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The latent heat of vortex lattice melting transition in a two-dimensional superconductor at high perpendicular magnetic field is calculated within the framework of the Ginzburg-Landau functional integral approach. The result is found to be smaller than that obtained from various numerical simulations, which tend to overestimate the latent heat due to finite-size effect.

We present the results of a systematic study of thin-films of amorphous indium-oxide near the superconductor-insulator transition. We show that the film's resistivity follows a simple, well-defined, power-law dependence on the perpendicular magnetic field. This dependence holds well into the insulating state. Our results indicate that vortices play a central role in the transport of our films in the superconducting as well as insulating phases., Comment: Final accepted version; 11 pages with 5 embedded figures

The object of the present work is to study the quantum Hall effect through its symmetries and topological aspects. We consider the model of an electron moving in a two-dimensional lattice in the presence of applied in-plain electric field and perpendicular magnetic field. We refer to this as the two dimensional electric-magnetic Bloch problem (EMB). The Hall conductivity quatizations beyond the linear response approximation is analyzed., Comment: 6 pages

The Hall-resistance curve of a two-dimensional electron system in the presence of a strong perpendicular magnetic field is an example of self-similarity. It reveals plateaus at low temperatures and has a fractal structure. We show that this fractal structure emerges naturally in the Hamiltonian formulation of composite fermions. After a set of transformations on the electronic model, we show that the model, which describes interacting composite fermions in a partially filled energy level, is self-similar. This mathematical property allows for the construction of a basis of higher generations of composite fermions. The collective-excitation dispersion of the recently observed 4/11 fractional-quantum-Hall state is discussed within the present formalism., Comment: 7 pages, 4 figures; version accepted for publication in Europhys. Lett., new version contains energy calculations for collective excitations of the 4/11 state

We show that small structures can be defined in high mobility two‐dimensional electron gases formed at a depth of 2770 A below the surface in GaAs/Al0.33Ga0.67As heterostructures. The differential conductance of one‐dimensional constrictions defined by split gates in such deep electron gases showed more than 20 quantised plateaus. The absence of resonant structures on the plateaus demonstrates the absence of potential fluctuations in the constrictions. By applying a dc source‐drain bias we have measured the energy spacings of the first 18 subbands, and the effect of a small perpendicular magnetic field on the energy spacings has been investigated.

We have numerically investigated the dynamics of vortices in a clean layered superconductor placed in a perpendicular magnetic field. We describe the energetics using a Ginzburg-Landau free energy functional in the lowest Landau level approximation. The dynamics are determined using the time-dependent Ginzburg-Landau approximation, and thermal fluctuations are incorporated via a Langevin term. The c-axis conductivity at nonzero frequencies, as calculated from the Kubo formalism, shows a strong but not divergent increase as the melting temperature $T_M$ is approached from above, followed by an apparently discontinuous drop at the vortex lattice freezing temperature. The discontinuity is consistent with the occurrence of a first-order freezing. The calculated equilibrium properties agree with previous Monte Carlo studies using the same Hamiltonian. We briefly discuss the possibility of detecting this fluctuation conductivity experimentally., Comment: To be published in Phys. Rev. B

The activation gap $\Delta$ of the fractional quantum Hall states at constant fillings $\nu =2/3$ and 2/5 has been measured as a function of the perpendicular magnetic field $B$. A linear dependence of $\Delta$ on $B$ is observed while approaching the spin polarization transition. This feature allows a direct measurement of the $g$-factor of composite fermions which appears to be heavily renormalized by interactions and strongly sensitive to the electronic filling factor., Comment: 4 pages, 4 figures Changed content: Fokus more on g-factors (and less on other details)

Analytical investigations of the critical state are carried out for a superconducting stripline consisting of two individual coplanar strips with an arbitrary distance between them. Two different cases are considered: a stripline with transport current and strips exposed to a perpendicular magnetic field. In the second case, the obtained solutions correspond to "fieldlike" (for unclosed strips) and "currentlike" (for a long rectangular superconducting loop) states in an isolated strip to which both a transport current and a magnetic field are applied with constant ratio., Comment: 8 pages, 6 figures. accepted by SST

