Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Cited by 1 publication
References 27 publications
Abstract.We report the results of NMR studies of the dynamics of 3 He adsorbed on hexagonal boron nitride. These studies can identify the phase transitions of the 2D films as a function of temperature. A thermally activated temperature dependence is observed for 2.6 < T < 8 K compared to a linear temperature dependence for 0.7 < T < 2.6 K. This linear dependence is consistent with that expected for thermal diffusion in a fluid for coverages of 0.4 -0.6 of a monolayer. IntroductionHelium-three monolayer and submonolayer films are of great interest because the different phases and microscopic dynamics that occur are dominated by quantum effects that lead to new phenomena in reduced dimensions at low temperatures [1,2]. In addition the films are ideal for testing our understanding of the quantum dynamics and spin ordering in two dimensions from first principles [3]. At low temperatures it had been postulated that the large quantum mechanical zero-point kinetic energy of the 3 He atoms could be sufficient to prevent the system from condensing as a 2D liquid in some scenarios [4], leading to a unique quantum gas at extremely low temperatures. Experimental studies by Bhattacharyya and Gasparini [5,6] offered evidence for such a phase but the majority of experiments [7][8][9] and the most recent theoretical treatments [10][11][12] do not support the existence of a low temperature gas phase. Recent thermodynamic measurements by Sato et al. [13,14], however, for 3 He adsorbed on bare graphite (and on 4 He plated graphite), have provided new evidence in support of a self-bound state for very low coverages at very low temperatures. We have carried out NMR studies at much higher coverages of 0.41 and 0.62 of a full monolayer and at higher temperatures to determine the microscopic dynamics of the 3 He atoms and the mechanisms of diffusion at coverages near the fluid-solid phase transition region [12,15]. At these coverages NMR studies by Crane and colleagues [16] for 3 He on BN showed evidence of a mixed coverage of fluid and solid components with the solid melting near 1.6K to form a dense fluid state with appreciable orientational order imposed by the substrate. We have carried out studies using a much higher NMR frequency which should help distinguish between the fluid and solid components.In addition to measuring the diffusion in the fluid phase, NMR studies can be used to determine the spin exchange rates in the solid phases. Below monolayer coverage, the 3 He monolayer forms a commensurate √ 3 × √ 3 solid structure that provides a unique testing ground for the multi-particle exchange model [17,18] invoked to explain the magnetic properties of bulk 3 He and 3 He films [15,19,20]. For example, coverages less than the ideal commensurate structure lead to a reduced probability of 3-particle exchange compared to the 2-particle exchange and
Abstract.We report the results of NMR studies of the dynamics of 3 He adsorbed on hexagonal boron nitride. These studies can identify the phase transitions of the 2D films as a function of temperature. A thermally activated temperature dependence is observed for 2.6 < T < 8 K compared to a linear temperature dependence for 0.7 < T < 2.6 K. This linear dependence is consistent with that expected for thermal diffusion in a fluid for coverages of 0.4 -0.6 of a monolayer. IntroductionHelium-three monolayer and submonolayer films are of great interest because the different phases and microscopic dynamics that occur are dominated by quantum effects that lead to new phenomena in reduced dimensions at low temperatures [1,2]. In addition the films are ideal for testing our understanding of the quantum dynamics and spin ordering in two dimensions from first principles [3]. At low temperatures it had been postulated that the large quantum mechanical zero-point kinetic energy of the 3 He atoms could be sufficient to prevent the system from condensing as a 2D liquid in some scenarios [4], leading to a unique quantum gas at extremely low temperatures. Experimental studies by Bhattacharyya and Gasparini [5,6] offered evidence for such a phase but the majority of experiments [7][8][9] and the most recent theoretical treatments [10][11][12] do not support the existence of a low temperature gas phase. Recent thermodynamic measurements by Sato et al. [13,14], however, for 3 He adsorbed on bare graphite (and on 4 He plated graphite), have provided new evidence in support of a self-bound state for very low coverages at very low temperatures. We have carried out NMR studies at much higher coverages of 0.41 and 0.62 of a full monolayer and at higher temperatures to determine the microscopic dynamics of the 3 He atoms and the mechanisms of diffusion at coverages near the fluid-solid phase transition region [12,15]. At these coverages NMR studies by Crane and colleagues [16] for 3 He on BN showed evidence of a mixed coverage of fluid and solid components with the solid melting near 1.6K to form a dense fluid state with appreciable orientational order imposed by the substrate. We have carried out studies using a much higher NMR frequency which should help distinguish between the fluid and solid components.In addition to measuring the diffusion in the fluid phase, NMR studies can be used to determine the spin exchange rates in the solid phases. Below monolayer coverage, the 3 He monolayer forms a commensurate √ 3 × √ 3 solid structure that provides a unique testing ground for the multi-particle exchange model [17,18] invoked to explain the magnetic properties of bulk 3 He and 3 He films [15,19,20]. For example, coverages less than the ideal commensurate structure lead to a reduced probability of 3-particle exchange compared to the 2-particle exchange and
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
Contact Info
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Product
Resources
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.
