Publications (972)2400.8 Total impact
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ABSTRACT: BoseEinstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photoand chemically doped UO 2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atombased system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultralow temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.  [Show description] [Hide description]
DESCRIPTION: The dynamical behavior of a higherorder nonlinear Schr\"{o}dinger equation is found to include a very wide range of scenarios due to the interplay of higherorder physically relevant terms. The dynamics extends from Poincar\'{e}Bendixsontype scenarios, in the sense that bounded solutions may converge either to distinct equilibria via orbital connections, or spacetime periodic solutions, to the emergence of almost periodic and chaotic behavior. Suitable lowdimensional phase space diagnostics are developed and are used to illustrate the different possibilities and to identify their respective parametric intervals.  [Show abstract] [Hide abstract]
ABSTRACT: The dynamical behavior of a higherorder cubic GinzburgLandau equation is found to include a very wide range of scenarios due to the interplay of higherorder physically relevant terms. The dynamics extend from Poincar\'eBendixsontype scenarios, in the sense that bounded solutions may converge either to distinct equilibria via orbital connections, or spacetime periodic solutions, to the emergence of almost periodic and chaotic behavior. Suitable lowdimensional phase space diagnostics are developed and used to illustrate the different possibilities and identify their respective parametric intervals over multiple parameters of the model.  [Show abstract] [Hide abstract]
ABSTRACT: Our current understanding of strongly correlated electron systems is based on a homogeneous framework. Here we take a step going beyond this paradigm by incorporating inhomogeneity from the beginning. Specifying to systems near the Mott metalinsulator transition, we propose a real space picture of itinerant electrons functioning in the fluctuating geometries bounded by interfaces between metallic and insulating regions. In 2+1dimensions, the interfaces are closed bosonic strings, and we have a system of strings coupled to itinerant electrons. When the interface tension vanishes, the geometric fluctuations become critical, which gives rise to nonFermi liquid behavior for the itinerant electrons. The fermion selfenergy scales as the square root of frequency, and the dc resistivity is linear in temperature. Furthermore, the quantum geometric fluctuations mediate Cooper pairing among the itinerant electrons, indicating the instrinsic instability of electronic systems near the Mott transition, in contrast to predictions based on a homogeneous framework.  [Show abstract] [Hide abstract]
ABSTRACT: In the present work, we consider the selffocusing discrete nonlinear Schrodinger equation on hexagonal and honeycomb lattice geometries. Our emphasis is on the study of the effects of anisotropy, motivated by the tunability afforded in recent optical and atomic physics experiments. We find that important classes of solutions, such as the socalled discrete vortices, undergo destabilizing bifurcations as the relevant anisotropy control parameter is varied. We quantify these bifurcations by means of explicit analytical calculations of the solutions, as well as of their spectral linearization eigenvalues. Finally, we corroborate the relevant stability picture through direct numerical computations. In the latter, we observe the prototypical manifestation of these instabilities to be the spontaneous rearrangement of the solution, for larger values of the coupling, into localized waveforms typically centered over fewer sites than the original unstable structure. For weak coupling, the instability appears to result in a robust breathing of the relevant waveforms.  [Show abstract] [Hide abstract]
ABSTRACT: Allostery through DNA is increasingly recognized as an important modulator of DNA functions. Here, we show that the coalescence of proteininduced DNA bubbles can mediate allosteric interactions that drive protein aggregation. We propose that such allostery may regulate DNA's flexibility and the assembly of the transcription machinery. Mitochondrial transcription factor A (TFAM), a dualfunction protein involved in mitochondrial DNA (mtDNA) packaging and transcription initiation, is an ideal candidate to test such a hypothesis owing to its ability to locally unwind the double helix. Numerical simulations demonstrate that the coalescence of TFAMinduced bubbles can explain experimentally observed TFAM oligomerization. The resulting melted DNA segment, approximately 10 base pairs long, around the joints of the oligomers act as flexible hinges, which explains the efficiency of TFAM in compacting DNA. Since mitochondrial polymerase (mitoRNAP) is involved in melting the transcription bubble, TFAM may use the same allosteric interaction to both recruit mitoRNAP and initiate transcription.  [Show abstract] [Hide abstract]