Shielding materials have traditionally been measured using plane waves. For a significant number of applications, measurement using a perpendicular magnetic field is more appropriate. This paper reports on a method of characterizing shielding materials using a perpendicular magnetic field. Many properties of shielding materials can be easily determined by this method which is especially suited for coated or loaded plastics. Results for several commonly available shielding materials are presented and compared to plane wave, far field measurements. >

We have studied the electronic properties and optical absorption spectra of three different cases of donor centers, D^{0}, D^{-} and D^{2-}, which are subjected to a perpendicular magnetic field, using the exact diagonalization method. The energies of the lowest lying states are obtained as function of the applied magnetic field strength B and the distance zeta between the positive ion and the confinement xy-plane. Our calculations indicate that the positive ion induces transitions in the ground-state, which can be observed clearly in the absorption spectra, but as zeta goes to 0 the strength of the applied magnetic field needed for a transition to occur tends to infinity., 5 pages, 4 figures, REVTeX 4, gzipped tar file

It was recently observed [van der Beek et al., Phys. Rev. B 54, R792 (1996)] that irradiated layered high-T c superconductors subject to perpendicular magnetic field manifest two similar scaling behaviors corresponding totwo different critical temperatures. We show that this phenomenon is explained within the framework of the Ginzburg-Landau theory, In the weak field region, the scaling function differs from that of a clean sample mainly because of the renormalization of the critical temperature, due to defects. In the strong field region, defects are effectively suppressed and the scaling function, as well as the critical temperature, are the same as in a clean superconductor. The theory presented here agrees quite satisfactory with experiment.

We consider the effects of a perpendicular magnetic field on the d-density wave order and conclude that if the pseudogap phase in the cuprates is due to this order, then it is highly insensitive to the magnetic field in the underdoped regime, while its sensitivity increases as the gap vanishes in the overdoped regime. This appears to be consistent with the available experiments and can be tested further in neutron scattering experiments. We also investigate the nature of the de Haas- van Alphen effect in the ordered state and discuss the possibility of observing it., 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo in the abstract

We study tunneling between two nearby cleaved edge quantum wires in a perpendicular magnetic field. Due to Coulomb forces between electrons, the wires form a strongly-interacting pair of Luttinger liquids. We calculate the low-temperature differential tunneling conductance, in which singular features map out the dispersion relations of the fractionalized quasiparticles of the system. The velocities of several such spin-charge separated excitations can be explicitly observed. Moreover, the proposed measurement directly demonstrates the splintering of the tunneling electrons into a multi-particle continuum of these quasiparticles, carrying separately charge from spin. A variety of corrections to the simple Luttinger model are also discussed., Comment: 4 pages, 5 figures (1 in color)

Current-voltage (I-V) characteristics of quench condensed, superconducting, ultrathin Bi films in a magnetic field are reported. These show hysteresis for all films, grown both with and without thin Ge underlayers. Films on Ge underlayers, close to superconductor-insulator transition, show a peak in the critical current, indicating a structural transformation of the vortex solid. These underlayers, used to make the films more homogeneous, are found to be more effective in pinning the vortices. The upper critical fields ($B_{c2}$) of these films are determined from the resistive transitions in perpendicular magnetic field. The temperature dependence of the upper critical field is found to differ significantly from Ginzburg-Landau theory, after modifications for disorder., Comment: Submitted to LT23 Proceedings

The sensitivity to temperature of the threshold current in a strained quantum-well semiconductor laser under a perpendicular magnetic field is determined quantitatively by means of a suitable merit parameter. The values taken on by this parameter are discussed in terms of changes in the temperature and in the magnetic-field strength.

A new gauge suitable for investigation of two-dimensional quantum wires in a perpendicular magnetic field is proposed.

We calculate the current distribution present in superconducting planar thin films of different geometries including strips with slits, -turns, and widenings. We consider simultaneous application of external transport electric current and perpendicular magnetic field and systematically obtain the current distribution. From the calculations we show how, based on different sequences of the externally applied magnitudes, one can control the current distribution in the thin sample.

