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1.
No Heading Recent torsional oscillator measurements of solid 4He in Vycor glass suggest the existence of a supersolid state of matter below 175mK. We have obtained preliminary data of the specific heat of solid helium down to 80mK. No sharp feature at the onset temperature is observable to within 1%. We are currently working towards extending our measurement to lower temperatures.PACS numbers: 67.40.–w, 67.80.–s, 67.80.Mg. 相似文献
2.
The excitement following the initial report of supersolid behavior for 4He embedded in porous Vycor glass has been tempered by the realization that many of the early supersolid observations were contaminated by effects arising from an anomaly in the elastic properties of solid 4He. In an attempt to separate dynamic elastic effects from a true supersolid signal, we employed a torsional oscillator with two eigen-frequencies to study the 4He-Vycor system. We found that frequency-dependent elastic signals can entirely account for the observed period shift signals. Although, we conclude that supersolid does not exist for the 4He-Vycor case, the question of its presence in bulk samples remains open. In our current experiments we apply the two-frequency test to bulk samples of solid 4He. Again we find a frequency-dependent contribution arising from elastic effects; however, in some cases we also find a small frequency-independent contribution, which may indicate the existence of a remnant supersolid phase. Given the history of this subject such results must be treated with caution. 相似文献
3.
Torsional oscillator experiments on solid 4He have been interpreted as showing mass decoupling similar to what one observes in a superfluid. Within the context of a two-component model for the supersolid one would expect the appearance of a second, slow acoustic mode. We have searched for this mode using an acoustic resonance technique. We have used porous membranes in bulk solid 4He analogous to a second sound experiment in the superfluid. We also investigated solid helium in Vycor using piezoelectrically driven titanium diaphragms (analogous to a fourth sound experiment in the liquid). Our measurements have shown no indication of an additional sound mode in the kHz range. 相似文献
4.
Motoshi Kondo Shunichi Takada Yoshiyuki Shibayama Keiya Shirahama 《Journal of Low Temperature Physics》2007,148(5-6):695-699
In recent torsional oscillator experiments by Kim and Chan (KC), a decrease of rotational inertia has been observed in solid 4He in porous materials (Kim, E., Chan, M.H.W. in Nature 427:225, 2004; J. Low Temp. Phys. 138:859, 2005) and in a bulk annular channel (Kim, E., Chan, M.H.W. in Science 305:1941, 2004). This observation strongly suggests the existence of “non-classical rotational inertia” (NCRI), i.e. superflow, in solid 4He. In order to study such a possible “supersolid” phase, we perform torsional oscillator experiments for cylindrical solid 4He samples. We have observed decreases in rotational inertia below 200 mK for two solid samples (pressures P=4.1 and 3.0 MPa). The observed NCRI fraction at 70 mK is 0.14%, which is about 1/3 of the fraction observed in the annulus by KC. Our observation is the first experimental confirmation of the possible supersolid finding by KC. 相似文献
5.
We calculated the glassy response of solid 4He to torsional oscillations assuming a phenomenological glass model. Making only a few assumptions about the distribution of glassy relaxation times in a small subsystem of otherwise rigid solid 4He, we can account for the magnitude of the observed period shift and concomitant dissipation peak in several torsion oscillator experiments. The implications of the glass model for solid 4He are threefold: (1) The dynamics of solid 4He is governed by glassy relaxation processes. (2) The distribution of relaxation times varies significantly between different torsion oscillator experiments. (3) The mechanical response of a torsion oscillator does not require a supersolid component to account for the observed anomaly at low temperatures, though we cannot rule out its existence. 相似文献
6.
7.
Recently, Kim and Chan (Science 305:1941, 2004; Phys. Rev. Lett. 97:115302, 2006) have reported an anomalous decoupling transition of solid 4He in a torsional oscillator measurement, and interpret their results as evidence for non-classical rotational inertia and
a possible supersolid phase of 4He. The detailed nature and properties of such a “supersolid” state in 4He are still far from being clear, although there are clues from experiments involving 3He impurities, different sample cell geometries, annealing effects and grain boundary flow. Defects produced during crystal
growth or deformation (e.g. dislocations) may affect supersolidity, or even produce it, and they are expected to have significant
impact on the elastic properties of the solid. The supersolid fraction could also decouple from the lattice and produce a
decrease in the transverse sound speed. We have begun the experiments in this laboratory to study such effects, measuring
the velocity and attenuation of transverse ultrasound at 10 MHz in 4He single crystals grown at constant pressure.
相似文献
8.
Hitomi Yoshimura Rama Higashino Yoshiyuki Shibayama Keiya Shirahama 《Journal of Low Temperature Physics》2012,169(3-4):218-227
The existence of “Non-Classical Rotational Inertia (NCRI)” in solid 4He below 0.2?K has been controversial and interpreted by a number of different theories. We report on torsional oscillator measurements for 4He in a nanoporous Gelsil glass, which has a network of nanopores with 3.5?nm in diameter. In addition to the usual “low-T NCRI” with an onset temperature 0.15?K, we find a larger decrease in rotational moment of inertia in a broad range of temperature from 0.2 to 1.9?K. This “high-T inertial anomaly” is accompanied with multiple dissipation peaks, but has no dependence on torsional oscillation velocity unlike the low-T NCRI. Since the high-T anomaly is observed also in confined liquid states, it originates in amorphous solid 4He layer near the pore wall. Our result shows that different types of supersolid—like phenomena, i.e. inertial anomalies, can coexist in a single 4He sample, even with genuine superfluidity of liquid 4He. 相似文献
9.
