Effect of Magnetic Scattering on the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi>He</mml:mi></mml:math>Superfluid State in Aerogel

Sprague, D. T.; Haard, T. M.; Kycia, J. B.; Rand, M. R.; Lee, Y.; Hamot, P. J.; Halperin, W. P.

doi:10.1103/physrevlett.77.4568

Cited by 119 publications

(109 citation statements)

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“…(iv) Even though the superfluid appears to be A-like, the lack of dipole restoring torque [2] for large angle tipping pulses cannot be explained by any homogeneous p-wave structure. (v) The transition temperature ͑T c ͒ is suppressed quadratically in relatively small magnetic fields [3].In this paper, we report yet another distinct feature of 3 He in aerogel-a quantum (normal to superfluid) phase transition (QPT) at a density above the zero pressure ͑P 0͒ value. A quantum phase transition is a continuous phase transition at T 0 that reflects the alteration of the ground state of the system brought about by a change of the parameters [12,13] (in this case, the density, r) of the system.…”

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confidence: 85%

“…An aerogel concentration of ϳ2% strongly suppresses T c [1,2]. The possibility that this strong suppression can result in a T 0 phase transition and the very low temperature behavior of this system are the subject of this investigation.To put our results which we present later in perspective, we first summarize recent experimental findings: (i) The superfluid behaves as a homogeneous fluid with sharp magnetic [2,3,11] and mechanical [1,11] responses. (ii) In magnetic fields of the order of 1 kG, the superfluid phase appears to be A-like [2].…”

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confidence: 99%

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Quantum Phase Transition of3Hein Aerogel at a Nonzero Pressure

et al. 1997

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We present evidence for a nonzero pressure, T 0 superfluid phase transition of 3 He in 98.2% open aerogel. Unlike bulk 3 He which is a superfluid at T 0 at all pressures (densities) between zero and the melting pressure, 3 He in aerogel is not superfluid unless the 3 He density exceeds a critical value r c . About 90% of the 3 He added above r c contributes to the superfluid density. [S0031-9007(97) PACS numbers: 67.57. -zThe only known substance naturally free of impurities is the low temperature liquid phase of 3 He which allows the study of Fermi superfluids in their purest forms. This self-purification of 3 He has made it impossible to introduce disorder or impurities into the system. Experiments show that 3 He superfluids in aerogel display behavior [1][2][3] very different from earlier studies in confined geometries where diffuse surface scattering that suppresses T c dominates [4] and the size distribution smears out the sharp magnetic and mechanical responses of the bulk [5,6,7]. It was generally believed that p-wave superfluids are easily damaged by disorder [8], but the newest experiments [1][2][3] show that notwithstanding the T c suppression, superfluid coherence remains robust in aerogel. However, the phase diagram is completely modified despite the small volume fraction occupied by the aerogel.Aerogel is a tenuous random solid network of SiO 2 particles ͑ഠ25 Å radii͒ with fractal correlations between 30 and 1000 Å [9]. Aerogels have very large surface areas and very low densities (22.9 m 2 ͞cm 3 and 39.4 g͞l, respectively, for our samples), and very dilute aerogels occupy less than a few percent of the volume. Despite the tenuous fractal structure, the mean distance from a point in the open volume to a silica strand can be 100 Å. Since the silica diameter is smaller than the superfluid coherence length ͑j 0 150 800 Å͒, the aerogel will not behave like a surface. Instead it acts more like a collection of impurities, thus allowing the study of impurity effects on strongly interacting Fermi liquids. This "impurity" view is supported by the fact that superfluid 3 He in aerogel is coherent and homogeneous [2]. In many ways, the depairing effect of aerogel on the p-wave superfluid is similar to that of magnetic impurities on s-wave superconductors [10]. An aerogel concentration of ϳ2% strongly suppresses T c [1,2]. The possibility that this strong suppression can result in a T 0 phase transition and the very low temperature behavior of this system are the subject of this investigation.To put our results which we present later in perspective, we first summarize recent experimental findings: (i) The superfluid behaves as a homogeneous fluid with sharp magnetic [2,3,11] and mechanical [1,11] responses. (ii) In magnetic fields of the order of 1 kG, the superfluid phase appears to be A-like [2]. Recent experiments [3] show that the superfluid behaves like the B-phase if the 3 He on the surface of the aerogel is replaced with 4 He. Experiments in Manchester [11] in much lower fields (50 G) show that the mag...