Purpose: : To investigate dosimetric differences between MRI- and CT-based IMRT planning for prostate cancer, the impact of a magnetic field in a MRI-Linac, and to explore the feasibility of IMRT planning based on MRI alone. Methods: IMRT plans were generated based on CT and MRI images acquired on two representative prostate-cancer patients using clinical dose volume constraints. A research planning system (Monaco, Elekta), which employs a Monte Carlo dose engine and includes a perpendicular magnetic field of 1.5T from an MRI-Linac, was used. Bulk electron density assignments based on organ-specific values from ICRU 46 were used to convert MRI (T2) to pseudo CT. With the same beam configuration as in the original CT plan, 5 additional plans were generated based on CT or MRI, with or without optimization (i.e., just recalculation) and with or without the magnetic field. The plan quality in terms of commonly used dose volume (DV) parameters for all plans was compared. The statistical uncertainty on dose was < 1%. Results: For plans with the same contour set but without re-optimization, the DV parameters were different from those for the original CT plan, mostly less than 5% with a few exceptions. These differences were reduced to mostly less than 3% when the plans were re-optimized. For plans with contours from MRI, the differences in the DV parameters varied depending on the difference in the contours as compared to CT. For the optimized plans with contours from MR, the differences for PTV were less than 3%. Conclusion: The prostate IMRT plans based on MRI-only for a MR-Linac were practically similar as compared to the CT plan under the same beam and optimization configuration if the difference on the structure delineation is excluded, indicating the feasibility of using MRI-only for prostate IMRT.

Purpose: With the increasing use of MRI simulation and the advent of MRI-guided delivery, it is desirable to use MRI only for treatment planning. In this study, we assess the dosimetric difference between MRI- and CTbased IMRT planning for pancreatic cancer. Methods: Planning CTs and MRIs acquired for a representative pancreatic cancer patient were used. MRI-based planning utilized forced relative electron density (rED) assignment of organ specific values from IRCU report 46, where rED = 1.029 for PTV and a rED = 1.036 for non-specified tissue (NST). Six IMRT plans were generated with clinical dose-volume (DV) constraints using a research Monaco planning system employing Monte Carlo dose calculation with optional perpendicular magnetic field (MF) of 1.5T. The following five plans were generated and compared with the planning CT: 1.) CT plan with MF and dose recalculation without optimization; 2.) MRI (T2) plan with target and OARs redrawn based on MRI, forced rED, no MF, and recalculation without optimization; 3.) Similar as in 2 but with MF; 4.) MRI plan with MF but without optimization; and 5.) Similar as in 4 but with optimization. Results: Generally, noticeable differences in PTV point doses and DV parameters (DVPs) between the CT-and MRI-based plans with and without the MF were observed. These differences between the optimized plans were generally small, mostly within 2%. Larger differences were observed in point doses and mean doses for certain OARs between the CT and MRI plan, mostly due to differences between image acquisition times. Conclusion: MRI only based IMRT planning for pancreatic cancer is feasible. The differences observed between the optimized CT and MRI plans with or without the MF were practically negligible if excluding the differences between MRI and CT defined structures.

In non-interacting or weakly-interacting 2D electron systems, the energy of the extended states increases as the perpendicular magnetic field approaches zero: the extended states "float up" in energy, giving rise to an insulator. However, in those 2D systems where metallic conductivity has been recently observed in zero magnetic field, the energy of the extended states remains constant or even decreases as B -> 0, thus allowing conduction in the limit of zero temperature. Here we show that aligning the electrons' spins causes the extended states to once more "float up" in energy in the vanishing perpendicular magnetic field, as they do for non- or weakly-interacting electrons. The difference between extended states that float up (an insulator) or remain finite (a metal) is thus tied to the existence of the spins.

