Coupled motion of Xe clusters and quantum vortices in He nanodroplets

Jones, Curtis F.; Bernando, Charles; Tanyag, Rico Mayro P.; Bacellar, Camila; Ferguson, Ken; Gomez, Luis F.; Anielski, Denis; Belkacem, A.; Boll, Rebecca; Bozek, John D.; Carron, S.; Cryan, James; Englert, Lars; Epp, Sascha W.; Erk, Benjamin; Foucar, L.; Hartmann, R.; Neumark, Daniel M.; Rolles, Daniel; Rudenko, Artem; Siefermann, Katrin R.; Weise, Fabian; Rudek, Benedikt; Sturm, Felix; Ullrich, J.; Bostedt, Christoph; Geßner, Oliver; Vilesov, Andrey F.

doi:10.1103/physrevb.93.180510

Cited by 34 publications

(45 citation statements)

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“…X-ray diffraction imaging of Xe doped He droplets revealed Bragg spots, confirming the existence of quantum vortex lattices that led to the condensation of 100-200 Xe clusters in a periodic array [18]. Positions and shapes of individual vortices could be deduced from diffraction images without Bragg spots by using a recently developed phase retrieval algorithm [19][20]. It was also found that about 50% of the droplets produce anisotropic diffraction patterns that can be described by concentric elliptic rings.…”

Section: Introductionmentioning

confidence: 79%

Shapes of rotating superfluid helium nanodroplets

et al. 2017

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Rotating superfluid He droplets of approximately 1 μm in diameter were obtained in a free nozzle beam expansion of liquid He in vacuum and were studied by single-shot coherent diffractive imaging using an x-ray free electron laser. The formation of strongly deformed droplets is evidenced by large anisotropies and intensity anomalies (streaks) in the obtained diffraction images. The analysis of the images shows that, in addition to previously described axially symmetric oblate shapes, some droplets exhibit prolate shapes. Forward modeling of the diffraction images indicates that the shapes of rotating superfluid droplets are very similar to their classical counterparts, giving direct access to the droplet angular momenta and angular velocities. The analyses of the radial intensity distribution and appearance statistics of the anisotropic images confirm the existence of oblate metastable superfluid droplets with large angular momenta beyond the classical bifurcation threshold.3

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Section: Introductionmentioning

confidence: 79%

Shapes of rotating superfluid helium nanodroplets

et al. 2017

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“…Angulons, on the other hand, are the eigenstates of the total angular momentum operator,L 2 , and therefore the transferred angular momentum is three-dimensional. While vortex instabilities have been subject to several experimental studies in the context of superfluid helium [4,5,[26][27][28][29][30][31], ultracold quantum gases [32][33][34][35][36], and superconductors [37][38][39][40], the transfer of angular momentum to a superfluid via the angulon instabilities has not yet been observed in experiment.In this Letter we provide evidence for the emergence of the angulon instabilities in experiments on CH 3 [41] and NH 3 [42] molecules trapped in superfluid helium nanodroplets. Spectroscopy of molecules matrix-isolated in 4 He has been an active area of research during the last two decades [6][7][8][9][10][11][12][13]43].…”

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confidence: 99%

Fingerprints of angulon instabilities in the spectra of matrix-isolated molecules

Cherepanov

Lemeshko

2017

Phys. Rev. Materials

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The formation of vortices is usually considered to be the main mechanism of angular momentum disposal in superfluids. Recently, it was predicted that a superfluid can acquire angular momentum via an alternative, microscopic route -namely, through interaction with rotating impurities, forming so-called 'angulon quasiparticles ' [Phys. Rev. Lett. 114, 203001 (2015)]. The angulon instabilities correspond to transfer of a small number of angular momentum quanta from the impurity to the superfluid, as opposed to vortex instabilities, where angular momentum is quantized in units of per atom. Furthermore, since conventional impurities (such as molecules) represent three-dimensional (3D) rotors, the angular momentum transferred is intrinsically 3D as well, as opposed to a merely planar rotation which is inherent to vortices. Herein we show that the angulon theory can explain the anomalous broadening of the spectroscopic lines observed for CH3 and NH3 molecules in superfluid helium nanodroplets, thereby providing a fingerprint of the emerging angulon instabilities in experiment.One of the distinct features of the superfluid phase is the formation of vortices -topological defects carrying quantized angular momentum, which arise if the bulk of the superfluid rotates faster than some critical angular velocity [1,2]. Vortex nucleation has been considered to be the main mechanism angular momentum disposal in superfluids [1][2][3][4][5]. Recently, it was predicted that a superfluid can acquire angular momentum via a different, microscopic route, which takes effect in the presence of rotating impurities, such as molecules [6][7][8][9][10][11][12][13]. In particular, it was demonstrated that a rotating impurity immersed in a superfluid forms the 'angulon' quasiparticle, which can be thought of as a rigid rotor dressed by a cloud of superfluid excitations carrying angular momentum [14-21].The angulon theory was able to describe, in good agreement with experiment, renormalization of rotational constants [22,23] and laser-induced dynamics [24,25] of molecules in superfluid helium nanodroplets. One of the key predictions of the angulon theory are the socalled 'angulon instabilities ' [14-16] that occur at some critical value of the molecule-superfluid coupling where the angulon quasiparticle becomes unstable and one or a few quanta of angular momentum are resonantly transferred from the impurity to the superfluid. These instabilities are fundamentally different from the vortex instabilities, associated with the transfer of angular momentum quantised in units of per atom of the superfluid. Furthermore, vortices can be thought of as planar rotors, i.e., the eigenstates of theL z operator. Angulons, on the other hand, are the eigenstates of the total angular momentum operator,L 2 , and therefore the transferred angular momentum is three-dimensional. While vortex instabilities have been subject to several experimental studies in the context of superfluid helium [4,5,[26][27][28][29][30][31], ultracold quantum gases [32][33][34][35][36]...

