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We have developed an ultrasensitive nanoscale calorimeter that enables heat capacity measurements upon minute, externally affixed (phonon-coupled) samples at low temperatures. For a 5 s measurement at 2 K, we demonstrate an unprecedented resolution of DeltaC approximately 0.5 aJ/K ( approximately 36 000 k(B)). This sensitivity is sufficient to enable heat capacity measurements upon zeptomole-scale samples or upon adsorbates with sub-monolayer coverage across the minute cross sections of these devices. We describe the fabrication and operation of these devices and demonstrate their sensitivity by measuring an adsorbed (4)He film with optimum resolution of approximately 3 x 10(-5) monolayers upon an active surface area of only approximately 1.2 x 10(-9) m(2).

Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout.

We have observed a quantized limiting value of the thermal conductance for each propagating phonon channel in a one-dimensional (1D), ballistic phonon waveguide: g_0=π^2k_B^2T/3h. To achieve this we have developed nanostructures with full three-dimensional relief that incorporate integral thermometers and heaters. These devices are comprised of an isolated thermal reservoir (phonon cavity) suspended above the sample substrate by four narrow insulating beams (phonon waveguides) with lateral dimensions ∼100 nm. We employ DC SQUID noise thermometry to measure the temperature of the phonon cavity non-perturbatively. Direct electrical contact from the suspended nanostructure to the room-temperature environment, crucial for these experiments, is attained by means of a very significant level of electrical filtering. These first experiments provide access to the mesoscopic regime for phonons, and open intriguing future possibilities for exploring thermal transport in very small systems. We are currently adapting and improving the ultrasensitive, extremely low dissipation DC SQUID techniques utilized in this work toward the ultimate goal of detecting individual thermal phonons.

The ability to transport energy is a fundamental property of the two-dimensional Dirac fermions in graphene. Electronic thermal transport in this system is relatively unexplored and is expected to show unique fundamental properties and to play an important role in future applications of graphene, including opto-electronics, plasmonics, and ultra-sensitive bolometry. Here we present measurements of bipolar, electron-diffusion and electron-phonon thermal conductances, and infer the electronic specific heat, with a minimum value of 10 $k_{\rm{B}}$ ($10^{-22}$ JK$^{-1}$) per square micron. We test the validity of the Wiedemann-Franz law and find the Lorenz number equals $1.32\times(\pi^2/3)(k_{\rm{B}}/e)^2$. The electron-phonon thermal conductance has a temperature power law $T^2$ at high doping levels, and the coupling parameter is consistent with recent theory, indicating its enhancement by impurity scattering. We demonstrate control of the thermal conductance by electrical gating and by suppressing the diffusion channel using superconducting electrodes, which sets the stage for future graphene-based single microwave photon detection.

We have constructed an integrated superfluid oscillator using various silicon processing techniques, including micromachining and electron beam lithography. This device has the advantage of a very small internal volume (0.72 mm/sup 3/). This makes it insensitive to spurious external acoustic noise which has limited the performance of larger experiments. We have tested the performance of this device in two configurations, one with a single micro-aperture and another with an additional fine tube. Both configurations demonstrate macroscopic quantum phenomena in superfluid /sup 4/He at low temperatures (0.25 K

This study focuses on domain wall resistance in Ni_(80) Fe_(20) nanowires containing narrow constrictions down to 15 nm in width. Distinct differences in the magnetoresistance curves were found to depend on the constriction size. Wider constrictions are dominated by the overall anisotropic magnetoresistance of the structure, while constrictions narrower than ∼40 nm exhibit an additional distinct contribution from a domain wall. The effect is negative and typically varies from 1% to 5%.

We have determined the features of a universal energy barrier which mediates the thermal nucleation of quantized vortices. The barrier is deduced from measurements of the intrinsic phase slip critical velocity using both dc flow and single phase slip experiments. It appears that at a given temperature a single curve can predict the outcome of all intrinsic vortex nucleation experiments for flow through small apertures.