The intervortex interaction is investigated in very anisotropic layered superconductors in tilted magnetic field. In such a case, the crossing lattice of Abrikosov vortices (AVs) and Josephson vortices (JVs) appears. The interaction between pancakes vortices (PVs), forming the AVs, and JVs produces the deformation of the AV line. It is demonstrated that in the result of this deformation a long range attraction between AVs is induced. This phenomenon is responsible for the dense vortex chains formation. The vortex structure in weak perpendicular magnetic field is the vortex chain phase, while in higher field a more complicated mixed vortex chain-vortex lattice phase emerges., 4 Pages, 3 figures. submitted to PRL

We demonstrate the emergence of the quantum Hall (QH) hierarchy in a 2D model of coupled quantum wires in a perpendicular magnetic field. At commensurate values of the magnetic field, the system can develop instabilities to appropriate inter-wire electron hopping processes that drive the system into a variety of QH states. Some of the QH states are not included in the Haldane-Halperin hierarchy. In addition, we find operators allowed at any field that lead to novel crystals of Laughlin quasiparticles. We demonstrate that any QH state is the groundstate of a Hamiltonian that we explicitly construct., Revtex, 4 pages, 2 figures

The transition from the quantum Hall state to the insulator is considered for non-interacting electrons in a two-dimensional disordered lattice model with perpendicular magnetic field. Using correlated random disorder potentials the floating up of the critical states can be observed in a similar way as in the continuum model. Thus, the peculiar behaviour of the lattice models reported previously originates in the special choice of uncorrelated random disorder potentials., Comment: 4 pages incl. 4 eps-figures. Proceedings of SemiMag2000, Matsue, Japan. To be published in Physica B

The ground states of N-electron parabolic quantum dots in the presence of a perpendicular magnetic field are investigated. Rigorous lower bounds to the ground-state energies are obtained. It is shown that our lower bounds agree well with the results of exact diagonalization. Analytic results for the lower bounds to the ground-state energies of the quantum dots in a strong magnetic field (known as electron molecule) agree very well with numerically calculated lower bounds., Comment: 12 pages, 2 tables. Phys. Lett. A (accepted)

Mesoscopic fluctuations of two-port conductance and four-port resistance between Hall plateaus are studied within a realistic model for a two-dimensional electron gas in a perpendicular magnetic field and a smooth disordered potential. The two-port conductance distribution $P(g)$ is concave between $g=0$ and $g=1$ and is nearly flat between $g=0.2$ and $g=0.8$. These characteristics are consistent with recent observations. The distribution is found to be sharply peaked near the end-points $g=0$ and $g=1$. The distribution functions for the three independent resistances in a four-port Hall bar geometry are, on the other hand, characterized by a central peak and a relatively large width., 11 pages, 5 ps figures, submitted to Phys. Rev. B

At temperatures comparable to the Fermi temperature, we have measured a plasmon enhanced Coulomb drag in a GaAs/AlGaAs double quantum well electron system. This measurement provides a probe of the many-body corrections to the coupled plasmon modes, and we present a detailed comparison between experiment and theory testing the validity of local field theories. Using a perpendicular magnetic field to raise the magnetoplasmon energy we can induce a crossover to single-particle Coulomb scattering., Comment: plain tex, 4 pages, 3 figures, to be published in PRL

We study the magnetic susceptibility of an ensemble of non-interacting electrons confined by parabolic potentials and subjected to a perpendicular magnetic field at finite temperatures. We show that the behavior of the average susceptibility is qualitatively different from that of billiards. When averaged over the Fermi energy the susceptibility exhibits a large paramagnetic response only at certain special field values, corresponding to comensurate classical frequencies, being negligible elsewhere. We derive approximate analytical formulae for the susceptibility and compare the results with numerical calculations., 4 pages, 4 figures, REVTEX

We have measured the transport critical current density J c J of Ag-Bi2223 composite tapes at 77 K in the perpendicular magnetic field B ex ≤ 180 Gauss. The hysteresis behavior of J c J between increasing and decreasing field is observed in zero-field-cooled sample. This hysteresis in J c J can be explained by the contribution of magnetic flux trapped in grains to intergranular current transport. From the hysteresis behavior of J c J , it is found that B p for grains is nearly equal to 50 Gauss, where B p is the field at which the magnetic flux fully penetrates the whole part of grain after zero-field cooling. Using a critical state model and the result of B p, the intragranular critical current density J c G is estimated to be ~450,000 A/cm2 and about ten times higher than the value of J c J .

