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We investigate the superfluidity of a two-component Fermi gas with spin-orbital-angular-momentum coupling (SOAMC). Due to the intricate interplay of SOAMC, two-photon detuning and atom-atom interaction, a family of vortex ground states emerge in a broad parameter regime of the phase diagram, in contrast to the usual case where an external rotation or magnetic field is generally required. More strikingly, an unprecedented vortex state, which breaks the continuous rotational symmetry to a discrete one spontaneously, is predicted to occur. The underlying physics are elucidated and verified by numerical simulations. The unique density distributions of the predicted vortex states enable a direct observation in experiment., 5 pages, 4 figures, and 3 pages supplemental material

The energy and spatial distributions of vortex bound state in superconductors carry important information about superconducting pairing and the electronic structure. Although discrete vortex states, and sometimes a zero energy mode, had been observed in several iron-based superconductors, their spatial properties are rarely explored. In this study, we used low-temperature scanning tunneling microscopy to measure the vortex state of (Li,Fe)OHFeSe with high spatial resolution. We found that the nonzero energy states display clear spatial oscillations with a period corresponding to bulk Fermi wavelength; while in contrast, the zero energy mode does not show such oscillation, which suggests its distinct electronic origin. Furthermore, the oscillations of positive and negative energy states near E_{F} are found to be clearly out of phase. Based on a two-band model calculation, we show that our observation is more consistent with an s_{++} wave pairing in the bulk of (Li, Fe)OHFeSe, and superconducting topological states on the surface.

A magnetic order can be completely suppressed at zero temperature (T), by doping carriers or applying pressure, at a quantum critical point, around which physical properties change drastically. However, the situation is unclear for an electronic nematic order that breaks rotation symmetry. Here, we report nuclear magnetic resonance studies on NaFe_{1-x}Co_{x}As where magnetic and nematic transitions are well separated. The nuclear magnetic resonance spectrum is sensitive to inhomogeneous magnetic fields in the vortex state, which is related to London penetration depth λ_{L} that measures the electron mass m^{*}. We discovered two peaks in the doping dependence of λ_{L}^{2}(T∼0), one at x_{M}=0.027 where the spin-lattice relaxation rate shows quantum critical behavior, and another at x_{c}=0.032 around which the nematic transition temperature extrapolates to zero and the electrical resistivity shows a T-linear variation. Our results indicate that a nematic quantum critical point lies beneath the superconducting dome at x_{c} where m^{*} is enhanced. The impact of the nematic fluctuations on superconductivity is discussed.

One of the most fascinating topics in current quantum physics are hybridised systems, in which different quantum resonators are strongly coupled. Prominent examples are circular resonators with high quality factors that allow the coupling of optical whispering gallery modes to microwave cavities or magnon resonances in optomagnonics. Whispering gallery modes play a special role in this endeavour because of their high quality factor and strong localisation, which ultimately increases the overlap of the wavefunctions of quantum particles in hybridised systems. The hybridisation with magnons, the collective quantum excitations of the electron spins in a magnetically ordered material, is of particular interest because magnons can take over two functionalities: due to their collective nature they are robust and can serve as a quantum memory and, moreover, they can act as a wavelength converter between microwave and THz photons. However, the observation of whispering gallery magnons has not yet been achieved due to the lack of efficient excitation schemes for magnons with large wave vectors in a circular geometry. To tackle this problem, we studied nonlinear 3-magnon scattering as a means to generate whispering gallery magnons. This Letter discusses the basics of this nonlinear mechanism in a confined, circular geometry from experimental and theoretical point of view.

We demonstrate that Bragg scattering from a condensate can be sensitive to the spatial phase distribution of the initial state. This allows preferential scattering from a selected spatial region, and provides a robust signature for a vortex state. We develop an analytic model which accurately describes this phenomenon and we give quantitative predictions for current experimental conditions., 5 pages, 3 figures

We measured the heat capacity ${C}_{p}$ and microwave surface impedance ${Z}_{s}$ in the vortex state of ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$. In contrast to conventional $s$-wave superconductors, ${C}_{p}$ shows a $\sqrt{H}$ dependence. This $\sqrt{H}$ dependence persists even after the introduction of the columnar defects which change the electronic structure of the vortex core regime and destroy the regular vortex lattice. On the other hand, flux flow resistivity is nearly proportional to $H$. These results indicate that the vortex state of ${\mathrm{YNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ is fundamentally different from the conventional $s$-wave counterparts, in that the delocalized quasiparticle states around the vortex core are important, similar to $d$-wave superconductors.