Graphene is a material with remarkable electronic properties and exceptional thermal transport properties near room temperature, which have been well examined and understood. However at very low temperatures the thermodynamic and thermal transport properties are much less well explored and somewhat surprisingly, is expected to exhibit extreme thermal isolation. Here we demonstrate an ultra-sensitive, wide-bandwidth measurement scheme to probe the thermal transport and thermodynamic properties of the electron gas of graphene. We employ Johnson noise thermometry at microwave frequency to sensitively measure the temperature of the electron gas with resolution of $4 mK/\sqrt{Hz}$ and a bandwidth of 80 MHz. We have measured the electron-phonon coupling from 2-30 K at a charge density of $2\cdot 10^{11} cm^{-2}$. Utilizing bolometric mixing, we have sensed temperature oscillations with period of 430 ps and have determined the heat capacity of the electron gas to be $2\cdot 10^{-21} J/(K\cdot \mu m^2)$ at 5 K which is consistent with that of a two dimensional, Dirac electron gas. These measurements suggest that graphene-based devices together with wide bandwidth noise thermometry can generate substantial advances in the areas of ultra-sensitive bolometry, calorimetry, microwave and terahertz photo-detection, and bolometric mixing for applications in areas such as observational astronomy and quantum information and measurement., Comment: 8 pages, 4 figures

By fabricating a single-electron transistor onto a mechanical system in a high magnetic field, it is shown that one can manipulate both the mechanical spring constant and damping constant by adjusting a potential of a nearby gate electrode. The spring constant effect is shown to be usable to control the resonant frequency of silicon-based nanomechanical resonators, while an additional damping constant effect is relevant for the resonators built upon carbon nanotube or similar molecular-sized materials. This could prove to be a very convenient scheme to actively control the response of nanomechanical systems for a variety of applications including radio-frequency signal processing, ultrasensitive force detection, and fundamental physics explorations.

Here we describe all-electronic broadband motion detection in radio frequency nanomechanical resonators. Our technique relies upon the measurement of small motional capacitance changes using an LC impedance transformation network. We first demonstrate the technique on a single doubly clamped beam resonator with a side gate over a wide range of temperatures from 20 mK to 300 K. We then apply the technique to accomplish multiplexed readout of an array of individually addressable resonators, all embedded in a single high-frequency circuit. This technique may find use in a variety of applications ranging from ultrasensitive mass and force sensing to quantum information processing.

We have measured the dissipation and frequency of nanocrystalline-diamond nanomechanical resonators with resonant frequencies between 13.7 MHz and 157.3 MHz, over a temperature range of 1.4-274 K. Using both magnetomotive network analysis and a novel time-domain ring-down technique, we have found the dissipation in this material to have a temperature dependence roughly following T^0.2, with Q^-1 = 10^-4 at low temperatures. The frequency dependence of a large dissipation feature at ~35-55 K is consistent with thermal activation over a 0.02 eV barrier with an attempt frequency of 10 GHz., Comment: 13 pages, 3 figures, to be published in Applied Physics Letters

We have developed specially designed semiconductor devices for the measurement of thermal conductance in suspended nanostructures. By means of a novel subtractive comparison, we are able to deduce the phonon thermal conductance of individual nanoscale beams of different geometry and dopant profiles. The separate roles of important phonon scattering mechanisms are analyzed and a quantitative estimation of their respective scattering rates is obtained using the Callaway model. Diffuse surface scattering proves to be particularly important in the temperature range from 4 to 40 K. The rates of other scattering mechanisms, arising from phonon-phonon, phonon-electron, and phonon-point defect interactions, also appear to be significantly higher in nanostructures than in bulk samples.

We are performing experiments to probe directly the thermal conductance of suspended nanostructures with lateral dimensions ≈100 nm. It has been recently predicted that at low temperatures, thermal conductance in such a structure approaches a universal value of π^2k_B^2T/3h for each massless, ballistic phonon channel, independent of material characteristics. We have developed ultra-sensitive, low dissipation DC-SQUID-based noise thermometry, and extreme isolation from the electronic environment in order to perform this measurement at temperatures below 70 mK.

The critical value of the dc current of superfluid4He through a micro-aperture is found to decrease at low temperatures in the presence of3He impurities. We measure the dependence of the critical current on the pressure difference across the micro-aperture. In the temperature region where the3He affected decrease in the critical current is detected, we measure a large increase in critical current with pressure difference. The effect can be explained by the finite rate of arrival of ballistic3He atoms to a nucleation site. The critical velocity increases at high pressure difference when the rate of phase slippage becomes comparable to the flux of3He atoms.

The use of nanomechanical devices to develop a scanned probe imaging technique known as “magnetic resonance force microscopy” (MRFM) has been among the most exciting thrust areas in nanomechanics in the last decade and a half. MRFM is a visionary project with the ultimate goal of imaging and identifying individual atomic species, both on the surface and below it [1]. This would be a revolutionary tool for material science, electronic device development, and imaging biological structures. Considerable progress has been made in the development of MRFM [2] in the past decade including the detection of a single-electron spin [3].Copyright © 2005 by ASME