Charge Correlations in a Harmonic Trap

J. Phys. D: Appl. Phys.

et al. 2014

Lasers have been used extensively to manipulate matter in a controlled way -from single atoms and molecules up to macroscopic materials. They are particularly valuable for the analysis and control of mesoscopic systems such as few-particle clusters. Here we report on recent work on finite size complex (dusty) plasma systems. These are unusual types of clusters with very strong inter-particle interaction so that, at room temperature, they are practically in their ground state. Lasers are employed as a tool to achieve excited states and phase transitions.The most attractive feature of dusty plasmas is that they allow for a precise diagnostic with single-particle resolution. From such measurements, the structural properties of finite two-dimensional (2D) clusters and three-dimensional (3D) spherical crystals in nearly harmonic traps-so-called Yukawa balls-have been explored in great detail. Their structural features-the shell compositions and the order within the shells-have been investigated and good agreement to theoretical predictions was found. Open questions on the agenda are the excitation behavior, the structural changes, and phase transitions that occur at elevated temperature.Here we report on recent experimental results where laser heating methods were further improved and applied to finite 2D and 3D dust clusters. Comparing to simulations, we demonstrate that laser heating indeed allows to increase the temperature in a controlled manner. For the analysis of thermodynamic properties and phase transitions in these finite systems, we present theoretical and experimental results on the basis of the instantaneous normal modes, pair distribution function and the recently introduced center-two-particle correlation function.arXiv:1402.7182v2 [physics.plasm-ph] 7 Jul 2014 ‡ Strictly, the definition (1) is an appropriate measure for the potential energy only when the pair interaction is Coulombic. In the case of screening, the effective coupling parameter depends on the screening length λ D [7]. For the results reported in this paper, the dust-dust interaction is moderately screened and the definition (1) is sufficiently accurate.

Section: Structural Properties Of Finite Dust Clustersmentioning

confidence: 99%

Controlling strongly correlated dust clusters with lasers

Thomsen

Ludwig

J. Phys. D: Appl. Phys.

et al. 2014

“…These data allows for a precise assessment of the coupling strength of experiments and simulations via a structural measurement and give a benchmark for analytical models.Strongly coupled plasmas-in which the interaction energy exceeds the thermal energy-are often modeled as one-component plasmas (OCP, e.g., Ref.[1]) which include pure Coulomb systems and screened Yukawa systems. These models are relevant for dusty or complex plasmas [2,3], ultracold neutral plasmas [4], ions in traps [5,6], warm dense matter [7,8], and colloidal suspensions [3]. One of the primary appeals of the OCP is its simplicity.…”

mentioning

confidence: 99%

“…[1]) which include pure Coulomb systems and screened Yukawa systems. These models are relevant for dusty or complex plasmas [2,3], ultracold neutral plasmas [4], ions in traps [5,6], warm dense matter [7,8], and colloidal suspensions [3]. One of the primary appeals of the OCP is its simplicity.…”

mentioning

confidence: 99%

First‐Principle Results for the Radial Pair Distribution Function in Strongly Coupled One‐Component Plasmas

Ott

2014

Contrib. Plasma Phys.