We present the results of a study of the magnetic properties of an array of 34-nm thick Co(100) epitaxial ring magnets, with inner and outer diameters of d(in) = 1.3 microm and d(out) = 1.6 microm, respectively. Magnetic measurements and micromagnetic simulations show that a two step switching process occurs at high fields, indicating the existence of two different stable states. In addition to the vortex state, which occurs at intermediate fields, we have identified a new bi-domain state, which we term the onion state, corresponding to opposite circulation of the magnetization in each half of the ring. The onion state is stable at remanence and undergoes a simple and well characterized nucleation free switching.

We studied the conduction noise spectrum in the vortex state of a high-temperature superconductor, ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{y}$, subject to a uniform driving force. Two characteristic features, a broad-band noise (BBN) and a narrow-band noise (NBN), were observed in the vortex-solid phase. The origin of the large BBN was determined to be plastic motion of the vortices, whereas the NBN was found to originate from the washboard modulation of the translational velocity of the driven vortices. We believe this to be the first observation of washboard noise of dc driven vortices in any superconductor.

Using coupled Ginzburg-Landau equations, the dynamics of hexagonal patterns with broken chiral symmetry are investigated, as they appear in rotating non-Boussinesq or surface-tension-driven convection. We find that close to the secondary Hopf bifurcation to oscillating hexagons the dynamics are well described by a single complex Ginzburg-Landau equation (CGLE) coupled to the phases of the hexagonal pattern. At the bandcenter these equations reduce to the usual CGLE and the system exhibits defect chaos. Away from the bandcenter a transition to a frozen vortex state is found., Comment: 4 pages, 6 figures. Fig. 3a with lower resolution now

A generalized methodology, based on anisotropic angular dependent magnetoresistance measurements, is presented to deconvolute the contributions to the vortex activation energy (i.e., plastic and pinning energies) in the vortex liquid state of high temperature superconductors. Experimental evidence is given for the appearance of a partially entangled liquid vortex state in YBa 2Cu 3O (7) when random quenched and correlated disorders compete, as in twinned melt textured YBa 2Cu 3O (7) quasisingle crystals with Y 2BaCuO (5) precipitates. The hallmark of this new phase is a quench of the c-axis vortex correla-tion length.

Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb confined in a magnetic trap and observe the formation of a vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to four vortices are simultaneously present. We have also measured the lifetime of the single vortex state after turning off the stirring laser beam., Comment: 4 pages, 3 figures

We present the results of a microscopic calculation of the longitudinal thermal conductivity, ${\ensuremath{\kappa}}_{\mathrm{xx}}$, of a $d$-wave superconductor in the mixed state. Our results show an increase in the thermal conductivity with the applied field at low temperatures and a decrease followed by a nearly field independent ${\ensuremath{\kappa}}_{\mathrm{xx}}(H)$ at higher temperatures, in qualitative agreement with the experimental results. We discuss the relationship between the slope of the superconducting gap and the plateau in ${\ensuremath{\kappa}}_{\mathrm{xx}}(H)$.

We have created vortices in two-component Bose-Einstein condensates. The vortex state was created through a coherent process involving the spatial and temporal control of interconversion between the two components. Using an interference technique, we map the phase of the vortex state to confirm that it possesses angular momentum. We can create vortices in either of the two components and have observed differences in the dynamics and stability., Comment: 4 pages with 3 figures

The effect of vortices on quasiparticle transport in cuprate superconductors was investigated by measuring the low temperature thermal conductivity of YBa_2Cu_3O_6.9 in magnetic fields up to 8 T. The residual linear term (as T \to 0) is found to increase with field, directly reflecting the occupation of extended quasiparticle states. A study for different Zn impurity concentrations reveals a good agreement with recent calculations for a d-wave superconductor, thereby shedding light on the nature of scattering by both impurities and vortices. It also provides a quantitative measure of the gap near the nodes.