We have studied the zero temperature phase diagram of confined 4He by means of a new exact projector Quantum Monte Carlo method: the Shadow Path Integral Ground State (SPIGS). This method is able to compute exact ground state expectation values without extrapolations and with a Shadow Wave Function (SWF) as trial variational state for the importance sampling. Thanks to the ability of SWF in describing the solid phase via spontaneously broken translational symmetry, this is an important extension which opens the possibility to study disorder phenomena in the solid phase by an exact method at zero temperature. We have applied this technique to study 4He confined in a lattice of big static objects with a purely repulsive interaction with 4He atoms. We have studied the equation of state of this system finding that a well defined liquid-solid transition is still present but with an increased freezing pressure. In the case we have studied this pressure goes from 25.2 atm for pure bulk system to about 38 atm. This is similar to what is experimentally found in 4He confined in porous material like vycor. We have found also that the disorder due to the mismatch between the crystal structure and the spherical geometry of the object induces delocalization of 4He atoms. PACS numbers: 05.10.Ln, 67.80.-s. 相似文献
10.
We present results of the search for supersolid 4He using low-frequency, low-level mechanical excitation of a solid sample grown and cooled at fixed volume. We have observed
low frequency non-linear resonances that constitute anomalous features. These features, which appear below ∼0.8 K, are absent
in 3He. The frequency, the amplitude at which the nonlinearity sets in, and the upper temperature limit of existence of these
resonances depend markedly on the sample history. 相似文献
11.
Akira Yamaguchi Takamichi Watanuki Ryuichi Masutomi Hidehiko Ishimoto 《Journal of Low Temperature Physics》2005,138(1-2):307-312
No Heading The nuclear susceptibility of liquid 3He in Grafoil pre-plated by 2.5 and 3.5 layers of 4He has been studied with a cw NMR method at temperatures between 0.7 and 100 mK under various liquid pressures. The 3.5 layers of 4He pre-plating suppresses a formation of the first and second solid 3He layer, eliminating most of surface magnetization at saturated vapor pressure. However, with increasing liquid pressure, a magnetization obeying a Curie Weiss law gradually grows in the same way as in the previous experiment for pure liquid 3He. This magnetization, induced by pressurization, is attributable to the formation of solid 3He layer above the pre-plated 4He.PACS numbers: 67.80.Jd, 75.70 Cn, 67.70.+n. 相似文献
12.
John D. Reppy Xiao Mi Alexander Justin Erich J. Mueller 《Journal of Low Temperature Physics》2012,168(3-4):175-193
The torsional oscillator is the chief instrument for investigating supersolidity in solid 4He. These oscillators can be sensitive to the elastic properties of the solid helium, which show anomalies over the same range of temperature in which the supersolid phenomenon appears. In this report we present a detailed study of the influence of the elastic properties of the solid on the periods of torsional oscillators for the various designs that have been commonly employed in supersolid measurements. We show how to design an oscillator which measures supersolidity, and how to design one which predominantly measures elasticity. We describe the use of multiple frequency TOs for the separation of the elastic and supersolid phenomena. 相似文献
13.
E. Y. Rudavskii V. N. Grigor’ev A. A. Lisunov V. A. Maidanov V. Y. Rubanskii S. P. Rubets A. S. Rybalko V. A. Tikhii 《Journal of Low Temperature Physics》2010,158(3-4):578-583
A new series of experiments has been performed to find out the conditions for the formation of a glass phase in solid 4He in the region where an anomalous behavior attributed to the supersolid effect was observed previously. A special two-chamber cell was used to deform the sample in situ. The contribution of the glass phase was identified by analyzing the measured temperature dependence of the sample pressure under different experimental conditions. It is found that the contribution of the glass phase increased sharply after deformation of the sample and practically disappears after its annealing. 相似文献
14.
M. Neumann J. Nyéki B. P. Cowan J. Saunders 《Journal of Low Temperature Physics》2005,138(1-2):391-396
No Heading We report heat capacity and magnetization measurements of 3He adsorbed on graphite pre-plated by a solid bilayer of 4He. The first 3He layer adsorbed on this composite substrate remains fluid up to and beyond layer promotion. However it is observed to solidify significantly before the second 3He layer is completed. Remarkably, at fluid coverages on the verge of solidification, we observe a distinctive heat capacity and magnetisation maximum, which occurs at progressively lower temperatures as the coverage is increased. Possible magnetic instabilities in the fluid and analogues with heavy fermion systems are discussed.PACS numbers: 67.70 n+n, 67.80. Jd 相似文献
15.
