Thin film cryogenic thermometers defined with optical lithography for thermomagnetic measurements on films.

Resistance thermometers are common secondary thermometers in cryogenic applications. Bulk RuO2 thermometers are used in dilution refrigerators because of their low magnetoresistances in addition to their temperature sensitivity. Thermoelectric and thermomagnetic measurements require multiple thermometers to measure temperature differences. Here, we present a method to fabricate thin film RuO2 thermometers directly onto an experimental substrate. This enhances thermal contact between thermometers and films whose thermoelectric or thermomagnetic properties may be measured. Commercial thermometers have higher temperature sensitivities than the thermometers presented in this study, but commercial thermometers must be carefully heat sunk to the cryostat or sample to be useful. Thin film thermometers can be patterned with ultraviolet (UV) lithography. This allows both the size of the thermometer and its distance from the sample, when also patterned with UV lithography, to be on the order of micrometers. A universal calibration curve for these thin film thermometers has not been produced. The efficacy of these thermometers has been demonstrated through measurements of the Nernst effect in Nb. In this study, the thin film thermometers were calibrated using the cryostat thermometers.

High-resolution molecular genomic autopsy reveals complex sudden unexpected death in epilepsy risk profile.

Advanced variant detection in genes underlying risk of sudden unexpected death in epilepsy (SUDEP) can uncover extensive epistatic complexity and improve diagnostic accuracy of epilepsy-related mortality. However, the sensitivity and clinical utility of diagnostic panels based solely on established cardiac arrhythmia genes in the molecular autopsy of SUDEP is unknown. We applied the established clinical diagnostic panels, followed by sequencing and a high density copy number variant (CNV) detection array of an additional 253 related ion channel subunit genes to analyze the overall genomic variation in a SUDEP of the 3-year-old proband with severe myoclonic epilepsy of infancy (SMEI). We uncovered complex combinations of single nucleotide polymorphisms and CNVs in genes expressed in both neurocardiac and respiratory control pathways, including SCN1A, KCNA1, RYR3, and HTR2C. Our findings demonstrate the importance of comprehensive high-resolution variant analysis in the assessment of personally relevant SUDEP risk. In this case, the combination of de novo single nucleotide polymorphisms (SNPs) and CNVs in the SCN1A and KCNA1 genes, respectively, is suspected to be the principal risk factor for both epilepsy and premature death. However, consideration of the overall biologically relevant variant complexity with its extensive functional epistatic interactions reveals potential personal risk more accurately.

Suppression of the Berezinskii-Kosterlitz-Thouless transition in 2D superconductors by macroscopic quantum tunneling.

The evolution with thickness of the properties of quench-deposited homogeneous amorphous bismuth (a-Bi) thin films with a 14.67 Å amorphous antimony (a-Sb) underlayer has been studied. In contrast with the results of previous investigations on similar systems the transition between the insulating and superconducting regimes is not direct, but involves an intervening metallic regime over a range of thicknesses. For these metallic films the temperature dependencies of the resistances at temperatures above the metallic regime can be described by the Halperin-Nelson form suggesting the occurrence of a Berezinskii-Kosterlitz-Thouless (BKT) transition at lower temperatures. However, this transition never occurs as curves of R(T) flatten out as temperature is reduced. We suggest that this phenomenon is evidence of a crossover between a classical regime of thermal vortex unbinding at high temperatures and a regime of macroscopic quantum tunneling at low temperatures. The latter prevents the BKT transition from occurring.

Indications of an electronic phase transition in two-dimensional superconducting YBa2Cu3O(7-x) thin films induced by electrostatic doping.

We successfully tuned an underdoped ultrathin YBa2Cu3O(7-x) film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of p∼0.15. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.

Electrostatic control of the evolution from a superconducting phase to an insulating phase in ultrathin YBa2Cu3O(7-x) films.

The electrical transport properties of ultrathin YBa2Cu3O(7-x) films have been modified using an electric double layer transistor configuration employing an ionic liquid. A clear evolution from superconductor to insulator was observed in nominally 7 unit-cell-thick films. Using a finite size scaling analysis, curves of resistance versus temperature, R(T), over the temperature range from 6 to 22 K were found to collapse onto a single scaling function, which suggests the presence of a quantum critical point. However, the scaling fails at the lowest temperatures indicating the possible presence of an additional phase between the superconducting and insulating regimes.