We report transport measurements in the mixed state of YBa{sub 2}Cu {sub 3}O{sub 7{minus}{delta}} single crystals using a contact geometry which enables control of the gradient of the Lorentz force acting on the vortices. The spatial dependence of the vortex velocity profile in the liquid and solid vortex phases is resolved providing information about the transverse dynamic correlation of vortices. While in the liquid phase the vortices respond locally to the driving force, in the solid regime they show long range velocity correlation over macroscopic distances. At high driving force gradients, vortex-vortex shear stresses exceed the elastic limit and the dynamics is characterized by plastic motion. {copyright} {ital 1999} {ital The American Physical Society}

Solving numerically the 3D non linear Ginzburg-Landau (GL) equations, we study equilibrium and nonequilibrium phase transitions between different superconducting states of mesoscopic disks which are thinner than the coherence length and the penetration depth. We have found a smooth transition from a multi-vortex superconducting state to a giant vortex state with increasing both the disk thickness and the magnetic field. A vortex phase diagram is obtained which shows, as function of the magnetic field, a re-entrant behavior between the multi-vortex and the giant vortex state., Comment: 5 figures (post script files) included

Coherent terahertz spectroscopy is used to measure the complex conductivity of thin films of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ in the vortex state as a function of frequency, temperature, and applied magnetic field. We report an unusual sublinear power law dependence of the high-frequency magnetoconductivity $\ensuremath{\Delta}\ensuremath{\sigma}(H)\ensuremath{\equiv}\ensuremath{\sigma}(H)\ensuremath{-}\ensuremath{\sigma}(0)$ on magnetic field. Over a broad range of field and temperature, $\ensuremath{\Delta}{\ensuremath{\sigma}}_{2}$ varies as ${H}^{\ensuremath{\alpha}}$, with $\ensuremath{\alpha}\ensuremath{\approx}\frac{1}{2}$. We present a model based on the nonlinear London electrodynamics predicted for a $d$-wave superconductor which quantitatively explains these results using only parameters obtained from zero-field measurements.

We calculate the magnetic field dependence of quasiparticle transport properties in the vortex state of a $d$-wave superconductor arising solely from the quasiparticle's Doppler shift in the superflow field surrounding the vortex. Qualitative features agree well with experiments on cuprate and heavy fermion superconductors at low fields and temperatures. We derive scaling relations in the variable $T/{H}^{1/2}$ valid at sufficiently low temperatures $T$ and fields $H$, but show that these relations depend on the scattering phase shift, and are fulfilled only approximately even in the clean limit.

We examine a vortex phase diagram for high- ${T}_{c}$ superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ when columnar defects are introduced by heavy-ion irradiation, by using Monte Carlo simulation based on the Lawrence-Doniach model. At finite temperatures, we numerically find a magnetic-field-driven discontinuous transition in the trapping rate of ``pancake'' vortices to the defects, at a critical field of $B/{B}_{\ensuremath{\Phi}}\ensuremath{\simeq}1/3$ below the matching field ${B}_{\ensuremath{\Phi}}$. The transition in the vortex liquid phase is accompanied by a discontinuous jump of the interlayer coherence, where the decoupled vortex liquid appears to partially couple along the defects.

Magnetic penetration depths in the mixed state of a heavy-fermion superconductor CeRu{sub 2} have been measured by muon spin rotation. An anomalous increase of the observed penetration depth associated with the hysteresis peak of magnetization strongly suggests a new vortex phase, possibly a generalized Fulde-Ferrel-Larkin-Ovchinnikov state, near the upper critical field. {copyright} {ital 1997} {ital The American Physical Society}

The internal field distribution in the vortex state of YBa{sub 2}Cu {sub 3}O{sub 6.60} is shown to be a sensitive measure of both the magnetic penetration depth {lambda}{sub ab} and the vortex-core radius {rho}{sub 0} . The temperature dependence of {rho}{sub 0} is found to be weaker than in the conventional superconductor NbSe{sub 2} and much weaker than theoretical predictions for an isolated vortex. The effective vortex-core radius decreases sharply with increasing H , whereas {lambda}{sub ab}(H) is found to be much stronger than in NbSe{sub 2} . {copyright} {ital 1997} {ital The American Physical Society}

We have measured the critical current density j{sub c} as a function of the orientation of a magnetic field in vicinal YBa{sub 2}Cu {sub 3}O{sub 7{minus}{delta}} films. When both field and Lorentz force lie within the ab plane, we observe a minimum in j{sub c} . At high temperatures, as the c -axis coherence length approaches the ab -plane distance, the minimum in j{sub c} could not be observed, indicating that this effect is related to the breakdown of the rectilinear vortex state for fields at a small angle to the ab planes. Our results are the first demonstration of intrinsic channeling of vortex strings along the ab planes. {copyright} {ital 1997} {ital The American Physical Society}