ABSTRACT: A stability criterion for solitons of the driven nonlinear Schrödinger equation (NLSE) has been conjectured. The criterion states that p^{'}(v)<0 is a sufficient condition for instability, while p^{'}(v)>0 is a necessary condition for stability; here, v is the soliton velocity and p=P/N, where P and N are the soliton momentum and norm, respectively. To date, the curve p(v) was calculated approximately by a collective coordinate theory, and the criterion was confirmed by simulations. The goal of this paper is to calculate p(v) exactly for several classes and cases of the generalized NLSE: a soliton moving in a real potential, in particular a timedependent ramp potential, and a timedependent confining quadratic potential, where the nonlinearity in the NLSE also has a timedependent coefficient. Moreover, we investigate a logarithmic and a cubic NLSE with a timeindependent quadratic potential well. In the latter case, there is a bisoliton solution that consists of two solitons with asymmetric shapes, forming a bound state in which the shapes and the separation distance oscillate. Finally, we consider a cubic NLSE with parametric driving. In all cases, the p(v) curve is calculated either analytically or numerically, and the stability criterion is confirmed.  [Show abstract] [Hide abstract]
ABSTRACT: A stability criterion for solitons of the driven nonlinear Schr\"odinger equation (NLSE) has been conjectured. The criterion states that ${p}^{$'${}}(v)<0$ is a sufficient condition for instability, while ${p}^{$'${}}(v)>0$ is a necessary condition for stability; here, $v$ is the soliton velocity and $p=P/N$, where $P$ and $N$ are the soliton momentum and norm, respectively. To date, the curve $p(v)$ was calculated approximately by a collective coordinate theory, and the criterion was confirmed by simulations. The goal of this paper is to calculate $p(v)$ exactly for several classes and cases of the generalized NLSE: a soliton moving in a real potential, in particular a timedependent ramp potential, and a timedependent confining quadratic potential, where the nonlinearity in the NLSE also has a timedependent coefficient. Moreover, we investigate a logarithmic and a cubic NLSE with a timeindependent quadratic potential well. In the latter case, there is a bisoliton solution that consists of two solitons with asymmetric shapes, forming a bound state in which the shapes and the separation distance oscillate. Finally, we consider a cubic NLSE with parametric driving. In all cases, the $p(v)$ curve is calculated either analytically or numerically, and the stability criterion is confirmed.  [Show abstract] [Hide abstract]
ABSTRACT: We consider a twodimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anticontinuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only singlesite excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual "extended" unstaggered bright solitons, in which all sites are excited in the AC limit, with the same sign across the lattice (they represent the most robust states supported by the lattice, their 1D counterparts being what was considered as 1D bright solitons in the abovementioned work), and the vortex cross, which is specific to the 2D setting. For all the existing states, we explore their stability (analytically, whenever possible). Typical scenarios of instability development are exhibited through direct simulations.  [Show abstract] [Hide abstract]
ABSTRACT: Schizophrenia (SZ) genomewide association studies (GWASs) have identified common risk variants in >100 susceptibility loci; however, the contribution of rare variants at these loci remains largely unexplored. One of the strongly associated loci spans MIR137 (miR137) and MIR2682 (miR2682), two microRNA genes important for neuronal function. We sequenced ∼6.9 kb MIR137/MIR2682 and upstream regulatory sequences in 2,610 SZ cases and 2,611 controls of European ancestry. We identified 133 rare variants with minor allele frequency (MAF) <0.5%. The rare variant burden in promoters and enhancers, but not insulators, was associated with SZ (p = 0.021 for MAF < 0.5%, p = 0.003 for MAF < 0.1%). A rare enhancer SNP, 1:g.98515539A>T, presented exclusively in 11 SZ cases (nominal p = 4.8 × 10(4)). We further identified its risk allele T in 2 of 2,434 additional SZ cases, 11 of 4,339 bipolar (BP) cases, and 3 of 3,572 SZ/BP study controls and 1,688 population controls; yielding combined p values of 0.0007, 0.0013, and 0.0001 for SZ, BP, and SZ/BP, respectively. The risk allele T of 1:g.98515539A>T reduced enhancer activity of its flanking sequence by >50% in human neuroblastoma cells, predicting lower expression of MIR137/MIR2682. Both empirical and computational analyses showed weaker transcription factor (YY1) binding by the risk allele. Chromatin conformation capture (3C) assay further indicated that 1:g.98515539A>T influenced MIR137/MIR2682, but not the nearby DPYD or LOC729987. Our results suggest that rare noncoding risk variants are associated with SZ and BP at MIR137/MIR2682 locus, with risk alleles decreasing MIR137/MIR2682 expression. Copyright © 2014 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.  [Show abstract] [Hide abstract]
ABSTRACT: We show that a mesoscale model, with a minimal number of parameters, can describe well the thermomechanical and mechanochemical behavior of homogeneous DNA at thermal equilibrium under tension and torque. We predict critical temperatures for denaturation under torque and stretch, phase diagrams for stable DNA, probe/response profiles under mechanical loads, and the density of dsDNA as a function of stretch and twist. We find strong agreement with available single molecule manipulation experiments.  [Show abstract] [Hide abstract]