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“…The coupled motion of a vortex-dopant complex and decoupling conditions are studied. The reconnection of vortices, taken as an example of a fundamental process responsible for the evolution of a quantum turbulent state, is modeled to illustrate the difference between the light and heavy doping cases.Illuminating experiments in quantum turbulence were performed recently using superfluid helium nanodroplets [13][14][15][16]. Vortex filaments in rotating droplets were doped with Ag and Xe atoms and studied using a femtosecond x-ray coherent diffractive imaging technique as well as electron microscopy preceded by surfacedeposition of the samples.…”

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confidence: 99%

“…Several questions were raised in these works, including the origin of unusual shapes of doped helium droplets and distribution of vortices inside the droplet. Although certain aspects were clarified by theorists [17][18][19], the connection between the rotational motion of a droplet and a dopant still remains unclear [16]. In nanodroplet experiments doping particles are approximately 33 times heavier than fluid atoms and the diameter of each particle is comparable with a vortex core size in helium.…”

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Static and dynamic properties of heavily doped quantum vortices

Pshenichnyuk

2017

New J. Phys.

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Quantum vortices in superfluids may capture matter and deposit it inside their core. By doping vortices with foreign particles one can effectively visualize them and study them experimentally. To acquire a better understanding of the interaction between quantum vortices and matter, and clarify the details of recent experiments, the properties of doped vortices are investigated here theoretically in the regimes where the doping mass becomes close to the total mass of superfluid particles forming a vortex. Such formations are dynamically stable and, possessing both vorticity and enhanced inertia, demonstrate properties that are different from the pure vortex case. The goal of this paper is to define and investigate the universal aspects of heavily doped vortex behavior, which can be realized in different types of quantum mixtures. The proposed 3D model is based on a system of coupled semiclassical matter wave equations that are solved numerically in a wide range of physical parameters. The size, geometry and binding energy of dopants in different regimes are discussed. The coupled motion of a vortex-dopant complex and decoupling conditions are studied. The reconnection of vortices, taken as an example of a fundamental process responsible for the evolution of a quantum turbulent state, is modeled to illustrate the difference between the light and heavy doping cases.Illuminating experiments in quantum turbulence were performed recently using superfluid helium nanodroplets [13][14][15][16]. Vortex filaments in rotating droplets were doped with Ag and Xe atoms and studied using a femtosecond x-ray coherent diffractive imaging technique as well as electron microscopy preceded by surfacedeposition of the samples. Several questions were raised in these works, including the origin of unusual shapes of doped helium droplets and distribution of vortices inside the droplet. Although certain aspects were clarified by theorists [17][18][19], the connection between the rotational motion of a droplet and a dopant still remains unclear [16]. In nanodroplet experiments doping particles are approximately 33 times heavier than fluid atoms and the diameter of each particle is comparable with a vortex core size in helium. This is quite opposite, for instance, in comparison to large and light electron bubbles often used as dopants and well studied in the past both experimentally and theoretically [20][21][22]. Being captured, heavy particles may influence the vortex motion significantly and theoretical modeling is necessary to understand the details of their behavior.According to the results of Gordon and colleagues [8,9], guest atoms in helium above a critical temperature tend to form spherical clusters. In superfluid helium below critical temperature impurities with a certain probability stick together to produce long cylindrical filaments, which are attributed to the presence of quantum vortices. These filaments are stable enough to exist independently, by decoupling from vortices, which allows them to be studied using a surface-depo...

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Coupled motion of Xe clusters and quantum vortices in He nanodroplets

Cited by 34 publications

References 34 publications

Shapes of rotating superfluid helium nanodroplets

Shapes of rotating superfluid helium nanodroplets

Fingerprints of angulon instabilities in the spectra of matrix-isolated molecules

Static and dynamic properties of heavily doped quantum vortices

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