Some aspects of the effect of gravity on the superfluid transition in4He

Ahlers, Guenter

doi:10.1007/bf00683607

Cited by 22 publications

(4 citation statements)

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“…One might thus expect the transition to become smeared. This is what appears to be found for the liquidgas transition in a gravitational field [4,5,6], which does, however, present a physically different situation [7]. For the FM case we find that the transition remains sharp in a well-defined sense with mean-field critical behavior, even though the magnetization M (x) is position dependent and hence "smeared" in some sense [8,9].…”

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confidence: 73%

Criticality in Inhomogeneous Magnetic Systems: Application to Quantum Ferromagnets

Belitz

Kirkpatrick²,

Saha³

2007

Phys. Rev. Lett.

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We consider a φ 4 -theory with a position-dependent distance from the critical point. One realization of this model is a classical ferromagnet subject to non-uniform mechanical stress. We find a sharp phase transition where the envelope of the local magnetization vanishes uniformly. The first-order transition in a quantum ferromagnet also remains sharp. The universal mechanism leading to a tricritical point in an itinerant quantum ferromagnet is suppressed, and in principle one can recover a quantum critical point with mean-field exponents. Observable consequences of these results are discussed.PACS numbers: 75.40.Cx; 75.40.Gb; 05.70.Jk; In standard phase transitions, such as the paramagnetferromagnet transition, or the liquid-gas transition, a homogeneous order parameter (OP; the magnetization in a magnet, or the density difference in a fluid) goes to zero as one crosses from the ordered phase into the disordered one. The OP may vanish continuously, as in the case of a magnet where the transition is second order, or discontinuously, as in the case of a fluid where the transition is first order except at the critical point. An external field may preclude a homogeneous OP. This happens for a fluid in a gravitational field, which produces a position-dependent density profile [1] and in some sense destroys the critical point (see below). Due to the weakness of gravity, this is a very small effect. This raises the question whether qualitatively similar, and maybe quantitatively larger, effects can be achieved in other systems if an external field induces an inhomogeneous OP.We consider one such example, namely, a ferromagnet subject to mechanical stress. We will first discuss a classical Heisenberg magnet, and later generalize to quantum ferromagnets (FMs). Consider a metallic FM in the shape of a circular disk that is bent in the direction perpendicular to the disk plane. This leads to a position dependent mass density [2] and hence, in a metal, to a position dependent electron density and an inhomogeneous chemical potential µ. The FM transition is described by a φ 4 -theory [3], and within a Stoner model the inhomogeneous µ leads to a spatially dependent distance from criticality. Naively, this means that the system can be tuned to criticality only at special positions within the sample, not everywhere at the same time. One might thus expect the transition to become smeared. This is what appears to be found for the liquidgas transition in a gravitational field [4,5,6], which does, however, present a physically different situation [7]. For the FM case we find that the transition remains sharp in a well-defined sense with mean-field critical behavior, even though the magnetization M (x) is position dependent and hence "smeared" in some sense [8,9]. One might expect that M (x) is essentially restricted to a surface layer of fixed width, so that the dimensionality of the system is effectively reduced by one. This is not the case; we find (for a particular model of a sample of linear dimension L) that M (x) is essentia...

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confidence: 73%

Criticality in Inhomogeneous Magnetic Systems: Application to Quantum Ferromagnets

Belitz

Kirkpatrick²,

Saha³

2007

Phys. Rev. Lett.

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“…Thus there will be a gravity-induced averaging of thermophysical measurements very near the transition in a sample of finite height. In cells at constant temperature, there will be a region near T where superfluid and normal fluid 4 He will coexist ͑Ahlers, 1968a͑Ahlers, , 1991 For example, even for a superfluid sample of only 0.5 mm in height in 1g, this coexisting region will occur over a temperature range of 6.4ϫ 10 −8 K. To the extent that local properties can be measured within a cell, of course, the above limitation does not apply. For example, in thermal conductivity measurements this effect is less restrictive because the thermal gradient stratifies the column of helium, permitting local measurements that are not rounded by the pressure gradient across the entire sample ͑Day et al, 1998͒.…”

Section: Gravity Effectsmentioning

confidence: 99%

“…Note that the horizontal scales differ by a factor of 4000. From Ahlers, 1999. adjustable parameters. Over the range shown, the match is very good.…”

Section: Microgravity Measurementsmentioning

confidence: 99%

Critical phenomena in microgravity: Past, present, and future

et al. 2007

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This review provides an overview of the progress in using the low-gravity environment of space to explore critical phenomena and test modern theoretical predictions. Gravity-induced variations in the hydrostatic pressure and the resulting density gradients adversely affect ground-based measurements near fluid critical points. Performing measurements in a low-gravity environment can significantly reduce these difficulties. A number of significant experiments have been performed in low-Earth orbit. Experiments near the lambda transition in liquid helium explored the regime of large correlation lengths and tested the theoretical predictions to a level of precision that could not be obtained on Earth. Other studies have validated theoretical predictions for the divergence in the viscosity as well as the unexpected critical speeding up of the thermal equilibrium process in pure fluids near the liquid-gas critical point. We describe the scientific content of previously flown low-gravity investigations of critical phenomena as well as those in the development stage, and associated ground-based work.

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“…A small bulk thermal conductivity cell, called a "lambda device", was attached to the bottom (hot) copper plate for the determination of T λ in bulk helium. The bottom of the lambda device was 1.25 cm below that of the confinement cell, and as a result the value of T λ had to be corrected for the hydrostatic pressure difference between the bottom of the lambda device and the middle of the MCP [9,10]. Since the lambda device was attached to the bottom plate, it could only be used before and after a data acquisition sequence because the heat applied to it necessarily flowed through the confining cell.…”

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confidence: 99%

Finite-Size Scaling and Universality of the Thermal Resistivity of LiquidHe4nearTλ

et al. 2003

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We present measurements of the thermal resistivity rho(t,P,L) near the superfluid transition of 4He at saturated vapor pressure and confined in cylindrical geometries with radii L=0.5 and 1.0 microm [t identical with T/T(lambda)(P)-1]. For L=1.0 microm measurements at six pressures P are presented. At and above T(lambda) the data are consistent with a universal scaling function F(X)=(L/xi(0))(x/nu)(rho/rho(0)), X=(L/xi(0))(1/nu)t valid for all P (rho(0) and x are the pressure-dependent amplitude and effective exponent of the bulk resistivity rho, and xi=xi(0)t(-nu) is the correlation length). Indications of breakdown of scaling and universality are observed below T(lambda).

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Some aspects of the effect of gravity on the superfluid transition in4He

Cited by 22 publications

References 45 publications

Criticality in Inhomogeneous Magnetic Systems: Application to Quantum Ferromagnets

Criticality in Inhomogeneous Magnetic Systems: Application to Quantum Ferromagnets

Critical phenomena in microgravity: Past, present, and future

Finite-Size Scaling and Universality of the Thermal Resistivity of LiquidHe4nearTλ

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