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Quantum Phase Transition of3Hein Aerogel at a Nonzero Pressure

et al. 1997

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“…The free energy difference between the phases, G AB , can be determined from their susceptibility difference and the field dependence of the AB-transition [18]. The susceptibility difference in the dirty superfluid has been measured [11,15] at 18 and 32 bar, and is approximately a factor of two weaker than for the pure superfluid. We have measured the field dependence of the dirty AB-transition at 25 and 33.4 bar, Fig.1 and 2.…”

Section: Fig 2 the Phase Diagrams Of The Superfluid Phases Ofmentioning

confidence: 99%

“…We report here that indeed the superfluid constrained in aerogel exhibits supercooling and metastability similar to that of pure superfluid 3 He in the absence of aerogel; however, contrary to our expectation, there is no evidence of nucleation from the proximity effect. In addition, we have discovered a nucleation source for the pure B-superfluid that is extremely efficient and can be switched off by applying a magnetic field.The new 'dirty' superfluids are characterized by quasiparticle scattering from a silica aerogel-matrix that reduces their transition temperature and suppresses the amplitude of the order parameter [10,11]. The aerogel structure can be varied through choice of porosity, which in this work is 98%.…”

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Nucleation and Interfacial Coupling between Pure and Dirty Superfluid Phases ofH3e

et al. 2002

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The nucleation of the first order phase transition of superfluid 3 He-B from superfluid 3 He-A is quite remarkable since it requires a seed of the order of a micron. We have studied this nucleation for 3 He confined to a very dilute silica aerogel. This dirty superfluid behaves in a manner similar to previous reports for the pure superfluid. But we have discovered a novel magnetically driven nucleation switch acting on the pure superfluid B-phase. Lastly, we find the surprising result that the proximity effect between the pure and dirty superfluids at their interface is insufficient to nucleate the B-phase in either superfluid.PACS numbers:67.57. Pq,64.60.Qb,67.57.Np The A-phase of superfluid 3 He can be extensively supercooled, far into the region at low temperatures where the B-phase is thermodynamically stable [1,2]. Leggett [3,4] pointed out that the very small difference in free energy between these phases makes homogeneous nucleation of this first order phase transition so improbable as to be unrealizable within the age of the universe. If a seed of the B-phase is to grow it must surpass a critical size of a few microns, so large as to be inaccessible by thermal fluctuations. Thus the experimental fact that the B-phase nucleates at all from the A-phase indicates the existence of some heterogeneous mechanism. Quite a number of experiments have shown that ionizing radiation [1,2], vibrations [5,6], or rough surfaces [5,7] can be, under various restrictive circumstances, active sites for this nucleation; but how the process proceeds remains a major puzzle and is actively debated [8].The discovery of a class of 3 He superfluids [9,10] constrained by silica aerogel raises new questions concerning B-phase nucleation. Does the metastability of the Aphase for these superfluids follow the same pattern as for the pure case? Is there sufficient coupling between the two superfluids across their interface for nucleating the B-phase? With an appropriate choice of experimental conditions, temperature, pressure, and magnetic field, we can arrange that the interface separates two superfluids with the same, or different, order parameter symmetry. And if they are the same, we might expect the proximity effect, well known in superconductivity, to provide a nucleation source. By this we mean that the B-phase from one side of the interface should readily nucleate the B-phase in the other. We report here that indeed the superfluid constrained in aerogel exhibits supercooling and metastability similar to that of pure superfluid 3 He in the absence of aerogel; however, contrary to our expectation, there is no evidence of nucleation from the proximity effect. In addition, we have discovered a nucleation source for the pure B-superfluid that is extremely efficient and can be switched off by applying a magnetic field.The new 'dirty' superfluids are characterized by quasiparticle scattering from a silica aerogel-matrix that reduces their transition temperature and suppresses the amplitude of the order parameter [10,11]. The aerogel...

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