ABSTRACT: The inverse square potential arises in a variety of different quantum phenomena, yet notoriously it must be handled with care: it suffers from pathologies rooted in the mathematical foundations of quantum mechanics. We show that its recently studied conformality breaking corresponds to an infinitely smooth windingunwinding topological transition for the classical statistical mechanics of a onedimensional system: this describes the tangling or untangling of floppy polymers under a biasing torque. When the ratio between torque and temperature exceeds a critical value the polymer undergoes tangled oscillations, with an extensive winding number. At lower torque or higher temperature the winding number per unit length is zero. Approaching criticality, the correlation length of the order parameterthe extensive winding numberfollows a KosterlitzThoulesstype law. The model is described by the Wilson line of a (0+1) U(1) gauge theory, and applies to the tangling or untangling of floppy polymers and to the winding or diffusing kinetics in diffusionconvection reactions.  [Show abstract] [Hide abstract]
ABSTRACT: A nonHermitian quantum optimization algorithm is created and used to find the ground state of an antiferromagnetic Ising chain. We demonstrate analytically and numerically (for up to N=1024 spins) that our approach leads to a significant reduction of the annealing time that is proportional to $\ln N$, which is much less than the time (proportional to $N^2$) required for the quantum annealing based on the corresponding Hermitian algorithm. We propose to use this approach to achieve similar speedup for NPcomplete problems by using classical computers in combination with quantum algorithms. 
Article: Role of complex energy landscapes and strains in multiscale inhomogeneities in perovskite manganites
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ABSTRACT: We analyze the essential role played by complex energy landscapes in the nanometer to micronscale inhomogeneities observed in perovskite manganites using a model expressed in terms of symmetrized atomicscale lattice distortion modes. We also examine the stability of large metal and insulator domains in the absence of defects. Our results demonstrate that an intrinsic mechanism, which involves longrange interactions between strain fields, the PeierlsNabarro energy barrier, and complex energy landscapes with multiple metastable states, rather than an extrinsic mechanism such as chemical randomness, is responsible for the inhomogeneity in perovskite manganites.  [Show abstract] [Hide abstract]
ABSTRACT: We study the stable states of the wave equation with dspatial and 1time dimensions and with spacetime periodic potential. The dispersed stable states spectrum of such periodic wave equation is due to the incommensurability of the speed of light and the ratio of space and time periods. A BlochFloquet analysis leads to a cube as a reduced Brillouin zone, but because of the speed incommensurability the stable states in this cube may form a spectrum of sets with a reduced dimensionality. For electromagnetic waves in photonic crystals the medium may amplify some waves with lengths fitting the crystal lattice. The energy from the external field can be pumped to the waves via the dipole moment oscillations.  [Show abstract] [Hide abstract]
ABSTRACT: Xray pair distribution function (pdf) and U L 3 extended xray absorption fine structure (EXAFS) and neutron pdf measurements that give identical results for UO 2 show U(VI)oxo moieties with x rays for mixed valence U 4 O 9 and U 3 O 7 , in contrast to the neutron data that indicate only U(V) sites with no short UO bonds as well as other differences. In addition, although the EXAFS spectra of UO 2 are essentially identical at 30, 100, and 200 K, those of the UO 2+x compounds exhibit different nearestneighbor UO distributions at each temperature. Further tunneling polarontype behavior is found in the broadening of the features of the O Kedge xray absorption spectra (XAS) of the UO 2+x compounds. Raman spectra of powders also show a large increase in scattering cross section with increasing O content that would originate in a change in the electronic structure that increases the overall polarizability. The XAS and Raman also show that U 4 O 9 does not behave as a linear combination of the UO 2 and U 3 O 7 fluorite endpoints. The properties induced by mobile rather than static charged quasiparticles were explored by optical pumping of the metaltometal chargetransfer transition. The temperature dependence of 4.71 eV pump–1.57 eV probe reflectivity on UO 2 that initially populates the U 6ddominated portion of the upper Hubbard band (UHB) shows a sharp 28μsec lifetime peak at 25 K that may be associated with the fluctuations of its antiferromagnetic transition. Pumping at 3.14 eV into the 5f dominated portion of the UHB shows an analogous 2.8μsec peak but also a plateau bracketing this peak that ends in a cusp at 50–60 K and an abrupt change in the hardening rate of a novel 12–15 GHz phonon that is the signature for the quasiparticle quantum phase. The different results for the different excitation channels indicate a highly specific nonthermal relaxation mechanism. These results constitute the first observation of a distinct phase of photoinduced quasiparticles that is sufficiently coupled to the lattice to undergo a gapopening transition. When the intragap state is probed with a terahertz time domain spectroscopy (TTDS) measurement 33 psec after a 3.14 excitation pulse, it shows increased absorption in the 0.5–1.1 THz range with a decrease in temperature from ∼30 to 10 K instead of the expected decrease, a result consistent with the presence of a condensate. These results are too extreme to originate in the dynamical, nonadiabatic, coupled chargetransfer–phonon/tunneling polaron scenario previously used for doped MottHubbard insulators with intermediate electronphonon coupling and therefore indicate novel physics. One possibility that could cause all of these behaviors is that a collective, dynamical, charge transfercoupled Peierls distortion involving the 2 U(V) ↔ U(IV) + U(VI)oxo excitation occurs coherently over an entire domain to cause the atoms in this domain to condense into a system with BoseEinstein or BoseEinsteinHubbard properties. 