We report phase sensitive measurements of microwave propagation through a high mobility two dimensional electron gas subjected to a perpendicular magnetic field. Two types of configurations were used, one that allows all wave vectors q, and one that selects only specific q values. The spectrum of edge excitations was studied over a broad frequency span, which allowed us to observe the logarithmic dispersion of edge magneto-plasmons., 12 pages, Postscript only, 4 Postscript figures

The energy levels of two and three anyons in a two-dimensional parabolic quantum dot and a perpendicular magnetic field are computed as power series in 1/|J|, where J is the angular momentum. The particles interact repulsively through a coulombic (1/r) potential. In the two-anyon problem, the reached accuracy is better than one part in 10^5. For three anyons, we study the combined effects of anyon statistics and coulomb repulsion in the ``linear'' anyonic states., Comment: LaTeX, 6 pages, 4 postscript figures

Unreacted MgB2 wires fabricated from SiC-doped precursor material by Hyper Tech Research, Inc. have been used to make small-diameter (14 mm) superconducting coils. All coils made of 500 mm length wires were subjected to hot isostatic pressure (HIP) treatment. The critical current density (Jc) parameters of coils were compared to straight samples characteristics. Both types of samples have been measured in perpendicular magnetic field configuration for Jc and pinning force density (Fp) evaluation. No significant Jc difference between the long wires on coils and straight wires was found. These results suggest that the critical current (Ic) for coils can be determined for straight samples (25 mm). SEM analysis indicated that a small diameter of the coil does not influence the structure of in situ MgB2 wire. (Some figures may appear in colour only in the online journal)

We present transport measurements on a system of two lateral quantum dots in a perpendicular magnetic field. Due to edge channel formation in an open conducting region, the quantum dots are chirally coupled. When both quantum dots are tuned into the Kondo regime simultaneously, we observe a change in the temperature dependence of the differential conductance. This is explained by the RKKY exchange interaction between the two dots. As a function of bias the differential conductance shows a splitting of the Kondo resonance which changes in the presence of RKKY interaction.

We derive a three-dimensional Dirac-cone structure composed of tilted anisotropic Dirac cones around spirally located Dirac points. The Dirac points form a nodal spiral in momentum space due to accidental degeneracy, which can be realized in rhombohedral graphite. Under the interlayer electron hoppings, the Dirac cone varies in orientation and shape along this Dirac-point spiral, like a magic gyro precessing and deforming with time. The cone precession is governed by the hopping along the rhombohedral primitive unit vectors. In a perpendicular magnetic field, the electron orbits are related to different Landau level energies under the same quantization condition. The Landau subbands are thus characterized by a dispersion factor in addition to the zero-mode spectrum determined by the Dirac-point spiral.

The nonlinear temperature dependence of nucleation field (Hn) of [Co/Pt]n multilayer based perpendicular magnetic tunnel junction stacks with wedged Co60Fe20B20 insertion layers is reported. When temperature decreases, the tilted spins away from perpendicular direction near Co60Fe20B20/AlOx interface play dominating role to promote the nucleation process and lower Hn value and even change the sign of Hn. By taking advantage of high temperature annealing under high perpendicular magnetic field, this nonlinear behavior and sign of Hn could be manipulated. The understanding of temperature dependent properties in such system is important for spintronics applications, such as in memory and spin oscillators.

The nonlinear and nonlocal diffusion equation for the relaxing current density $J(\mathbf{r},t)$ in long superconductors of arbitrary cross section in a constant perpendicular magnetic field ${B}_{a}$ is solved exactly by separation of variables in the electric field $E(\mathbf{r},t)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}f(\mathbf{r})g(t)$. This solution includes the limiting cases of longitudinal and transverse geometries and applies to the current-voltage laws $E\ensuremath{\propto}{J}^{n}$ ranging from Ohmic ( $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$) to Bean-like ( $n\ensuremath{\rightarrow}\ensuremath{\infty}$) behavior. The electric field profile $f(\mathbf{r})$ weakly depends on $n$ and becomes universal for $n$ exceeding $\ensuremath{\approx}5$. At large times $t$ one finds $E\ensuremath{\propto}1/{t}^{n/(n\ensuremath{-}1)}$ and $J\ensuremath{\propto}1/{t}^{1/(n\ensuremath{-}1)}$ for $ng1$, and $E\ensuremath{\propto}J\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}t/{\ensuremath{\tau}}_{0})$ for $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$. The contour lines of the creeping $E(\mathbf{r},t)$ coincide with the field lines of $\mathbf{B}(\mathbf{r},t)$ in the remanent state ${B}_{a}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$.