Muon-spin rotation spectroscopy $(\ensuremath{\mu}\mathrm{SR})$ has been used to measure the internal magnetic field distribution in ${\mathrm{NbSe}}_{2}$ for ${H}_{c1}\ensuremath{\ll}Hl{0.25H}_{c2}$. The deduced profiles of the supercurrent density ${J}_{s}$ indicate that the vortex-core radius ${\ensuremath{\rho}}_{0}$ in the bulk decreases sharply with increasing magnetic field. This effect, which is attributed to increased vortex-vortex interactions, does not agree with the dirty-limit microscopic theory. A simple phenomenological equation in which ${\ensuremath{\rho}}_{0}$ depends on the intervortex spacing is used to model this behavior. In addition, we find for the first time that the in-plane magnetic penetration depth ${\ensuremath{\lambda}}_{\mathrm{ab}}$ increases linearly with $H$ in the vortex state of a conventional superconductor.

We present measurements of a dynamically induced instability in the vortex state of an amorphous multilayer and a single alloy layer of Ta/Ge. The critical vortex velocity shows quantitative agreement with the predictions of Larkin and Ovchinnikov calculated using parameters determined independently from the normal state resistivity data. Both samples show a weak field dependence in the critical velocity implying a velocity dependent pinning force in the vortex solid state and a broadening of the transition resulting from the velocity distribution in the liquid state. {copyright} {ital 1997} {ital The American Physical Society}

Phase transitions in spherical particles of a cubic ferroelectric are considered within Landau-Ginzburg-Devonshire theory. Concentrating on effects of the depolarizing field, we study competition between states with homogeneous polarization and vortex structures. For large radii of the sphere (R>Rc), the phase transition is into a vortex state while for R

An outline of the state space of planar Couette flow at high Reynolds numbers ($Re < 10^5$) is investigated via a variety of efficient numerical techniques. It is verified from nonlinear analysis that the lower branch of {\it Hairpin Vortex State} (HVS) asymptotically approaches the primary (laminar) state with increasing $Re$. It is also predicted that the lower branch of HVS at high $Re$ belongs to the stability boundary that initiates transition to turbulence, and that one of the unstable manifolds of the lower branch of HVS lies on the boundary. These facts suggest HVS may provide a criterion to estimate a minimum perturbation arising transition to turbulent states at the infinite $Re$ limit., 4 pages, 3 figures

We have used torsional oscillators, containing disk-shaped slabs of superfluid $^{3}\mathrm{He}$-$A$, to probe the chiral orbital textures created by cooling into the superfluid state while continuously rotating. Comparing the observed flow-driven textural transitions with numerical simulations of possible textures shows that an oriented monodomain texture with $\stackrel{^}{\mathbit{l}}$ antiparallel to the angular velocity ${\mathbf{\ensuremath{\Omega}}}_{0}$ is left behind after stopping rotation. The bias toward a particular chirality, while in the vortex state, is due to the inequivalence of energies of vortices of opposite circulation. When spun-up from rest, the critical velocity for vortex nucleation depends on the sense of rotation relative to that of $\stackrel{^}{\mathbit{l}}$. A different type of vorticity, apparently linked to the slab's rim by a domain wall, appears when the angular velocity, $\mathbf{\ensuremath{\Omega}}$, is parallel to $\stackrel{^}{\mathbit{l}}$.

We have measured the microwave surface resistance (30-60 GHz) for different crystallographic orientations in the vortex state of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. A sharp magnetoabsorption resonance is observed below ${T}_{c}$ when ac electric fields and magnetic fields are applied parallel to the $c$ axis (${E}_{\mathrm{ac}}\ensuremath{\parallel}B\ensuremath{\parallel}c$). We argue that the observed resonance arises from collective Josephson plasma oscillations generated by interlayer Josephson currents. From the frequency and temperature dependence of the resonance, we discuss the interlayer phase coherence in the vortex liquid and solid states quantitatively.

The depinned vortex lattice in a type II superconductor represents a periodic structure moving in a random distribution of pinning centers. Such a system displays a ``washboard'' frequency given by $\ensuremath{\omega}/2\ensuremath{\pi}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}v/a$ where $v$ is the velocity and $a$ the lattice period. By mixing a dc and an ac current (of frequency ${\ensuremath{\omega}}_{\mathrm{ext}}$), we demonstrate the existence of the washboard effect in the vortex state in an untwinned crystal of YB${\mathrm{a}}_{2}$C${\mathrm{u}}_{3}$${\mathrm{O}}_{6.93}$. Jumps in the dc current-voltage characteristics are observed when $\ensuremath{\omega}$ and ${\ensuremath{\omega}}_{\mathrm{ext}}$ are harmonically related. We show that these jumps vanish when the line at the solid-to-liquid transition is crossed.

