More Like this

1. Spin echo small angle neutron scattering using a continuously pumped 3He neutron polarisation analyser

   https://doi.org/10.1063/1.4909544  

   Parnell, S. R. ; Washington, A. L. ; Li, K. ; Yan, H. ; Stonaha, P. ; Li, F. ; Wang, T. ; Walsh, A. ; Chen, W. C. ; Parnell, A. J. ; et al ( February 2015 , Review of Scientific Instruments)
2. Cosmogenic 3He production rate in ilmenite and the redistribution of spallation 3He in fine-grained minerals

   https://doi.org/https://doi.org/10.1016/j.gca.2019.08.025  

   Larsen, Isaac J ; Farley, Kenneth A ; Lamb, Michael P ( January 2019 , Geochimica et cosmochimica acta)

   Cosmogenic nuclide surface exposure dating and erosion rate measurements in basaltic landscapes rely primarily on measurement of 3He in olivine or pyroxene. However, geochemical investigations using 3He have been impossible in the substantial fraction of basalts that lack separable olivine or pyroxene crystals, or where such crystals were present, but have been chemically weathered. Fine-textured basalts often contain small grains of ilmenite, a weathering-resistant mineral that is a target for cosmogenic 3He production with good He retention and straightforward mineral separation, but with a poorly constrained production rate. Here we empirically calibrate the cosmogenic 3He production rate in ilmenite by measuring 3He concentrations in basalts with fine-grained (~20 lm cross-section) ilmenite and co-existing pyroxene or olivine from the Columbia River and Snake River Plain basalt provinces in the western United States. The concentration ratio of ilmenite to pyroxene and olivine is 0.78 ± 0.02, yielding an apparent cosmogenic 3He production rate of 93.6 ± 7.7 atom g-1 yr-1 that is 20–30% greater than expected from prior theoretical and empirical estimates for compositionally similar minerals. The production rate discrepancy arises from the high energy with which cosmic ray spallation reactions emit tritium and 3He and the associated long stopping distances that cause them to redistribute within a rock. Fine-grained phases with low cosmogenic 3He production rates, like ilmenite, will have anomalously high production rates owing to net implantation of 3He from the surrounding, higher 3He production rate, matrix. Semi-quantitative modeling indicates implantation of spallation 3He increases with decreasing ilmenite grain size, leading to production rates that exceed those in a large grain by ~10% when grain radii are <150 lm. The modeling predicts that for the ilmenite grain size in our samples, implantation causes production rates to be ~20% greater than expected for a large grain, and within uncertainty resolves the discrepancy between our calibrated production rate, theory, and rates from previous work. The redistribution effect is maximized when the host rock and crystals differ substantially in mean atomic number, as they do between whole-rock basalt and ilmenite. 

   more » « less
3. Supercooling of the A phase of 3He

   https://doi.org/10.1038/s41467-022-35532-7  

   Tian, Y. ; Lotnyk, D. ; Eyal, A. ; Zhang, K. ; Zhelev, N. ; Abhilash, T. S. ; Chavez, A. ; Smith, E. N. ; Hindmarsh, M. ; Saunders, J. ; et al ( December 2023 , Nature Communications)

   Abstract Because of the extreme purity, lack of disorder, and complex order parameter, the first-order superfluid 3 He A–B transition is the leading model system for first order transitions in the early universe. Here we report on the path dependence of the supercooling of the A phase over a wide range of pressures below 29.3 bar at nearly zero magnetic field. The A phase can be cooled significantly below the thermodynamic A–B transition temperature. While the extent of supercooling is highly reproducible, it depends strongly upon the cooling trajectory: The metastability of the A phase is enhanced by transiting through regions where the A phase is more stable. We provide evidence that some of the additional supercooling is due to the elimination of B phase nucleation precursors formed upon passage through the superfluid transition. A greater understanding of the physics is essential before 3 He can be exploited to model transitions in the early universe. 

   more » « less
4. How heat propagates in liquid 3He

   https://doi.org/10.1038/s41467-024-46079-0  

   Behnia, Kamran ; Trachenko, Kostya ( February 2024 , Nature Communications)

   In Landau’s Fermi liquid picture, transport is governed by scattering between quasi-particles. The normal liquid³He conforms to this picture but only at very low temperature. Here, we show that the deviation from the standard behavior is concomitant with the fermion-fermion scattering time falling below the Planckian time,$$\frac{\hslash }{{k}_{{{{{{{{\rm{B}}}}}}}}}T}$$$\frac{\hslash }{k_{B}T}$and the thermal diffusivity of this quantum liquid is bounded by a minimum set by fundamental physical constants and observed in classical liquids. This points to collective excitations (a sound mode) as carriers of heat. We propose that this mode has a wavevector of 2k_Fand a mean free path equal to the de Broglie thermal length. This would provide an additional conducting channel with aT ^1/2temperature dependence, matching what is observed by experiments. The experimental data from 0.007 K to 3 K can be accounted for, with a margin of 10%, if thermal conductivity is the sum of two contributions: one by quasi-particles (varying as the inverse of temperature) and another by sound (following the square root of temperature).

    

   more » « less
5. Fragility of surface states in topological superfluid 3He

   https://doi.org/10.1038/s41467-021-21831-y  

   Heikkinen, P. J. ; Casey, A. ; Levitin, L. V. ; Rojas, X. ; Vorontsov, A. ; Sharma, P. ; Zhelev, N. ; Parpia, J. M. ; Saunders, J. ( December 2021 , Nature Communications)

   null (Ed.)

   Abstract Superfluid 3 He, with unconventional spin-triplet p-wave pairing, provides a model system for topological superconductors, which have attracted significant interest through potential applications in topologically protected quantum computing. In topological insulators and quantum Hall systems, the surface/edge states, arising from bulk-surface correspondence and the momentum space topology of the band structure, are robust. Here we demonstrate that in topological superfluids and superconductors the surface Andreev bound states, which depend on the momentum space topology of the emergent order parameter, are fragile with respect to the details of surface scattering. We confine superfluid 3 He within a cavity of height D comparable to the Cooper pair diameter ξ 0 . We precisely determine the superfluid transition temperature T c and the suppression of the superfluid energy gap, for different scattering conditions tuned in situ, and compare to the predictions of quasiclassical theory. We discover that surface magnetic scattering leads to unexpectedly large suppression of T c , corresponding to an increased density of low energy bound states. 

   more » « less