Magnetic-field-tuned quantum phase transition in the insulating regime of ultrathin amorphous Bi films.

A surprisingly strong variation of resistance with a perpendicular magnetic field, and a peak in the resistance versus field, R(B) has been found in insulating films of a sequence of homogeneous, quench-condensed films of amorphous Bi undergoing a thickness-tuned superconductor-insulator transition. Isotherms of magnetoresistance, rather than resistance, versus field were found to cross at a well-defined magnetic field higher than the field corresponding to the peak in R(B). For all values of B, R(T) was found to obey an Arrhenius form. At the crossover magnetic field the prefactor became equal to the quantum resistance of electron pairs h/4e², and the activation energy returned to its zero-field value. These observations suggest that the crossover is the signature of a quantum phase transition between two distinct insulating ground states, tuned by magnetic field.

Phase diagram of electrostatically doped SrTiO3.

Electric double layer transistor configurations have been employed to electrostatically dope single crystals of insulating SrTiO(3). Here we report on the results of such doping over broad ranges of temperature and carrier concentration employing an ionic liquid as the gate dielectric. The surprising results are, with increasing carrier concentration, an apparent carrier-density dependent conductor-insulator transition, a regime of the anomalous Hall effect, suggesting magnetic ordering, and finally the appearance of superconductivity. The possible appearance of magnetic order near the boundary between the insulating and superconducting regimes is reminiscent of effects associated with quantum critical behavior in some complex compounds.

Magnetic-field-induced superconducting state in Zn nanowires driven in the normal state by an electric current.

Four-terminal resistance measurements have been carried out on Zn nanowires formed using electron-beam lithography. When driven resistive by current, these wires reenter the superconducting state upon application of small magnetic fields. The data are qualitatively different from those of previous experiments on superconducting nanowires, which revealed either negative magnetoresistance near T_{c} or high-magnetic-field-enhanced critical currents.

Arrhythmia in heart and brain: KCNQ1 mutations link epilepsy and sudden unexplained death.

Sudden unexplained death is a catastrophic complication of human idiopathic epilepsy, causing up to 18% of patient deaths. A molecular mechanism and an identified therapy have remained elusive. Here, we find that epilepsy occurs in mouse lines bearing dominant human LQT1 mutations for the most common form of cardiac long QT syndrome, which causes syncopy and sudden death. KCNQ1 encodes the cardiac KvLQT1 delayed rectifier channel, which has not been previously found in the brain. We have shown that, in these mice, this channel is found in forebrain neuronal networks and brainstem nuclei, regions in which a defect in the ability of neurons to repolarize after an action potential, as would be caused by this mutation, can produce seizures and dysregulate autonomic control of the heart. That long QT syndrome mutations in KCNQ1 cause epilepsy reveals the dual arrhythmogenic potential of an ion channelopathy coexpressed in heart and brain and motivates a search for genetic diagnostic strategies to improve risk prediction and prevention of early mortality in persons with seizure disorders of unknown origin.

Observation of discrete energy levels in a quantum confined system.

Low temperature scanning tunneling microscope images and spectroscopic data have been obtained on subnanometer size Pb clusters fabricated using the technique of buffer layer assisted growth. Discrete energy levels were resolved in current-voltage characteristics as current peaks rather than current steps. Distributions of peak voltage spacings and peak current heights were consistent with Wigner-Dyson and Porter-Thomas distributions, respectively, suggesting the relevance of random matrix theory to the description of the electronic eigenstates of the clusters. The observation of peaks rather than steps in the current-voltage characteristics is attributed to a resonant tunneling process involving the discrete energy levels of the cluster, the tip, and the states at the interface between the cluster and the substrate surface.

Electrostatic tuning of the superconductor-insulator transition in two dimensions.

