Prokof'ev, Nikolai
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Professor, Physics Department
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Prokof'ev
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Nikolai
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Physics
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Publication Open Access Critical Temperature Curve in BEC-BCS Crossover(2008-01) Burovski, E; Kozik, E; Prokof'ev, N; Svistunov, B; Troyer, MThe strongly correlated regime of the crossover from Bardeen-Cooper-Schrieffer pairing to Bose-Einstein condensation can be realized by diluting a system of two-component fermions with a short-range attractive interaction. We investigate this system via a novel continuous-space-time diagrammatic determinant Monte Carlo method and determine the universal curve Tc/εF for the transition temperature between the normal and the superfluid states as a function of the scattering length with the maximum on the Bose-Einstein condensation side. At unitarity, we confirm that Tc/εF=0.152(7).Publication Open Access Comment on “Hausdorff Dimension of Critical Fluctuations in Abelian Gauge Theories”(2006-01) Prokof'ev, N; Svistunov, BA Comment on the Letter by J. Hove, S. Mo, and A. Sudbø Phys. Rev. Lett. 85, 2368 (2000). The authors of the Letter offer a Reply.Publication Open Access Spin bath-mediated decoherence in superconductors(2000-01) Prokof'ev, Nikolai; Stamp, P.C.EWe consider a SQUID tunneling between 2 nearly degenerate flux states. Decoherence caused by paramagnetic and nuclear spins in the low-T limit is shown to be much stronger than that from electronic excitations. The decoherence time ô is determined by the linewidth Eo of spin bath states, which can be reduced by a correct choice of ring geometry and isotopic purification. Eo can be measured in either field sweep or microwave absorption experiments, allowing both a test of the theory and design control.Publication Open Access Comment on “Phase Diagram of a Disordered Boson Hubbard Model in Two Dimensions”(2003-01) Prokof’ev, N; Svistunov, BIn a recent Letter [1] (see also [2]) the authors presented numerical evidence supporting an idea of a direct transition between the superfluid (SF) and Mott insulating (MI) phases in the disordered Bosonic system, and even studied non-trivial properties of the multicritical line where SF, MI and the Bose Glass (BG) phases meet. The results were obtained from Monte Carlo simulations of the (2+1)-dimensional classical loop-current model [3] with the lattice action S = 1 2K Þ E ~ J=0 XrƒÑ ~ J2(r, ƒÑ) . 2(ƒÊ + v(r)) ~ JƒÑ (r, ƒÑ) . (1) where r, ƒÑ are spatial and imaginary time coordinates, and ~ J(r, ƒÑ) are integer current vectors with zero divergence. The spatial disorder potential v(r) is uniformly distributed on the interval (.,).Publication Open Access Self-trapping of polarons in the Rashba-Pekar model(2002-01) Mishchenko, A; Nagaosa, N; Prokof'ev, Nikolai; Sakamoto, A; Svistunov, BWe performed a quantum Monte Carlo study of the exciton-polaron model which features the self-trapping phenomenon when the coupling strength and/or particle momentum is varied. Accurate data for energy, effective mass, the structure of the polaronic cloud, dispersion law, and spectral function became available throughout the crossover region. We observed that self-trapping cannot be reduced to hybridization of two states with different lattice deformation, and that at least three states are involved in the crossover from light- to heavy-mass regimes.Publication Open Access Diagrammatic Quantum Monte Carlo for Two-Body Problems: Applied to Excitons(2001-01) Burovski, E; Mishchenko, A; Prokof'ev, Nikolai; Svistunov, BWe present a novel method for the precise numeric solution of the irreducible two-body problem and apply it to excitons in solids. The approach is based on the Monte Carlo simulation of the two-body Green function specified by Feynman’s diagrammatic expansion. Our method does not rely on the specific form of the electron and hole dispersion laws and is valid for any attractive electron-hole potential. We establish limits of validity of the Wannier (large radius) and Frenkel (small radius) approximations, present accurate data for the intermediate radius excitons, and give evidence for the charge transfer nature of the monopolar exciton in mixed valence materials.Publication Open Access Comprehensive study of Fröhlich polaron(2000-01) Mishchenko, A; Prokof'ev, N; Svistunov, B; Sakamoto, AA study of the Fröhlich polaron model is performed on the basis of diagrammatic quantum Monte Carlo technique which is enhanced by novel method of spectral analysis of the polaron Green function. We make available for the first time precise data for the effective mass, including the region of intermediate and strong couplings, and analyze the structure of the polaron cloud. A non-trivial structure of the spectral density is observed: at high enough couplings the spectral continuum features pronounced peaks that we attribute to unstable excited states of the polaron.Publication Open Access Weakly Interacting Bose Gas in the Vicinity of the Critical Point(2004-01) Prokof'ev, Nikolai; Ruebenacker, O; Svistunov, BorisWe consider a three-dimensional weakly interacting Bose gas in the fluctuation region (and its vicinity) of the normal-superfluid phase transition point. We establish relations between basic thermodynamic functions: density, n(T, ì), superfluid density ns(T, ì), and condensate density, ncnd(T, ì). Being universal for all weakly interacting |ø|4 systems, these relations are obtained from Monte Carlo simulations of the classical |ø|4 model on a lattice. Comparing with the mean-field results yields a quantitative estimate of the fluctuation region size. Away from the fluctuation region, on the superfluid side, all the data perfectly agree with the predictions of the quasicondensate mean field theory.—This demonstrates that the only effect of the leading above-the-mean-field corrections in the condensate based treatments is to replace the condensate density with the quasicondensate one in all local thermodynamic relations. Surprisingly, we find that a significant fraction of the density profile of a loosely trapped atomic gas might correspond to the fluctuation region.Publication Open Access Local Stress and Superfluid Properties of Solid 4He(2008-01) Pollet, L; Boninsegni, M; Kuklov, A; Prokof'ev, Nikolai; Svistunov, Boris; Troyer, MWe provide a semiquantitative tool, derived from first-principles simulations, for answering the question of whether certain types of defects in solid 4He support mass superflow. Although ideal crystals of 4He are not supersolid, the gap for vacancy creation closes when applying a moderate stress. While a homogeneous system becomes unstable at this point, the stressed core of crystalline defects (dislocations and grain boundaries) can turn superfluid.Publication Open Access Collective dynamics of interacting Ising spins: Exact results for the Bethe lattice(2009-01) Burin, A; Prokof'ev, N; Tupitsyn, IWe study the low temperature dynamics in films made of molecular magnets, i. e. crystals composed of molecules having large electronic spin S in their ground state. The electronic spin dynamics is mediated by coupling to a nuclear spin bath; this coupling allows transitions for a small fraction of electronic spins between their two energy minima, Sz = ±S, under resonant conditions when the change of the Zeeman energy in magnetic dipolar field of other electronic spins is compensated by interaction with nuclear spins. Transitions of resonant spins can result in opening or closing resonances in their neighbors leading to the collective dynamics at sufficiently large density P0 of resonant spins. We formulate and solve the equivalent dynamic percolation problem for the Bethe lattice (BL) of spins interacting with z neighbors and find that depending on the density of resonant spins P0 and the number of neighbors z the system has either one (2 < z < 6) or two (z 6) kinetic transitions at P0 = Pc1 e-1/3/(3z) and P0 = Pc2 e-1/z. The former transition is continuous and associated with the formation of an infinite cluster of coupled resonant spins similarly to the static percolation transition occurring at P0 1/z. The latter transition, z > 5, is discontinuous and associated with the instantaneous increase in the density of resonant spins from the small value 1/z to near unity. Experimental implications of our results are discussed.