arXiv subjects

Boris V. Svistunov

Publications and source records attributed to Boris V. Svistunov.

24 records · Page 2Linked to original sources

arXiv2014

Asymptotically Exact Scenario of Strong-Disorder Criticality in One-Dimensional Superfluids

We present a controlled rare-weak-link theory of the superfluid-to-Bose/Mott glass transition in one-dimensional disordered systems. The transition has Kosterlitz-Thouless critical properties but may occur at an arbitrary large value of the Luttinger parameter $K$. In contrast to the scenario by Altman {\it et al.} [Phys. Rev. B {\bf 81}, 174528 (2010)], the hydrodynamic description is valid under the correlation radius and defines criticality via the renormalization of microscopically weak links, along the lines of Kane and Fisher [Phys. Rev. Lett. {\bf 68}, 1220 (1992)]. The hallmark of the theory is the relation $K^{(c)}=1/ζ$ between the critical value of the Luttinger parameter at macroscopic scales and the microscopic (irrenormalizable) exponent $ζ$ describing the scaling $\propto 1/N^{1-ζ}$ for the strength of the weakest link among the $N/L \gg 1$ disorder realizations in a system of fixed mesoscopic size $L$.

cond-mat.stat-mech↗

arXiv2011

Phase Diagram of Commensurate Two-Dimensional Disordered Bose Hubbard Model

We establish the full groundstate phase diagram of disordered Bose-Hubbard model in two-dimensions at unity filling factor via quantum Monte Carlo simulations. Similarly to the three-dimensional case we observe extended superfluid regions persisting up to extremely large values of disorder and interaction strength which, however, have small superfluid fractions and thus low transition temperatures. In the vicinity of the superfluid--insulator transition of the pure system, we observe an unexpectedly weak---almost not resolvable---sensitivity of the critical interaction to the strength of (weak) disorder.

cond-mat.other↗

arXiv2010

Regularization of Diagrammatic Series with Zero Convergence Radius

The divergence of perturbative expansions for the vast majority of macroscopic systems, which follows from Dyson's collapse argument, prevents Feynman's diagrammatic technique from being directly used for controllable studies of strongly interacting systems. We show how the problem of divergence can be solved by replacing the original model with a convergent sequence of successive approximations which have a convergent perturbative series. As a prototypical model, we consider the zero-dimensional $\vert ψ\vert^4$ theory.

cond-mat.stat-mech↗

arXiv2001

Scenario of strongly non-equilibrium Bose-Einstein condensation

Large scale numerical simulations of the Gross-Pitaevskii equation are used to elucidate the self-evolution of a Bose gas from a strongly non-equilibrium initial state. The stages of the process confirm and refine the theoretical scenario of Bose-Einstein condensation developed by Svistunov, Kagan, and Shlyapnikov [1-3]: the system evolves from the regime of weak turbulence to superfluid turbulence, via states of strong turbulence in the long-wavelength region of energy space.

cond-mat.soft↗

arXiv1998

Polaron Problem by Diagrammatic Quantum Monte Carlo

We present a precise solution of the polaron problem by a novel Monte Carlo method. Basing on conventional diagrammatic expansion for the Green function of the polaron, $G({\bf k}, τ)$, we construct a process of generating continuous random variables ${\bf k}$ and $τ$, with the distribution function exactly coinciding with $G({\bf k}, τ)$. The polaron spectrum is extracted from the asymptotic behavior of the Green function. We compare our results for the polaron energy with the variational treatment of Feynman, and for the first time present precise dispersion curve which features an ending point at finite momentum.

cond-mat↗

arXiv1996

Superfluid - Bose-Glass Transition in Weakly Disordered Commensurate One-Dimensional System

We study the effect of commensurability (integer filling factor) on the superfluid (SF) - Bose-glass (BG) transition in a one-dimensional disordered system in the limit of weak disorder, when the effect is most pronounced and, on the other hand, may be traced via the renormalization-group analysis. The equation for the SF-BG phase boundary demonstrating the effect of disorder-stimulated superfluidity implies that the strength of disorder sufficient to restore superfluidity from Mott insulator (MI) is much larger than that enough to turn MI into BG. Thus we provide an explicit proof of the fact that at arbitrarily small disorder the SF and MI phases are always separated by BG.

cond-mat↗