Superconductivity has been induced in insulating ultrathin films of amorphous bismuth using the electric field effect. The screening of the electron-electron interaction was found to increase with electron concentration in a manner correlated with the tendency towards superconductivity. This does not preclude an increase in the density of states being important in the development of superconductivity. The superconductor-insulator transition appears to belong to the universality class of the three dimensional XY model.

Ambipolar gate effect and low temperature magnetoresistance of ultrathin La0.8Ca0.2MnO3 films.

Ultrathin La(0.8)Ca(0.2)MnO(3) films have been measured in a field-effect geometry. The gate electric field produces a significant ambipolar decrease in resistance at low temperatures. This is attributed to the development of a pseudogap in the density of states and the coupling of localized charge to strain. Within a mixed phase scenario, the gate effect and magnetoresistance are interpreted in the framework of a "general susceptibility," which describes how phase boundaries move through a hierarchical pinning landscape.

Electrical transport of spin-polarized carriers in disordered ultrathin films.

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of a collective state that forms when the carriers are spin polarized at low temperatures and in high magnetic fields.

Evidence of collective charge behavior in the insulating state of ultrathin films of superconducting metals.

Nonlinear I-V characteristics have been observed in insulating quench-condensed films which are locally superconducting. We suggest an interpretation in terms of the enhancement of conduction by the depinning of a Cooper pair charge density wave, Cooper pair crystal, or Cooper pair glass that may characterize this insulating regime. We propose that this is a more likely description than the Coulomb blockade or charge-anticharge unbinding phenomena.

Exchange field induced magnetoresistance in colossal magnetoresistance manganites.

The effect of an exchange field on the electrical transport in thin films of metallic ferromagnetic manganites has been investigated. The exchange field was induced both by direct exchange coupling in a ferromagnet/antiferromagnet multilayer and by indirect exchange interaction in a ferromagnet/paramagnet metallic superlattice. The electrical resistance of the metallic manganite layers was found to be determined by the magnitude of the vector sum of the effective exchange field and the external magnetic field.

Unique case of eleven Bell's palsy episodes.

Bell's palsy (BP) is a peripheral facial nerve paralysis of unknown etiology. It is not a life-threatening condition; however, incomplete recovery may leave an individual stigmatized functionally, occupationally as well as socially. Recurrent paralyses are seldom, noted in 7-8% of all BP cases. More than two BP relapses are even less frequent. Adour et al. (1977) reported only two patients with four BP episodes from 1700 patients. Only one patient with more than four BP recurrences in the group containing 2414 BP cases were reported by Yanagihara et al. (1984). The highest reported number of BP recurrences in the accessible literature has been nine. We are presenting an unusual patient who suffered a total of eleven relapses of an idiopathic facial nerve palsy. Description of the case along with review of the relevant literature are discussed.

Reduction of sound levels with antinoise in MR imaging.

A combination of active and passive techniques was used to reduce the sound levels in magnetic resonance imagers. These techniques were integrated into an existing audio system. Measurements of sound reduction varied with the protocol being used and averaged 9.9 dB with coaxial cabling and 14.2 dB with fiberoptic conduction of the feedback signal to a controller. Patient comfort and communication were improved.

Relationship of depth of brain lesions to consciousness and outcome after closed head injury.

Magnetic resonance (MR) imaging was performed in 94 patients who sustained closed head injury of varying severity. Results of MR studies obtained after the intensive care phase of treatment disclosed that intracranial lesions were present in about 88% of the patients. Consistent with the centripetal model of progressive brain injury proposed in 1974 by Ommaya and Gennarelli, the depth of brain lesion was positively related to the degree and duration of impaired consciousness. Further analysis indicated that the relationship between depth of brain lesion and impaired consciousness could not be attributed to secondary effects of raised intracranial pressure or to the size of intracranial lesion(s).

Progressive multifocal leukoencephalopathy and magnetic resonance imaging.

Progressive multifocal leukoencephalopathy developed in a homosexual man with underlying Hodgkin's disease. Computed tomography and magnetic resonance imaging of the brain demonstrated multiple lesions, more in gray than white matter. Brain biopsy established the diagnosis of progressive multifocal leukoencephalopathy. Magnetic resonance imaging was found useful for detecting brain lesions and for localizing an accessible lesion for biopsy.