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Register a new userQuartz tuning fork as a probe of surface waves
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Authors
Igor Todoshchenko
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Quartz tuning forks are high-quality mechanical oscillators widely used in low temperature physics as viscometers, thermometers and pressure sensors. We demonstrate that a fork placed in liquid helium near the surface of solid helium is very sensitive to the oscillations of the solid-liquid interface. We developed a double-resonance read-out technique which allowed us to detect oscillations of the surface with an accuracy of 1 Angs in 10 sec. Using this technique we have investigated crystallization waves in 4He down to 10 mK. In contrast to previous studies of crystallization waves, our measurement scheme has very low dissipation, on the order of 20 pW, which allows us to carry out experiments even at sub-mK temperatures. We propose to use this scheme in the search for crystallization waves in 3He, which exist only at temperatures well below 0.5 mK.
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Commercial quartz oscillators of the tuning-fork type with a resonant frequency of ~32 kHz have been investigated in helium liquids. The oscillators are found to have at best Q values in the range 10^5-10^6, when measured in vacuum below 1.5 K. However, the variability is large and for very low temperature operation the sensor has to be preselected. We explore their properties in the regime of linear viscous hydrodynamic response in normal and superfluid 3He and 4He, by comparing measurements to the hydrodynamic model of the sensor.
With the objective of integrating single clean, as-grown carbon nanotubes into complex circuits, we have developed a technique to grow nanotubes directly on commercially available quartz tuning forks using a high temperature CVD process. Multiple straight and aligned nanotubes bridge the >100um gap between the two tips. The nanotubes are then lowered onto contact electrodes, electronically characterized in situ, and subsequently cut loose from the tuning fork using a high current. First quantum transport measurements of the resulting devices at cryogenic temperatures display Coulomb blockade characteristics.
Magnetism and superconductivity often compete for preeminence as a materials ground state, and in the right circumstances the fluctuating remains of magnetic order can induce superconducting pairing. The intertwining of the two on the microscopic level, independent of lattice excitations, is especially pronounced in heavy fermion compounds, rare earth cuprates, and iron pnictides. Here we point out that for a helical arrangement of localized spins, a variable magnetic pitch length provides a unique tuning process from ferromagnetic to antiferromagnetic ground state in the long and short wavelength limits, respectively. Such chemical or pressure adjustable helical order naturally provides the possibility for continuous tuning between ferromagnetically and antiferromagnetically mediated superconductivity. At the same time, phonon mediated superconductivity is suppressed because of the local ferromagnetic spin configuration. We employ synchrotron-based magnetic x-ray diffraction techniques to test these ideas in the recently discovered superconductor, MnP. This sensitive probe directly reveals a reduced-moment, helical spin order at high pressure proximate to the superconducting state, with a tightened pitch in comparison to that at ambient pressure where superconductivity is absent. The correlation between magnetic pitch length and superconducting transition temperature in the (Cr/Mn/Fe)(P/As) family suggests a strategy for using spiral magnets as interlocutors for spin fluctuation mediated superconductivity.
We present magnetic and tunnel transport properties of (Ga,Mn)As/(In,Ga)As/(Ga,Mn)As structure before and after adequate annealing procedure. The conjugate increase of magnetization and tunnel magnetoresistance obtained after annealing is shown to be associated to the increase of both exchange energy $Delta$$_{exch}$ and hole concentration by reduction of the Mn interstitial atom in the top magnetic electrode. Through a 6x6 band k.p model, we established general phase diagrams of tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR) textit{vs.} (Ga,Mn)As Fermi energy (E$_F$) and spin-splitting parameter (B$_G$). This allows to give a rough estimation of the exchange energy $Delta$$_{exch}$=6B$_G$$simeq$120 meV and hole concentration p$simeq1.10^{20}$cm$^{-3}$ of (Ga,Mn)As and beyond gives the general trend of TMR and TAMR textit{vs.} the selected hole band involved in the tunneling transport.
In order to establish an objective framework for studying galaxy morphology, we have developed a quantitative two-parameter description of galactic structure that maps closely on to Hubbles original tuning fork. Any galaxy can be placed in this Hubble space, where the x-coordinate measures position along the early-to-late sequence, while the y-coordinate measures in a quantitative way the degree to which the galaxy is barred. The parameters defining Hubble space are sufficiently robust to allow the formation of Hubbles tuning fork to be mapped out to high redshifts. In the present paper, we describe a preliminary investigation of the distribution of local galaxies in Hubble space, based on the CCD imaging atlas of Frei et al. (1996). We find that barred, weakly-barred, and unbarred galaxies are remarkably well-separated on this diagnostic diagram. The spiral sequence is clearly bimodal and indeed approximates a tuning fork: strongly-barred and unbarred spirals do not simply constitute the extrema of a smooth unimodal distribution of bar strength, but rather populate two parallel sequences. Strongly barred galaxies lie on a remarkably tight sequence, strongly suggesting the presence of an underlying unifying physical process. Rather surprisingly, weakly barred systems do not seem to correspond to objects bridging the parameter space between unbarred and strongly barred galaxies, but instead form an extension of the regular spiral sequence. This relation lends support to models in which the bulges of late-type spirals originate from secular processes driven by bars.
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