Self Cite

The radial pair distribution function (RPDF) is the most simple way to characterize the structure of a system. In this work, we provide a comprehensive overview of the dependence of the RPDF on the coupling parameter and screening length in Coulomb and Yukawa One-Component plasmas. These data allows for a precise assessment of the coupling strength of experiments and simulations via a structural measurement and give a benchmark for analytical models.Strongly coupled plasmas-in which the interaction energy exceeds the thermal energy-are often modeled as one-component plasmas (OCP, e.g., Ref.[1]) which include pure Coulomb systems and screened Yukawa systems. These models are relevant for dusty or complex plasmas [2, 3], ultracold neutral plasmas [4], ions in traps [5,6], warm dense matter [7,8], and colloidal suspensions [3]. One of the primary appeals of the OCP is its simplicity. Only one parameter [besides the screening length in the case of Yukawa systems], Γ = Q 2 /(ak B T ) (where a is the Wigner-Seitz radius and T the temperature), suffices to characterize the system completely and determines all thermodynamic properties. The coupling strength Γ has a straightforward interpretation as the ratio of the nearest-neighbor Coulomb interaction energy Q 2 /a to the typical thermal energy k B T of one particle. Many fields are interested in the liquid strong-coupling regime, roughly defined by 1 Γ Γ c , where the crystallization point Γ c is on the order of 100 and depends on the dimensionality and the screening [9, 10]. Knowledge of Γ is, therefore, of paramount importance for a reliable modeling of a given experimental system. It can, however, be difficult to assess experimentally, since it requires separate measurements of the temperature T , the charge state Q, and the number density n = [(4π/3)a 3 ] −1 (n = [πa 2 ] −1 for 2D).We have, therefore, recently presented a very general method to assess the coupling strength of a threedimensional Coulomb and Yukawa system [11], extending an analogous previous work for two-dimensional systems [12]. In this method, the coupling strength is extracted from structural information alone, without the need to measure the charge state or the temperature. 1 It is based on the observation that the height g max of the first peak of the radial pair distribution function (RPDF) uniquely corresponds to the coupling strength of a system if the interaction potential is known. In the case of one-component plasmas, this requires knowledge of the inverse screening length κ, which then, together with Γ known from g max , uniquely defines all thermodynamic properties of the system. 2 In this contribution, we provide additional numerical data on seven characteristics of the RPDF (see inset in Fig. 1). This substantially extends our previous works [11,12] that were based on the nearest-neighbor distribution alone, and allows for a more detailed comparison with experimental results for the RPDF that are accessible, e.g., in dusty plasmas or colloidal suspensions. This potentially increases th...

“…39. Since the 12 The results were kindly provided by Hauke Thomsen [126]. The simulations were performed with the Metropolis algorithm and parallel tempering.…”

Section: Discussion Of the 1d Resultsmentioning

confidence: 99%

Quantum Breathing Mode of Trapped Particles: From Nanoplasmas to Ultracold Gases

Abraham

2014

Contrib. Plasma Phys.

Self Cite

Particles spatially confined in trapping potentials have attracted increasing interest over the recent decade. Of particular importance are systems of charged particles, such as non-neutral plasmas, nanoplasmas, electrons in metal clusters, electrons in quantum-confined semiconductor structures ("artificial atoms"), electrons on the surface of liquid helium, ions in traps or highly charged particles (grains) in dusty plasmas. A second example of recent interest are systems with other kinds of pair interactions, including dipole interaction, which is important for excitons in quantum wells or ultracold Fermi and Bose gases in traps and optical lattices.Trapped systems are fundamentally different from macroscopic systems since they are dominated by strong spatial inhomogeneity and finite size effects (the properties depend on the exact particle number). Furthermore, by changing the strength of the confinement potential, the many-particle state of the system can be externally controlled-from weak coupling (gas-like) to strong coupling (crystal-like). While trapped classical particles are meanwhile well understood and accessible to first-principle computer simulations, their quantum counterparts still pose big challenges, both for experiment and theory. Therefore, collective properties that can be easily measured or computed and allow to diagnose the many-particle state of the system are of prime importance. It has been found that the quantum breathing mode (monopole oscillation) is one of the most important such properties. In recent years a number of theoretical studies has demonstrated that the quantum breathing mode is ideally suited to measure the coupling strength (the degree of nonideality) of a trapped system, its kinetic and interaction energy and other key observables. This give rise to a novel kind of "spectroscopy" of trapped systems.In this review these developments are summarized. The quantum breathing mode is studied for trapped fermions and bosons with Coulomb and dipole interaction, respectively. A systematic description of collective oscillations and especially the breathing mode is provided. Making use of time-dependent perturbation theory, it is shown how the corresponding breathing frequencies are connected to the properties of the initial equilibrium system. This gives rise to the application of the quantum mechanical sum rules. It is demonstrated how an improved version of the conventional sum rule formulas is suitable for an accurate description of the breathing mode in small systems. Finally, the dependence of the breathing mode on the particle number N is analyzed and the limit of large N is studied for one-dimensional and two-dimensional systems.