

Spin-polarized transport and Andreev reflection in semiconductor/superconductor hybrid structures

We show that spin-polarized electron transmission across semiconductor/superconductor (Sm/S) hybrid structures depends sensitively on the degree of spin polarization as well as the strengths of potential and spin-flip scattering at the interface. We demonstrate that increasing the Fermi velocity mismatch in the Sm and S regions can lead to enhanced junction transparency in the presence of spin polarization. We find that the Andreev reflection amplitude at the superconducting gap energy is a robust measure of the spin polarization magnitude, being independent of the strengths of potential and spin-flip scattering and the Fermi velocity of the superconductor.

cond-mat.mes-hall↗

arXiv1999

Tunneling spectroscopy for ferromagnet/superconductor junctions

In tunneling spectroscopy studies of ferromagnet/superconductor (F/S) junctions, the effects of spin polarization, Fermi wavevector mismatch (FWM) between the F and S regions, and interfacial resistance play a crucial role. We study the low bias conductance spectrum of these junctions, governed by Andreev reflection at the F/S interface. We consider both d- and s-wave superconductors as well as mixed states of the $d+is$ form. We present results for a range of values of the relevant parameters and find that a rich variety of features appears, depending on pairing state and other conditions. We show that in the presence of FWM, spin polarization can enhance Andreev reflection and give rise to a zero bias conductance peak for an s-wave superconductor.

cond-mat.supr-con↗

arXiv1998

Spin polarized tunneling in ferromagnet/unconventional superconductor junctions

We study tunneling in ferromagnet/unconventional superconductor (F/S) junctions. We include the effects of spin polarization, interfacial resistance, and Fermi wavevector mismatch (FWM) between the F and S regions. Andreev reflection (AR) at the F/S interface, governing tunneling at low bias voltage, is strongly modified by these parameters. The conductance exhibits a very wide variety of features as a function of applied voltage.

cond-mat.supr-con↗

arXiv1998

Comment on "Is the nonlinear Meissner effect unobservable?"

In a recent Letter (Phys. Rev. Lett. 81, p.5640 (1998), cond-mat/9808249 v3), it was suggested that nonlocal effects may prevent observation of the nonlinear Meissner effect in YBCO. We argue that this claim is incorrect with regards to measurements of the nonlinear transverse magnetic moment, and that the most likely reason for a null result lies elsewhere.

cond-mat.supr-con↗

arXiv1998

Angular Dependence of the Nonlinear Transverse Magnetic Moment of YBCO in the Meissner state

The angular dependence of the nonlinear transverse magnetic moment of untwinned high-quality single crystals of optimally doped YBCO have been studied at a temperature of 2.5K using a low frequency AC technique. The absence of any signature at angular period 2π/4is analyzed in light of the numerical predictions of such a signal for a pure d-wave order parameter with line nodes. Implications of this null result for the existence of a non-zero gap at all angles on the Fermi surface are discussed.

cond-mat.supr-con↗

arXiv1998

Low Frequency Nonlinear Magnetic Response of an Unconventional Superconductor

We consider an unconventional superconductor in a low frequency harmonic magnetic field. In the Meissner regime at low T a nonlinear magnetic response arises from quasiparticle excitations near minima in the energy gap. Various physical quantities then acquire higher harmonics of the frequency of the applied field. We discuss how examination of the field and angular dependence of these harmonics allows determination of the structure of the energy gap. We show how to distinguish nodes from small finite minima ("quasinodes"). Gaps with nodal lines give rise to universal power law field dependences for the nonlinear magnetic moment and the nonlinear torque. They both have separable temporal and angular dependences. In contrast, when there are quasinodes these quantities have more complicated and nonseparable field, temporal, and angular dependences. We illustrate this on the example of an s+id gap. We discuss how to perform measurements so as to maximize the nonlinear signal and how to investigate in detail the properties of the superconducting minima, thus determining the gap function symmetry.

cond-mat.supr-con↗

arXiv1997

Computation of the Nonlinear Magnetic Response of a Three Dimensional Anisotropic Superconductor

Many problems in computational magnetics involve computation of fields which decay within a skin depth $δ$, much smaller than the sample size $d$. We discuss here a novel perturbation method which exploits the smallness of $ε\equiv δ/ d$ and the asymptotic behavior of the solution in the exterior and interior of a sample. To illustrate this procedure we consider the computation of the magnetic dipole and quadrupole moments of an anisotropic, unconventional, three dimensional superconductor. The method significantly reduces the required numerical work and can be implemented in different numerical algorithms.

cond-mat.supr-con↗

arXiv1997

Superconducting gap node spectroscopy using nonlinear electrodynamics

We present a method to determine the nodal structure of the energy gap of unconventional superconductors such as high $T_c$ materials. We show how nonlinear electrodynamics phenomena in the Meissner regime, arising from the presence of lines on the Fermi surface where the superconducting energy gap is very small or zero, can be used to perform ``node spectroscopy'', that is, as a sensitive bulk probe to locate the angular position of those lines. In calculating the nonlinear supercurrent response, we include the effects of orthorhombic distortion and $a-b$ plane anisotropy. Analytic results presented demonstrate a systematic way to experimentally distinguish order parameters of different symmetries, including cases with mixed symmetry (for example, $d+s$ and $s+id$). We consider, as suggested by various experiments, order parameters with predominantly $d$-wave character, and describe how to determine the possible presence of other symmetries. The nonlinear magnetic moment displays a distinct behavior if nodes in the gap are absent but regions with small, finite, values of the energy gap exist.

cond-mat.supr-con↗

arXiv1997

Numerically implemented perturbation method for the nonlinear magnetic moment of an anisotropic superconductor

We present a method to compute the magnetic moment of a bulk, finite-size, three-dimensional, anisotropic superconductor. Our numerically implemented perturbative procedure is based on a solution of the nonlinear Maxwell- London equations, where we include the nonlinear relation between current and gauge invariant velocity. The method exploits the small ratio of penetration depth to sample size. We show how to treat the open boundary conditions over an infinite domain and the continuity requirement at the interface. We demonstrate how our method substantially reduces the computational work required and discuss its implementation to an oblate spheroid. The numerical solution is obtained from a finite difference method. We briefly discuss the relevance of this work to similar problems in other fields.

cond-mat.supr-con↗

arXiv1996

Nonlinear transverse magnetic moment in anisotropic superconductors

We consider the nonlinear transverse magnetic moment that arises in the Meissner state of superconductors with strongly anisotropic order parameter. We compute this magnetic moment as a function of applied field and geometry, assuming d-wave pairing, for realistic samples, finite in all three dimensions, of high temperature superconducting materials. Return currents, shape effects and the anisotropy of the penetration depth are all included. We numerically solve the nonlinear Maxwell-London equations for a finite system. The effect, which is a probe of the order parameter symmetry in the bulk of the sample, should be readily measurable if pairing is in a d-wave state. Failure to observe it would set a lower bound to the s-wave component.

cond-mat↗