We report on transport measurements in the mixed state of YBa[sub 2]Cu[sub 3]O[sub 7] single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on Bi[sub 2]Sr[sub 2]CaCu[sub 2]O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in YBa[sub 2]Cu[sub 3]O[sub 7] is a line liquid.

We report muon-spin-rotation (\ensuremath{\mu}SR) measurements of the a-b magnetic penetration depth (${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$) in the vortex state of high quality single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.95}$. Contrary to earlier \ensuremath{\mu}SR studies on powders and crystal mosaics, 1/${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}^{2}$ shows a strong linear temperature dependence below 50 K which weakens with increasing magnetic field. These results support recent microwave cavity measurements in zero field and provide further evidence for unconventional pairing of carriers.

Experimental evidence of a Bose-glass transition in the vortex state of YBa2Cu3O7 single crystals with columnar defects along the c axis is manifested by the universal critical exponents ν⊥, ν∥ (≡ζν⊥), and z’ derived from the (d’+1)-dimension critical scaling of the frequency-dependent ac resistivity from 102 to 2.5×106 Hz. The Bose-glass transition temperature (TBG) is found to decrease with the increasing angle (θ) between the applied magnetic field and the c axis. The finding that ζ=ν∥/ν⊥=1.1±0.1

Swept-frequency measurements (1-600 MHz) of the vortex resistivity in YBa 2 Cu 3 O 7 were performed in fields from 0.5 to 8 T. At all fields studied, both the real and imaginary parts of the resistivity display a power-law frequency dependence with exponents α 1 and α 2 that depend only on the reduced field h=H/H * (T). The scaling field H * (T) is identified with the critical field for the solid-to-liquid transition

A scaling behavior of the Hall resistivity in a mixed state of high-${\mathit{T}}_{\mathit{c}}$ superconductors is shown to be a general feature of any vortex state with disorder-dominated dynamics (thermally assisted flux flow, vortex glass, etc.). The universal scaling law ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$\ensuremath{\propto}${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}^{2}$ is found. The presented theory agrees with recent experimental data.

Cichorek et al. [Phys. Rev. Lett. 94, 107002 (2005)] reported enhancements of the lower critical field Hc1(T) and critical current in superconducting PrOs4Sb12 below a transition temperature Tc3 ~ 0.6 K, and speculated that this reflects a transition between superconducting phases. Features have been observed near Tc3 in other properties, but not in the specific heat. We report muon spin rotation measurements of the penetration depth in the vortex state of PrOs4Sb12 near Hc1(T), that to high accuracy exhibit no anomaly Tc3 and therefore cast doubt on the putative phase transition.

We use Raman-detuned laser pulses to achieve spatially-varying control of the amplitude and phase of the spinor order parameter of a Bose-Einstein condensate. We present experimental results confirming precise radial and azimuthal control of amplitude and phase during the creation of vortex-antivortex superposition states., Comment: 4 pages, 6 figures, accepted to PRL

We investigate the behavior of the thermal conductivity \ensuremath{\kappa}(H) of both twinned and untwinned single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ in a magnetic field. Remanant field data are examined in the framework of the Bean critical state model and thermally activated flux creep. In-field data are shown to depart from conventional superconductor models. The \ensuremath{\kappa}(H) profie is fitted by a phenomenological form and is suggested to originate from Bloch wave travel of phonons through a vortex array which becomes more regular as the field increases.

Local-magnetic-field distributions in the superconducting mixed state of high-${\mathit{T}}_{\mathit{c}}$ cuprates were measured by muon-spin rotation (\ensuremath{\mu}SR) in the absence of applied driving forces. In this first analytical treatment, a critical-state model, incorporating an anisotropic penetration depth [${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$(0)=1300\ifmmode\pm\else\textpm\fi{}100 \AA{} in the basal plane], reveals the strong influence of local pinning on the characteristic shape of low-temperature \ensuremath{\mu}SR Fourier spectra for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The linewidths are found to be nearly independent of flux density, indicative of noncollective or local pinning.

