A Glassy Contribution to the Heat Capacity of hcp 4He Solids

Su, Jung-Jung; Graf, Matthias J.; Balatsky, Alexander V.

doi:10.1007/s10909-010-0163-x

Cited by 18 publications

(23 citation statements)

References 54 publications

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“…Glassy behavior has also been inferred from the thermodynamic behavior of solid helium. Heat capacity data were reanalyzed [47] in terms of a linear T dependence which was then interpreted as evidence of the two level tunneling systems (TLS) which dominate the low temperature behavior of conventional glasses. However, a linear heat capacity could come from any excitations with a constant density of states, for example one dimensional excitations like kinks on dislocations.…”

Section: Resultsmentioning

confidence: 99%

Elastic Properties of Solid 4He

Beamish

2012

J Low Temp Phys

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The shear modulus of solid 4 He increases below 200 mK, with the same dependence on temperature, amplitude and 3 He concentration as the frequency changes recently seen in torsional oscillator (TO) experiments. These have been interpreted as mass decoupling in a supersolid but the shear modulus behavior has a natural explanation in terms of dislocations. This paper summarizes early ultrasonic and elastic experiments which established the basic properties of dislocations in solid helium. It then describes the results of our experiments on the low temperature shear modulus of solid helium. The modulus changes can be explained in terms of dislocations which are mobile above 200 mK but are pinned by 3 He impurities at low temperature. The changes we observe when we anneal or stress our crystals confirm that defects are involved. They also make it clear that the shear modulus measured at the lowest temperatures is the intrinsic value-it is the high temperature modulus which is reduced by defects. By measuring the shear modulus at different frequencies, we show that the amplitude dependence depends on stress in the crystal, rather than reflecting a superfluid-like critical velocity. The shear modulus changes shift to lower temperatures as the frequency decreases, showing that they arise from a crossover in a thermally activated relaxation process rather than from a true phase transition. The activation energy for this process is about 0.7 K but a wide distribution of energies is needed to fit the broad crossover. Although the shear modulus behavior can be explained in terms of dislocations, it is clearly related to the TO behavior. However, we made measurements on hcp 3 He which show essentially the same modulus stiffening but there is no corresponding TO anomaly. This implies that the TO frequency changes are not simply due to mechanical stiffening of the oscillator-they only occur in the Bose solid. We conclude by pointing out some of the open questions involving the elastic and TO behavior of solid helium.

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Section: Resultsmentioning

confidence: 99%

Elastic Properties of Solid 4He

Beamish

2012

J Low Temp Phys

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“…These defects can be annealed away and hence drastically change the mechanical properties of the solid. We demonstrated in previous work [12,13,[16][17][18] that the freezing out of excitations can account for the anomalies in TO and in thermodynamic experiments; a relaxation time that increases with decreasing temperature is required to describe the low-temperature anomalous features.Here we consider the dynamic response of elastic properties in 4 He crystals [19][20][21][22][23][24][25]. Very recent shear modulus measurements [19][20][21] reveal qualitative similarities with the TO experiments [1,[26][27][28][29][30][31][32].…”

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confidence: 93%

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confidence: 93%

Glass Anomaly in the Shear Modulus of SolidHe4

Su¹,

Graf

Balatsky

2010

Phys. Rev. Lett.

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The shear modulus of solid H{4}e exhibits an anomalous increase at low temperatures that behaves qualitatively similar to the frequency change in torsional oscillator experiments. We propose that this stiffening of the shear modulus with decreasing temperature can be described with a glass susceptibility assuming a temperature-dependent relaxation time τ(T). Below a characteristic crossover temperature T{X}, where ωτ(T{X})∼1, a significant slowing down of dynamics leads to an increase in the shear modulus. We predict that the maximum change of the amplitude of the shear modulus and the height of the dissipation peak are independent of the applied frequency ω. Our calculations also show a qualitative difference in behavior of the shear modulus depending on the temperature dependence of τ(T).

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“…Moreover, these TO resonant frequency increases [8][9][10][11][12][13][14][15][16] are reported to be greatly diminished by blocking the TO annulus [9,17], as if due to reconnection of that inertia. Features in the specific heat capacity ascribed to a supersolid phase transition [19,20] or disorder-induced dynamic crossover [21] also occur in this same temperature range.…”

Section: Introductionmentioning

confidence: 75%

“…Finally, there are also non-superfluid models in which solid 4 He contains a population of inertially active crystal excitations [44][45][46][47][48][49] whose relaxation time τ lengthens smoothly with falling T . These excitations are proposed variously to be a dynamical network of pinned dislocations [32,33,44,[49][50][51][52], atomic-scale tunneling two-level systems [21,48,53], or the glassy response of defects distributed throughout the solid [45][46][47]. All inertially active excitation models have the property that, as τ (T ) passes through the condition ωτ = 1, a strong maximum in |df/dT | and D should occur [14,15,[45][46][47][48][49] even though there is no supersolid T c and V c .…”

Section: Introductionmentioning

confidence: 99%

Generalized Rotational Susceptibility Studies of Solid 4He

et al. 2012

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Using a novel SQUID-based torsional oscillator (TO) technique to achieve increased sensitivity and dynamic range, we studied TO's containing solid 4 He. Below ∼250 mK, the TO resonance frequency f increases and its dissipation D passes through a maximum as first reported by Kim and Chan. To achieve unbiased analysis of such 4 He rotational dynamics, we implemented a new approach based upon (ω, T ). Upon cooling, we found that equilibration times within f (T ) and D(T ) exhibit a complex synchronized ultraslow evolution toward equilibrium indicative of glassy freezing of crystal disorder conformations which strongly influence the rotational dynamics. We explored a more specific χ −1 4 He (ω, τ (T )) with τ (T ) representing a relaxation rate for inertially active microscopic excitations. In such models, the characteristic temperature T * at which df /dT and D pass simultaneously through a maximum occurs when the TO angular frequency ω and the relaxation rate are matched: ωτ (T * ) = 1. Then, by introducing the free inertial decay (FID) technique to solid 4 He TO studies, we carried out a comprehensive map of f (T , V ) and D(T , V ) where V is the maximum TO rim velocity. These data indicated that the same microscopic excitations controlling the TO motions are generated independently by thermal and mechanical stimulation of the crystal. Moreover, a measure for their relaxation times τ (T , V ) diverges smoothly everywhere without exhibiting a critical temperature or velocity, as expected in ωτ = 1 models. Finally, following the observations of Day and Beamish, we showed that the combined temperature-velocity dependence of the TO response is indistinguishable from the combined temperature-strain dependence of the 4 He shear modulus. Together, these observations imply that ultra-slow equilibration of crystal disorder conformations controls the rotational dynamics and, for any given disorder conformation, the anomalous rotational responses of solid 4 He are associated with generation of the same microscopic excitations as those produced by direct shear strain.

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A Glassy Contribution to the Heat Capacity of hcp 4He Solids

Cited by 18 publications

References 54 publications

Elastic Properties of Solid 4He

Elastic Properties of Solid 4He

Glass Anomaly in the Shear Modulus of SolidHe4

Generalized Rotational Susceptibility Studies of Solid 4He

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