Article: Static and dynamic phases for magnetic vortex matter with attractive and repulsive interactions
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ABSTRACT: Exotic vortex states with long range attraction and short range repulsion have recently been proposed to arise in certain superconducting hybrid structures such as typeI/typeII layered systems as well as multiband superconductors. In previous work it has been shown that such systems can form clump or phase separated states, but little is known about how they behave in the presence of pinning and under an applied drive. Using large scale simulations we examine the static and dynamic properties of such vortex states interacting with random and periodic pinning. In the absence of pinning this system does not form patterns but instead undergoes complete phase separation. When pinning is present there is a transition from inhomogeneous to homogeneous vortex configurations similar to a wetting phenomenon. Under an applied drive, a dynamical dewetting process can occur from a strongly pinned homogeneous state into pattern forming states, such as moving stripes that are aligned with the direction of drive or moving labyrinth or clump phases. We show that a signature of the exotic vortex interactions observable with transport measurements is a robust double peak feature in the differential resistance curves. Our results should be valuable for determining whether such vortex interactions are occurring in these systems and also for addressing the general problem of systems with competing interactions in the presence of random and periodic pinning.  [Show abstract] [Hide abstract]
ABSTRACT: Sparse matrixvector multiplication (spMVM) is the most timeconsuming kernel in many numerical algorithms and has been studied extensively on all modern processor and accelerator architectures. However, the optimal sparse matrix data storage format is highly hardwarespecific, which could become an obstacle when using heterogeneous systems. Also, it is as yet unclear how the wide single instruction multiple data (SIMD) units in current multi and manycore processors should be used most efficiently if there is no structure in the sparsity pattern of the matrix. We suggest SELLCsigma, a variant of Sliced ELLPACK, as a SIMDfriendly data format which combines longstanding ideas from General Purpose Graphics Processing Units (GPGPUs) and vector computer programming. We discuss the advantages of SELLCsigma compared to established formats like Compressed Row Storage (CRS) and ELLPACK, and show its suitability on a variety of hardware platforms (Intel Sandy Bridge, Intel Xeon Phi and Nvidia Tesla K20) for a wide range of test matrices from different application areas. Using appropriate performance models we develop deep insight into the data transfer properties of the SELLCsigma spMVM kernel. SELLCsigma comes with two tuning parameters whose performance impact across the range of test matrices is studied and for which reasonable choices are proposed. This leads to a hardwareindependent ("catchall") sparse matrix format, which achieves very high efficiency for all test matrices across all hardware platforms.  [Show abstract] [Hide abstract]
ABSTRACT: We study the RKKY interaction in nonFermiliquid metals. We find that the RKKY interaction mediated by some nonFermiliquid metals can be of much longer range than for a Fermi liquid. The oscillatory nature of the RKKY interaction thus becomes more important in such nonFermi liquids, and gives rise to enhanced frustration when the spins form a lattice. Frustration suppresses the magnetic ordering temperature of the lattice spin system. Furthermore, we find that the spin system with a longer range RKKY interaction can be described by the Brazovskii model, where the ordering wave vector lies on a higher dimensional manifold. Strong fluctuations in such a model lead to a firstorder phase transition and/or glassy phase. This may explain some recent experiments where glassy behavior was observed in stoichiometric heavy fermion material close to a ferromagnetic quantum critical point.  [Show abstract] [Hide abstract]
ABSTRACT: We numerically examine vortex matter with repulsive interactions at short range and attractive interactions at long range in the presence of periodic pinning arrays. Such competing vortex interactions are predicted to occur in multiband superconductors or typeI and typeII hybrid materials. For weak pinning, the vortices form cluster states, while for strong pinning, the vortices form uniform states in which flux is evenly distributed among the pinning sites. As a function of external drive, the weak pinning system exhibits clump depinning with no structure changes, while the strong pinning system depins into a disordered fluctuating state followed by a transition to a partially aligned stripe state. For weak pinning, there is a single peak in the differential conductivity, while for strong pinning there are two peaks, indicating that transport curves could be used to distinguish between vortex systems with purely repulsive interactions and those with additional long range attractive interactions.
Publication Stats
20k  Citations  
2,400.80  Total Impact Points  
Top Journals
 Physical review. B, Condensed matter (135)
 Physical Review B (59)
 Synthetic Metals (50)
 Physical Review E (46)
 Physical Review Letters (39)
Institutions

