Advances in creating stable dipolar Bose systems and ingenious box traps have generated great interest in the field of cold bosons. Theory study of dipolar bosons at finite temperature $T$ has been limited. We study two-dimensional dipolar bosons at arbitrary tilt angle $\ensuremath{\theta}$ using finite- $T$ random phase approximation. We show that a comprehensive understanding of phases and instabilities at nonzero $T$ can be obtained by concurrently considering dipole strength, density, temperature, and $\ensuremath{\theta}$. We find the system to be in a homogeneous noncondensed phase that undergoes a collapse transition at large $\ensuremath{\theta}$, and a finite momentum instability, signaling a striped phase, at large dipolar strength; there are important differences from the $T=0$ case. As $T\ensuremath{\rightarrow}0$, a Bose-condensed phase appears at critical dipolar strength, and at critical density. Our predictions for a polar molecule system, $^{41}\mathrm{K}^{87}\mathrm{Rb}$ , and $^{166}\mathrm{Er}$ may provide tests of our results.Advances in creating stable dipolar Bose systems and ingenious box traps have generated great interest in the field of cold bosons. Theory study of dipolar bosons at finite temperature $T$ has been limited. We study two-dimensional dipolar bosons at arbitrary tilt angle $\ensuremath{\theta}$ using finite-$T$ random phase approximation. We show that a comprehensive understanding of phases and instabilities at nonzero $T$ can be obtained by concurrently considering dipole strength, density, temperature, and $\ensuremath{\theta}$. We find the system to be in a homogeneous noncondensed phase that undergoes a collapse transition at large $\ensuremath{\theta}$, and a finite momentum instability, signaling a striped phase, at large dipolar strength; there are important differences from the $T=0$ case. As $T\ensuremath{\rightarrow}0$, a Bose-condensed phase appears at critical dipolar strength, and at critical density. Our predictions for a polar molecule system, $^{41}\mathrm{K}^{87}\mathrm{Rb}$, and $^{166}\mathrm{Er}$ may provide tests of our results.

arXiv:2012.04244Physical Review AApr 12, 20212 citations

2D Dipolar Bosons with Non-zero Tilt Angles

Pengtao Shen, Khandker Quader

Recent experimental advances in creating stable dipolar systems, including polar molecules with large electric dipole moments, have led to vigorous theoretical activities. Here we discuss our work on homogeneous 2D dipolar bosons with dipoles oriented at an angle to the direction perpendicular to the confining 2D plane, i.e. for non-zero tilt angles. Using Bogoliubov-de Gennes equations, we obtain T=0 excitation spectrum of the dipolar Bose gas, and explore instabilities at varying tilt angle, density and dipolar coupling. We map out a phase diagram a function of tilt angle, dipole strength and density. We find the development of maxon-roton behavior leading to roton instabilities at large densities for small tilt angles, and at low densities for large tilt angles. The behavior is anisotropic in k-space; accordingly the roton instabilities occur in the k y direction, suggestive of inhomogeneity and stripe phase, with density mode becoming soft in the y direction. Our results compare favorably with existing Quantum Monte Carlo calculations for non-zero tilt angles.Recent experimental advances in creating stable dipolar systems, including polar molecules with large electric dipole moments, have led to vigorous theoretical activities. Here we discuss our work on homogeneous 2D dipolar bosons with dipoles oriented at an angle to the direction perpendicular to the confining 2D plane, i.e. for non-zero tilt angles. Using Bogoliubov-de Gennes equations, we obtain T=0 excitation spectrum of the dipolar Bose gas, and explore instabilities at varying tilt angle, density and dipolar coupling. We map out a phase diagram a function of tilt angle, dipole strength and density. We find the development of maxon-roton behavior leading to roton instabilities at large densities for small tilt angles, and at low densities for large tilt angles. The behavior is anisotropic in k-space; accordingly the roton instabilities occur in the k y direction, suggestive of inhomogeneity and stripe phase, with density mode becoming soft in the y direction. Our results compare favorably with existing Quantum Monte Carlo calculations for non-zero tilt angles.

Journal of Physics Conference SeriesJun 1, 20184 citations

Advances in creating stable dipolar Bose systems and ingenious box traps have generated great interest in the field of cold bosons. Theory study of dipolar bosons at finite temperature

T

has been limited. We study two-dimensional dipolar bosons at arbitrary tilt angle $\ensuremath{\theta}$ using finite-

T

random phase approximation. We show that a comprehensive understanding of phases and instabilities at nonzero

T

can be obtained by concurrently considering dipole strength, density, temperature, and $\ensuremath{\theta}$. We find the system to be in a homogeneous noncondensed phase that undergoes a collapse transition at large $\ensuremath{\theta}$, and a finite momentum instability, signaling a striped phase, at large dipolar strength; there are important differences from the

T=0

case. As $T\ensuremath{\rightarrow}0$, a Bose-condensed phase appears at critical dipolar strength, and at critical density. Our predictions for a polar molecule system,

^{41}\mathrm{K}^{87}\mathrm{Rb}

, and

^{166}\mathrm{Er}

may provide tests of our results.