Using a SQUID picovoltmeter. we have measured current-voltage curves of YBa2Cu3O7 microtwinned crystals as a function of temperature in fields from I to 6 T. The data constitute evidence for a finite-temperature phase transition in the vortex state. Exponents derived within the framework of the vortex-glass model are found to be similar to thin-film values. Strongly temperature-dependent correlations in-volving up to 105 vortices near the transition. combined with the qualitative failure of thermal-activation models to fit our data. support the existence of a phase transition.

We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor ${\mathrm{KOs}}_{2}{\mathrm{O}}_{6}$ (${T}_{c}=9.6\text{ }\text{ }\mathrm{K}$) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31--40 \AA{}, in agreement with the value derived from the upper critical field ${H}_{\mathrm{c}2}$. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.

We discuss thermally activated resistivity of strongly layered high-temperature superconductors such as Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} in the limit in which the dominant pinning mechanism is the intrinsic pinning due to the layered structure. From a comparison of our theory with the experimental data we conclude that the vortex state of such superconductors must be disordered over a substantial range of parameters---a melted liquid. The magnetic field, the temperature, and the current dependence of the calculated activation energy are consistent with experiments.

A Zeeman magnetic field can induce a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase in spin-singlet superconductors. Here we argue that there is a nontrivial solution for the FFLO vortex phase that exists near the upper critical field in which the wave function has only spatial line nodes that form intricate and unusual three-dimensional structures. These structures include a crisscrossing lattice of two sets of nonparallel line nodes. We show that these solutions arise from the decay of conventional Abrikosov vortices into pairs of fractional vortices. We propose that neutron scattering studies can observe these fractional vortex pairs through the observation of a lattice of 1/2 flux quanta vortices. We also consider related phases in noncentrosymmetric superconductors.

The spin-transfer effect is investigated for the vortex state of a magnetic nanodot. A spin current is shown to act similarly to an effective magnetic field perpendicular to the nanodot. Then a vortex with magnetization (polarity) parallel to the current polarization is energetically favorable. Following a simple energy analysis and using direct spin--lattice simulations, we predict the polarity switching of a vortex. For magnetic storage devices, an electric current is more effective to switch the polarity of a vortex in a nanodot than the magnetic field.

We have used terahertz spectroscopy to measure the Josephson plasma resonance in the superconductor Tl2Ba2CaCu2O8+delta. This allows us to probe the longitudinal ordering of pancake vortices as a function of applied ab-plane current in a 2.5 kG c-axis magnetic field. With increasing current in the low temperature vortex solid phase, we observe a decrease in the interlayer phase coherence consistent with a progressive misalignment of the pancake vortices in neighboring layers. In the high temperature vortex liquid phase, an increase in the longitudinal ordering occurs above a certain threshold current. Our results show evidence of a current-driven coupling-decoupling crossover in the pinned liquid phase.

We consider a quasi-two-dimensional superconductor with line nodes in the presence of an in-plane magnetic field, and compute the dependence of the specific heat C and the in-plane heat conductivity kappa on the angle between the field and the nodal direction in the vortex state. We use a variation of the microscopic Brandt-Pesch-Tewordt method that accounts for the scattering of quasiparticles off vortices, and analyze the signature of the nodes in C and kappa. At low to moderate fields the specific heat anisotropy changes sign with increasing temperature. Comparison with measurements of C and kappa in CeCoIn(5) resolves the contradiction between the two in favor of the d((x(2)-y(2)) gap.

We investigate the effects of an external magnetic field in the gluon dynamics of a color superconductor with three massless quark flavors. In the framework of gluon mean-field theory at asymptotic densities, we show that the long-range component $\widetilde{H}$ of the external magnetic field that penetrates the CFL phase produces an instability when its strength becomes larger than the Meissner mass of the charged gluons. As a consequence, the magnetic field causes the formation of a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. Inside the flux tubes the magnetic field is stronger than the applied one. This antiscreening effect is connected to the anomalous magnetic moment of the gluon field. We suggest how this same mechanism could serve to remove the chromomagnetic instabilities existing in gapless color superconductivity., Version to appear in PRL. Typos corrected and several references added

We study a twisted vortex bundle where quantized vortices form helices circling around the axis of the bundle in a "force-free" configuration. Such a state is created by injecting vortices into rotating vortex-free superfluid. Using continuum theory we determine the structure and the relaxation of the twisted state. This is confirmed by numerical calculations. We also present experimental evidence of the twisted vortex state in superfluid 3He-B., Comment: 5 pages, 4 figures, RevTeX file, corrected after the referee comments