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Crystals 2018, 8(9), 344; https://doi.org/10.3390/cryst8090344

Temperature Dependence of the Vacancy Formation Energy in Solid 4He

1
Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
2
Departament de Física, Campus Nord B4-B5, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain
*
Author to whom correspondence should be addressed.
Received: 14 August 2018 / Accepted: 23 August 2018 / Published: 28 August 2018
(This article belongs to the Special Issue Quantum Crystals)
Full-Text   |   PDF [854 KB, uploaded 28 August 2018]   |  

Abstract

We studied the thermal effects on the behavior of incommensurate solid 4He at low temperatures using the path integral Monte Carlo method. Below a certain temperature, depending on the density and the structure of the crystal, the vacancies delocalize and a finite condensate fraction appears. We calculated the vacancy formation energy as a function of the temperature and observed a behavior compatible with a two-step structure, with a gap of few K appearing at the onset temperature of off-diagonal long-range order. Estimation of the energy cost of creating two vacancies seems to indicate an effective attractive interaction among the vacancies but the large error inherent to its numerical estimation precludes a definitive statement. View Full-Text
Keywords: vacancies; solid helium; quantum Monte Carlo vacancies; solid helium; quantum Monte Carlo
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Rota, R.; Boronat, J. Temperature Dependence of the Vacancy Formation Energy in Solid 4He. Crystals 2018, 8, 344.

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