Massimo Boninsegni 《Journal of Low Temperature Physics》2011,165(3-4):67-77
Extensive Monte Carlo simulations of 4He monolayer films adsorbed on weak substrates have been carried out, aimed at ascertaining the possible occurrence of a quasi-two-dimensional supersolid phase. Only crystalline films not registered with underlying substrates are considered. Numerical results yield strong evidence that 4He will not form a supersolid film on any substrate strong enough to stabilize a crystalline layer. On weaker substrates, continuous growth of a liquid film takes place. 相似文献
16.
Alexander V. Balatsky Elihu Abrahams 《Journal of Superconductivity and Novel Magnetism》2006,19(3-5):395-399
Basing our arguments on a wavefunction that contains both positional and superfluid order, we propose a Ginzburg–Landau functional
for a supersolid with the two order parameters necessary to describe such a phase: density n
B
(r) and supersolid order parameter ψ
V
. We argue that adding lighter. 3He atoms to a 4He supersolid produces attractive regions for vacancies, leading to patches of higher T
c. On the other hand, the supersolid stiffness decreases in this granular state with increased 3He disorder. Both effects are linear in 3He concentration. 相似文献
17.
E. Dwight Adams 《Journal of Low Temperature Physics》2004,135(5-6):695-721
Research on solid 3He is reviewed beginning with the first predictions of expected behavior, which were made even before sufficient quantities were available for experimentation. The main emphasis is on the magnetic properties and physical quantities such as the melting pressure that are intimately related to magnetic properties. The discussion follows the historical sequence of discovery from the earliest experiments that were limited by cooling technology. Our understanding of the magnetically ordered phases, including the ferromagnetically ordered hcp phase is presented, concluding with some current research. Only bulk 3He is discussed, which omits many topics of recent interest such as confined geometries, adsorbed films, and helium surfaces. Brief comments are made on the connection between research on solid 3He and the research interests of Olli Lounasmaa. PACS numbers: 65.40.Gn, 65.40.-b, 67.80.Gb, 67.80.Jd, 75.30.Ds, 75.30.Et, 75.30.Kz. 相似文献
18.
John Beamish 《Journal of Low Temperature Physics》2012,168(3-4):194-220
The shear modulus of solid 4He increases below 200 mK, with the same dependence on temperature, amplitude and 3He 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 3He 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 3He 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. 相似文献
19.
I. A. Todoshchenko H. Alles H. J. Junes M. S. Manninen A. Y. Parshin V. Tsepelin 《Journal of Low Temperature Physics》2008,150(3-4):258-266
Recent discovery of a nonclassical rotational inertia (NCRI) in solid 4He below 0.2 K by Kim and Chan has revived great interest in the problem of supersolidity and initiated intensive study on
the properties of solid 4He. A direct proof that the onset of NCRI corresponds to the supersolid transition would be the observation of a corresponding
drop of the entropy of solid 4He below the transition temperature. We have measured the melting pressure of ultrapure 4He in the temperature range from 0.01 to 0.45 K with several single crystals grown at different pressures and with the accuracy
of 0.5 μbar. In addition, supplementary measurements of the pressure in liquid 4He at constant volume have been performed, which allowed us to eliminate the contribution of the temperature-dependent properties
of the pressure gauge from the measured melting pressure data. With the correction to the temperature-dependent sensitivity
of the pressure gauge, the variation of the melting pressure of 4He below 320 mK obeys the pure T
4 law due to phonons with the accuracy of 0.5 μbar, and no sign of the transition is seen (Todoshchenko et al. in JETP Lett.
85:454, 2007). This sets the upper limit of ∼5⋅10−8
R for a possible excess entropy in high-quality 4He crystals below 320 mK. At higher temperatures the contribution from rotons in the superfluid 4He has been observed. The thermal expansion coefficient of the superfluid 4He has been measured in the range from 0.01 to 0.7 K with the accuracy of ∼10−7 1/K, or by two orders of magnitude better than in previous measurements. The roton contributions to the melting pressure
and to the pressure in liquid at a constant volume are consistent and yield the value of 6.8 K for the roton gap, which is
very close to the values obtained with other methods. As no contribution due to weakly interacting vacancies to the melting
pressure of 4He has been observed, the lower limit of about 5.5 K for their activation energy can be set.
相似文献
20.
Recent torsional oscillator measurements showed evidence of non-classical rotational inertia in solid helium at temperatures below 200 mK and generated a great deal of interest in a possible supersolid state. The nature and properties of such a state are still unclear, although experiments involving 3He impurities and crystal annealing may provide clues. It would be very interesting to know whether supersolids share any of the other unusual properties of superfluids: superleaks, persistent currents, second sound and quantized vortices. We have studied the response of solid helium to pressure differences, in order to look for unusual flow properties that might be associated with supersolidity. Our measurements involved both helium confined in the nanometer pores of Vycor glass and bulk solid helium, at temperatures as low as 30 mK. Near melting, solid helium flows very easily but we did not see any evidence of superflow at low temperatures. If helium does become a supersolid at low temperatures, then its response to pressure gradients must be very different from that of liquid helium. We describe these and other experiments and discuss the role that defects may play in the low temperature behavior of solid helium. 相似文献