Momentum transfer due to electron-electron interaction (Coulomb drag) between two quantum wells, separated by a distance $d$, in the presence of a perpendicular magnetic field, is studied at low temperatures. We find besides the well known Shubnikov-de Haas oscillations, which also appear in the drag effect, the momentum transfer is markedly enhanced by the magnetic field., Comment: 8 pages, Revtex, 4 Postscript figures are available upon request, Accepted by Mod. Phys. Lett. B

The authors have investigated the current-induced magnetic domain wall (DW) motion in perpendicularly magnetized Co/Ni nanowire with structural inversion asymmetry (SIA). In this system, DW motion to the direction of electric current flow, not electron flow, and high DW velocity up to 110 m/s were confirmed, which have never been observed in Co/Ni systems without SIA. In addition, we found that the DW velocity showed a strong dependence on the perpendicular magnetic field in the range of ±100 Oe. These results suggest that DW in the Co/Ni nanowire with SIA moves in the steady mode, not in the precessional mode.

The electronic structure of lateral superlattices in the presence of a perpendicular magnetic field has been a subject of great interest in the past few years. The evolution of these electronic spectra has been mostly analyzed using weak or strong potential modulation limits. In this work we develop a model, within the tight-binding approximation, that handles potential modulations of arbitrary strength. We show the evolution of Hofstadter-like spectra from weak potential modulation up to the strong modulation case, where the lower bands are characteristic of weakly coupled quantum dots. The crossover from weak to strong potential modulation is clarified.

We study the applicability of composite fermion theory to electrons in two-dimensional parabolically-confined quantum dots in a strong perpendicular magnetic field in the limit of low Zeeman energy. The non-interacting composite fermion spectrum correctly specifies the primary features of this system. Additional features are relatively small, indicating that the residual interaction between the composite fermions is weak. \footnote{Published in Phys. Rev. B {\bf 52}, 2798 (1995).}, 15 pages, 7 postscript figures

Summary Sensitivity of the velocity of a single electron, in the relativistic case, to a perpendicular magnetic field is evaluated by defining a parameter which becomes useful in a number of cases related to dynamical systems. In particular, the ultrarelativistic case is examined.

We consider an exactly solvable two-dimensional model of a two-electron parabolic quantum dot (QD) under the perpendicular magnetic field. We perform a detailed study of the degree of the orbital entanglement of the ground and first excited singlet state depending on the shape of QD, the strength of the effective interaction and the magnetic field. It was found that a degree of entanglement increases with the growth of interaction between electrons. The magnetic field destroys the entanglement of electrons. However, the entanglement in deformed QDs is more stable to the effect of the magnetic field.

The influence of external magnetic field to the critical temperature of the superconductor having an array of hole has been calculated using time dependent Ginzburg-Landau equation. The investigation is done after calculating numerically the resistance produced when the superconductor is driven by electric current and exposed under perpendicular magnetic field fie. The result indicates that the addition of lattice holes to the superconductor exposed on perpendicular magnetic field changes the critical temperature. The changes of the critical current due to the different sizes of holes are also discussed.

We consider the combined effects of large spin-orbit couplings and a perpendicular magnetic field in a 2D honeycomb fermionic lattice. This system provides an elegant setup to generate versatile spin textures propagating along the edge of a sample. The spin-orbit coupling is shown to induce topological phase transitions between a helical quantum spin Hall phase and a chiral spin-imbalanced quantum Hall state. Besides, we find that the spin orientation of a single topological edge state can be tuned by a Rashba spin-orbit coupling, opening an interesting route towards quantum spin manipulation. We discuss the possible realization of our results using cold atoms trapped in optical lattices, where large synthetic magnetic fields and spin-orbit couplings can be engineered and finely tuned. In particular, this system would lead to the observation of a time-reversal-symmetry-broken quantum spin Hall phase., Comment: 8 pages, 3 figures, Accepted in Europhys. Lett. (Dec 2011)