19702015

Los Alamos National Laboratory
 • Center for Nonlinear Studies
 • Theoretical Division
 • Superconductivity Technology Center
ЛосАламос, California, United States


20092012

Beth Israel Deaconess Medical Center
 Department of Medicine
Boston, Massachusetts, United States


2007

McGill University
 Department of Physics
Montréal, Quebec, Canada


2006

Université ParisSud 11
Orsay, ÎledeFrance, France 
Occidental College
 Department of Physics
Los Ángeles, California, United States 
Università degli Studi di Trento
Trient, TrentinoAlto Adige, Italy


2003

Abdus Salam International Centre for Theoretical Physics
Trst, Friuli Venezia Giulia, Italy


2002

Princeton University
 Department of Chemical and Biological Engineering
Princeton, New Jersey, United States 
University of New Mexico
 Department of Physics & Astronomy
Albuquerque, New Mexico, United States


2001

Rensselaer Polytechnic Institute
 Department of Mathematical Sciences
Троя, New York, United States


2000

Xerox Research Center Webster
Webster, New York, United States 
City College of New York
 Department of Physics
New York, New York, United States


19941998

University Carlos III de Madrid
 High Technical College
Getafe, Madrid, Spain 
Tel Aviv University
 Department of Applied Mathematics
Tell Afif, Tel Aviv, Israel


19931998

University of Bayreuth
 Institute of Physics
Bayreuth, Bavaria, Germany 
Institute of Physics, Zagreb
Zagrabia, Grad Zagreb, Croatia


1997

Fudan University
 Department of Physics
Shanghai, Shanghai Shi, China 
University of Rome Tor Vergata
 Dipartimento di Fisica
Roma, Latium, Italy 
Ukrainian Academy of Agrarian Sciences
Kievo, Kyiv City, Ukraine


1996

Universidad Autónoma de San Luis Potosí
 Instituto de Física
San Luis, San Luis Potosí, Mexico


1995

University of Hyderabad
Bhaganagar, Telangana, India


1992

Scuola Internazionale Superiore di Studi Avanzati di Trieste
Trst, Friuli Venezia Giulia, Italy


1990

Kansas State University
 Department of Physics
Манхэттен, Kansas, United States 
The Ohio State University
 Department of Mathematics
Columbus, Ohio, United States


1986

Fukuoka Institute of Technology
Hukuoka, Fukuoka, Japan


1981

Wake Forest University
 Department of Physics
WinstonSalem, North Carolina, United States


19791980

Queen Mary, University of London
Londinium, England, United Kingdom


19751978

Cornell University
 Laboratory of Atomic and Solid State Physics
Ithaca, NY, United States 
University of Pennsylvania
Filadelfia, Pennsylvania, United States
