We study the superfluid properties of a system of fully polarized dipolar bosons moving in the XY plane. We focus on the general case where the polarization field forms an arbitrary angle α with respect to the Z axis, while the system is still stable. We use the diffusion Monte Carlo and the path integral ground state methods to evaluate the one-body density matrix and the superfluid fractions in the region of the phase diagram where the system forms stripes. Despite its oscillatory behavior, the presence of a finite large-distance asymptotic value in the s-wave component of the one-body density matrix indicates the existence of a Bose condensate. The superfluid fraction along the stripes direction is always close to 1, while in the Y direction decreases to a small value that is nevertheless different from zero. These two facts confirm that the stripe phase of the dipolar Bose system is a clear candidate for an intrinsic supersolid without the presence of defects as described by the Andreev-Lifshitz mechanism.We study the superfluid properties of a system of fully polarized dipolar bosons moving in the XY plane. We focus on the general case where the polarization field forms an arbitrary angle α with respect to the Z axis, while the system is still stable. We use the diffusion Monte Carlo and the path integral ground state methods to evaluate the one-body density matrix and the superfluid fractions in the region of the phase diagram where the system forms stripes. Despite its oscillatory behavior, the presence of a finite large-distance asymptotic value in the s-wave component of the one-body density matrix indicates the existence of a Bose condensate. The superfluid fraction along the stripes direction is always close to 1, while in the Y direction decreases to a small value that is nevertheless different from zero. These two facts confirm that the stripe phase of the dipolar Bose system is a clear candidate for an intrinsic supersolid without the presence of defects as described by the Andreev-Lifshitz mechanism.

arXiv:1708.07673Physical Review LettersDec 20, 201770 citations

Condensate fraction of cold gases in a nonuniform external potential

G. E. Astrakharchik, Konstantin V. Krutitsky

Exact calculation of the condensate fraction in multidimensional inhomogeneous interacting Bose systems in a confining potential of arbitrary shape is a difficult computational problem. We have developed an iterative procedure which allows us to calculate the condensate fraction as well as the corresponding eigenfunction of the one-body density matrix. We successfully validate this procedure in diffusion Monte Carlo simulations of a Bose gas in an optical lattice at zero temperature. We also discuss the relation between different criteria used for testing coherence in cold Bose systems, such as the fraction of particles that are superfluid, condensed, or in the zero-momentum state.Exact calculation of the condensate fraction in multidimensional inhomogeneous interacting Bose systems in a confining potential of arbitrary shape is a difficult computational problem. We have developed an iterative procedure which allows us to calculate the condensate fraction as well as the corresponding eigenfunction of the one-body density matrix. We successfully validate this procedure in diffusion Monte Carlo simulations of a Bose gas in an optical lattice at zero temperature. We also discuss the relation between different criteria used for testing coherence in cold Bose systems, such as the fraction of particles that are superfluid, condensed, or in the zero-momentum state.

arXiv:1102.3565Physical Review ASep 22, 201114 citations

ON THE THEORY OF SUPERFLUIDITY

Nikolay N. Bogolubov

Elsevier eBooksJan 1, 197152 citations

On the theory of superfluidity

Yongle Yu

arXiv:cond-mat/0609711Annals of PhysicsJul 11, 20087 citations

Condensate and superfluid fractions for varying interactions and temperature

Vyacheslav I. Yukalov, Elizaveta P. Yukalova

A system with Bose-Einstein condensate is considered in the frame of the self-consistent mean-field approximation, which is conserving, gapless, and applicable for arbitrary interaction strengths and temperatures. The main attention is paid to the thorough analysis of the condensate and superfluid fractions in the whole range of the interaction strength, between zero and infinity, and for all temperatures between zero and the critical point ${T}_{c}$ . The normal and the anomalous averages are shown to be of the same order for almost all interactions and temperatures, except the close vicinity of ${T}_{c}$ . But even in the vicinity of the critical temperature, the anomalous average cannot be neglected, since only in the presence of the latter the phase transition at ${T}_{c}$ becomes of second order, as it should be. Increasing temperature influences the condensate and superfluid fractions in a similar way, by diminishing them; but their behavior with respect to the interaction strength is very different. For all temperatures, the superfluid fraction is larger than the condensate fraction. These coincide only at ${T}_{c}$ or under zero interactions. For asymptotically strong interactions, the condensate is almost completely depleted, even at low temperatures, while the superfluid fraction can be close to one.A system with Bose-Einstein condensate is considered in the frame of the self-consistent mean-field approximation, which is conserving, gapless, and applicable for arbitrary interaction strengths and temperatures. The main attention is paid to the thorough analysis of the condensate and superfluid fractions in the whole range of the interaction strength, between zero and infinity, and for all temperatures between zero and the critical point ${T}_{c}$. The normal and the anomalous averages are shown to be of the same order for almost all interactions and temperatures, except the close vicinity of ${T}_{c}$. But even in the vicinity of the critical temperature, the anomalous average cannot be neglected, since only in the presence of the latter the phase transition at ${T}_{c}$ becomes of second order, as it should be. Increasing temperature influences the condensate and superfluid fractions in a similar way, by diminishing them; but their behavior with respect to the interaction strength is very different. For all temperatures, the superfluid fraction is larger than the condensate fraction. These coincide only at ${T}_{c}$ or under zero interactions. For asymptotically strong interactions, the condensate is almost completely depleted, even at low temperatures, while the superfluid fraction can be close to one.

arXiv:0707.1233Physical Review AJul 2, 200733 citations

{T}_{c}

. The normal and the anomalous averages are shown to be of the same order for almost all interactions and temperatures, except the close vicinity of

{T}_{c}

. But even in the vicinity of the critical temperature, the anomalous average cannot be neglected, since only in the presence of the latter the phase transition at

{T}_{c}

becomes of second order, as it should be. Increasing temperature influences the condensate and superfluid fractions in a similar way, by diminishing them; but their behavior with respect to the interaction strength is very different. For all temperatures, the superfluid fraction is larger than the condensate fraction. These coincide only at

{T}_{c}

or under zero interactions. For asymptotically strong interactions, the condensate is almost completely depleted, even at low temperatures, while the superfluid fraction can be close to one.