Quenched Dislocation Enhanced Supersolid Ordering

Abstract

I show using Landau theory that quenched dislocations can facilitate the supersolid (SS) to normal solid (NS) transition, making it possible for the transition to occur even if it does not in a dislocationfree crystal. I make detailed predictions for the dependence of the SS to NS transition temperature Tc(L), superfluid density and dislocation spacing L, all of which can be tested against experiments. The results should also be applicable to an enormous variety of other systems, including, e.g., ferromagnets.Recent reports[1] of supersolidity -a crystal exhibiting "off-diagonal long-range order" (ODLRO) [2,3]-in solid 4 He raise many questions. First, quantum Monte Carlo simulations [4] find no supersolid phase. Second, the temperature (T ) dependence[1] of the superfluid density ρ S (T ) in the supersolid (SS) differs from that in the superfluid (SF), contradicting theory [5]. Third, no specific heat anomaly is seen at the SS to NS transition.In this paper, I propose a resolution of these puzzles. Since, depending on the material, either local compression or local dilation increase the local transition temperature T c ( r) [5], and since edge dislocations have regions of both types near their cores[6], these defects induce, in all materials, regions of elevated T c , as first noted for superconductors [7]. ODLRO therefore happens at higher temperatures on the tangled network of quenched dislocations in 4 He crystals than in the bulk, as in superconductors [7,8], and can occur even if the clean (dislocationless) lattice remains normal down to T = 0.Specifically, the DGT[5] model with quenched dislocations implies the following scenario: as temperature T decreases below what I'll call the "condensation" temperature T cond , which is always > T clean c , the transition temperature of the clean (i.e., dislocationless) lattice, each dislocation line in a tangled network of them nucleates a cylindrical supersolid "tube" tangent to it. The radius of these tubes grows with decreasing temperature.We can think of places where dislocations cross, making supersolid tubes overlap, as the "sites"of a random lattice. The sections of tube between these "sites" act as ferromagnetic "bonds". The typical length of these bonds is L, the mean dislocation spacing, which grows with annealing; L → ∞ for a clean crystal. This random lattice does not develop macroscopic supersolidity (or undergo any phase transition) at T cond , because the sites lack long-range phase coherence near T cond . However, as temperature is lowered further, such coherence inevitably develops at T = T c (L),

Local Stress and Superfluid Properties of SolidHe4

“…In this work, we explain that the origin of superfluidity in solid 4 He is large local strain in the vicinity of crystalline defects. Superfluidity along dislocations or grain boundaries can quantitatively account for the superflow through 4 He crystals observed by Ray and Hallock [18].In the past several authors have speculated about the possibility of the stress-induced supersolidity [19,20,21], especially under hydrostatic decompression since quantum effects and vacancy delocalization are expected to increase at lower densities. The phenomenology missed the attraction between vacancies which destabilizes a dilute homogeneous gas of vacancies.…”

Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? –A Review of the Past and Present Status of Research–

“…In fact, the presence of quantum effects also in high-quality 4 He solid samples points in the direction of a nonconventional state of strongly correlated-defects; a model of this kind, based on a network of dislocations was developed in ref. 124, and the transition temperature turned out to depend strongly on the defect concentration. Obviously, this argument does not exclude the possibility that some other extrinsic-defect model might agree with experiments; we simply observe that a more natural explanation comes from the other possibility as follows.…”

“…124) He found that quenched dislocations can promote the transition from a normal solid to a supersolid even if the dislocation-free crystal is normal down to T ¼ 0 K.…”

“…This case not only includes the ALC scenario 1,2) of zero-point vacancies, but also that in which the ground state contains a correlated state of vacancies 90) or vacancies and interstitials. 131) One can also consider other defects 124) or a correlated mixture of different defects. There is a consensus on the fact that the ALC scenario 1,2) of essentially independent vacancies cannot alone be the explanation of the NCRI and of other anomalies recently observed in solid 4 He.…”

Influence of elastic deformations on the supersolid transition

“…29. This article focuses on the coupling between nanoscale structure and supersolidity. 26,27 As is well appreciated, elastic strain may fundamentally affect local and mesoscopic electronic, magnetic and structural properties. There is ample evidence for significant coupling amongst the electronic degrees of freedom with the lattice distortions in cuprates, manganites, and ferroelectrics.…”