We present experimental studies of the current pumped through a dynamic quantum dot over a wide range of magnetic fields. At low fields we observe repeatable structure indicating increased confinement of the electrons in the dynamic dot. At higher fields (B>3T), we observe structure which changes markedly from device to device suggesting that in this regime the transport is sensitive to local disorder. The results are significant for the development of dynamic quantum dot pumps as quantum standards of electrical current., 5 pages, 4 figures, submitted to J. Appl. Phys. as an invited paper for ICPS-30, 25th-30th July, Seoul, SK

A two-step tempering process was performed on L10 FePt films in a magnetic field. FePt (20 nm) films were firstly annealed at 700 oC for 30 minutes and then tempered at lower temperature in a magnetic field of ~ 3500 Oe along the normal direction of films. The influence of magnetic field on (001) texture of FePt films during the two-step tempering process were investigated. It was shown that (001) orientation was improved and, at the same time, distinct perpendicular anisotropy was obtained in FePt films by two-step tempering in a perpendicular magnetic field when the second temperature was around the Curie temperature of the L10 FePt films.

Measurments of the ac penetration depth of a-MoGe films in the presence of a perpendicular magnetic field reveal an anomaly in the ac response of the vortex lattice at a characteristic temperature below the ${\mathit{H}}_{\mathit{c}2}$(T) line. The field and frequency dependence of this anomaly is found to be consistent with a Kosterlitz-Thouless-type melting of the two-dimensional vortex lattice. Moreover, we observe a crossover in the frequency dependence which suggests that the vortex lattice remains disordered on long length scales below the melting temperature.

The leading contributions to the [ital c]-axis conductivity of layered superconductors arising from superconducting fluctuations of the order parameter are discussed for arbitrary intralayer scattering. The contributions from fluctuations of the normal quasiparticle density of states are shown to be opposite in sign to the Aslamazov-Larkin and Maki-Thompson contributions, leading to a peak in the overall [ital c]-axis resistivity [rho][sub [ital c]]([ital T]) above [ital T][sub [ital c]]. This peak is enhanced by a magnetic field [bold H][parallel][bold [cflx c]]. With increasing [ital H], the relative peak maximum in [rho][sub [ital c]]([ital T],[ital H]) increases in magnitude and is shifted to lower temperatures by an amount proportional to [ital H][sup 2] for weak fields and to [ital H] for strong fields. For comparison, the fluctuation conductivity parallel to the layers has been calculated including the fluctuations of the normal density of states. Our results are discussed in regard to recent experiments with YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] and Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+[delta]].

We have grown thin film composites of and YBa2Cu3O7−x and LaAlO3 by co-sputtering. A film with composition of 10% LaAIO3 by volume had a transition temperature of 58K and critical current density of 1.2 × 106 A/cm2 at 4K. We measured the temperature dependence of the critical current and obtained a good fit with Ginzburg-Landau theory for thin films. A perpendicular magnetic field was applied, and the critical current and pinning force measured. At 70 kOe, the critical current was suppressed only a factor of 4 from its zero-field value. The measured pinning force was 2 × 109 dyn/cm3 at 70 kOe and is comparable to that of YBa2Cu3O7−x films.

The ground state energy of a shallow impurity placed in the center of a circular quantum dot is studied. The effects of the strength of the confinement potential and a perpendicular magnetic field are investigated theoretically.

The ac susceptibility, χ = χ′ + iχő, of a superconducting thin disk in a perpendicular magnetic field is calculated in the critical-state model assuming a field-dependent critical current, Jc(B). We find both analytically and numerically that the asymptotic behavior at large ac-field amplitudes Bam changes from χ ′ ∝ B a m − 3 / 2 and χ ″ ∝ B a m − 1 for the Bean model, to χ ′ ∝ B a m − 3 and χ ″ ∝ B a m − 2 for Jc decreasing with |B|as|B|−1 or faster. In the parametric χ″(χ′) plot the peak of χ″ increases in magnitude and shifts toward χ′ = 0. This allows an easy experimental discrimination between a Bean model behavior, one with Jc(B), and one where flux creep is an ingredient. Account of the B-dependence of Jc improves substantially agreement with available experimental χ″(χ′) data.