Whether a metallic ground state exists in a two-dimensional system beyond Anderson localization remains an unresolved question. We studied how quantum phase coherence evolves across superconductor–metal–insulator transitions through magnetoconductance quantum oscillations in nanopatterned high-temperature superconducting films. We tuned the degree of phase coherence by varying the etching time of our films. Between the superconducting and insulating regimes, we detected a robust intervening anomalous metallic state characterized by saturating resistance and oscillation amplitude at low temperatures. Our measurements suggest that the anomalous metallic state is bosonic and that the saturation of phase coherence plays a prominent role in its formation.

The development of devices suitable for heat management requires materials whose thermal properties and synthesis are well controlled.

Intercalation of metal ions into double-stranded DNA has recently been proposed as a path to efficient charge transport in DNA wires. Until now, the effect of Ag(I) intercalation between mismatched cytosine nucleobases on the conductance of DNA has not been assessed. Here we use a scanning tunneling microscopy (STM) break-junction technique to evaluate and compare the single molecule conductance of polynucleotide sequences of 11 base pairs in length. The resulting single molecule conductance for Ag(I)−polyC is found to be an order of magnitude greater than the control strand made using canonical Watson−Crick pairing. This finding suggests that Ag(I) intercalation alters the dominant electron transport process from standard π-orbital delocalization common in sequences with multiple stacked guanines to an alternate and ultimately more efficient conduit.

The temperature coeffi cient of resistance of a carbon nanotube nanocomposite with the non-conductive phase-change hydrogel Poly(N-isopropylacrylamide) is studied. This nanocomposite is found to achieve the largest reported temperature coeffi cient of resistance, ≈ − 10%/ ° C, observed in carbon nanotube-polymer nanocomposites to date. The giant temperature coefficients of resistance results from a volume-phase-transition that is induced by the humidity present in the surrounding atmosphere and that enhances the temperature dependence of the resistivity via direct changes in the tunneling resistance that electrons experience in moving between nearby carbon nanotubes. The bolometric photoresponses of this new material are also studied. The nanocomposite's enhanced responses to temperature and humidity give it great potential for sensor applications and uncooled infrared detection.

We present investigations of the superconductor to insulator transition (SIT) of uniform a-Bi films using a technique sensitive to Cooper pair phase coherence. The films are perforated with a nanohoneycomb array of holes to form a multiply connected geometry and subjected to a perpendicular magnetic field. Film magnetoresistances on the superconducting side of the SIT oscillate with a period dictated by the superconducting flux quantum and the areal hole density. The oscillations disappear close to the SIT critical point to leave a monotonically rising magnetoresistance that persists in the insulating phase. These observations indicate that the Cooper pair phase coherence length, which is infinite in the superconducting phase, collapses to a value less than the interhole spacing at this SIT. This behavior is inconsistent with the gradual reduction of the phase coherence length expected for a bosonic, phase fluctuation driven SIT. This result starkly contrasts with previous observations of oscillations persisting in the insulating phase of other films implying that there must be at least two distinct classes of disorder tuned SITs. 1 arXiv:1301.6155v2 [cond-mat.supr-con] 4 Feb 2013Superconductor to insulator quantum phase transitions (SIT) can be induced in a wide range of quasi two-dimensional superconducting systems, including elemental films, high T c superconductors, organic superconductors and superconductor graphene composites [1][2][3][4][5][6][7][8]. Remarkably, these transitions occur, nearly universally, at a critical normal state resistance, R Nc ≃ R Q = h (2e) 2 , and film resistances often show scaling behavior around this critical point. The most prominent theories that can account for these behaviors view the SIT as a Cooper pair or boson localization transition, rather than a Cooper pair breaking transition [9][10][11][12][13][14]. Recent experiments that probe films near the SIT in new ways have provided more details that support this "bosonic" picture of the SIT [15][16][17][18][19]. For example, scanning tunneling microscopy (STM) has revealed that spatial inhomogeneities develop in the order parameter on approaching the SIT suggesting that Cooper pairs localize into islands [19,20]. High frequency transport measurements indicate that a finite superfluid density persists in non-superconducting films [21]. Here, we describe experiments employing a technique that is uniquely sensitive to the length scale that diverges at a bosonic SIT: the phase coherence length ξ φ . This technique previously revealed that Cooper pairs maintain their phase coherence over 100's of nanometers through the SITs of two distinct film systems [15,22].For this work, we investigate a third film system [23][24][25] that is likely to provide the most stringent test of whether the bosonic SIT is generic to thin films. This phase sensitive technique requires patterning films with an array of nanometer-scale holes.The hole patterning creates a simply connected geometry that leads to Little-Parks-like (LP) oscillations...

Silicon microdisks with dynamically-tunable resonance spectra are achieved with nanoscale, in-plane silicon electrical contacts in a single lithographic step. Electrical current is passed through the devices to enable thermal tuning via joule heating. A 14nm wavelength shift is demonstrated with 1.6mW power consumption in devices with >20nm free spectral ranges and quality factors exceeding 20,000. Spectral shifts equal to a full width at half maximum can be achieved with approximately 10microW tuning power for a mode with quality factor of 20,000.

Subwavelength InGaAs/AlInAs microdisk lasers are demonstrated under continuous-wave optical pumping at a heat-sink temperature of 45 K. A 1.49 µm diameter, 209 nm thick microdisk lases in single-mode at a wavelength of 1.53 µm, which is identified as the whispering-gallery mode with the first radial mode number, the fifth azimuthal mode number, and a modal volume of 2.12(λ/n)(3) according to our mode simulation.

We report on uncooled mid-infrared photovoltaic responses at 300 K arising in heterojunctions of reduced graphene oxide with p-Si. Two major photoresponse spectral peaks are observed, one in the near infrared starting at 1.1 μm corresponding to electron-hole pair generation in the Si substrate, and another at wavelengths below 2.5 μm, arising from properties of the reduced graphene oxide-Si heterojunction. Our analysis of the current-voltage characteristics at various temperatures suggests that the two materials form a type-II (broken-gap) heterojunction, with a characteristic transition between direct tunneling to field emission, to over-the-barrier excitation with increasing reverse voltage. Illumination was found to affect the onset of the transition between direct tunneling and field-emission, suggesting that the mid infrared response results from the excitation of minority carriers (electrons) from the Si and their collection in the reduced graphene oxide contact. The photoresponse near 1.1 μm showed a time constant at least five times faster than the one at 2.5 μm, which points to surface defects as well as high series resistance and capacitance as potentially limiting factors in this mode of operation. With proper device engineering considerations, these devices could be promising as a graphene-based platform for infrared sensing.