Top PDF Low resistivity contact to iron-pnictide superconductors

Low resistivity contact to iron pnictide superconductors

Low resistivity contact to iron-pnictide superconductors

Method of making a low resistivity electrical connection between an electrical conductor and an iron pnictide superconductor involves connecting the electrical conductor and superconductor using a tin or tin-based material therebetween, such as using a tin or tin-based solder. The superconductor can be based on doped AFe 2 As 2 , where A can be Ca, Sr, Ba, Eu or combinations thereof for purposes of illustration only.

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Ultra-low Temperature Measurements of London Penetration Depth in Iron Selenide Telluride Superconductors

Ultra-low Temperature Measurements of London Penetration Depth in Iron Selenide Telluride Superconductors

The specific heat determines the energy needed to change the temperature of a material by a specific amount. The Quantum Design Heat Capacity option measures the heat capacity at constant pressure by controlling the heat added to and removed from a sample while monitoring the resulting change in temperature. During a measurement, a known amount of heat is applied at constant power for a fixed time, and then this heating period is followed by a cooling period of the same duration. A platform heater and platform thermometer are attached to the bottom side of the sample platform. Small wires provide the electrical connection to the platform heater and platform thermometer and also provide the thermal connection and structural support for the platform. The sample is mounted to the platform by using a thin layer of Apiezon N grease, which provides the required thermal contact to the platform. The sample and platform are kept at high vacuum (0.01 mTorr) so that the thermal conductance between the sample platform and the thermal bath (puck) is totally dominated by the conductance of the wires. This gives a reproducible heat link to the bath with a corresponding time constant large enough to allow both the platform and sample to achieve sufficient thermal equilibrium during the measurement. For small size samples the amount of grease used to thermally anchor the sample is important as the heat capacity of the grease can be comparable to that of the sample under study. The amount of grease has to small enough to give negligible background but large enough to provide sufficient thermal contact. In order to probe the specific heat of the sample alone, an “addenda” was performed consisting in separately measuring the heat capacity of the grease which was later subtracted from the sample + grease HC signal. Considering that our PPMS Heat Capacity (HC) option can accommodate samples weighing at least 1 mg, an
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Tegel, Marcus Christian
  

(2011):


	Iron pnictide superconductors.


Dissertation, LMU München: Fakultät für Chemie und Pharmazie

Tegel, Marcus Christian (2011): Iron pnictide superconductors. Dissertation, LMU München: Fakultät für Chemie und Pharmazie

measurements were performed on 4.5 − 10 g of polycrystalline samples. On IN4C, the measurements were performed in the neutron energy loss mode using an inci- dent neutron wavelength of 118 pm at temperatures below 2.5 K and above 50 K (the superconducting transition). In this configuration, the elastic energy resolution of the spectrometer is about 3 meV. The detector bank covered scattering angles from 13° to 120° 2θ. For the IN6 measurements, an incident neutron wavelength of 510 pm was used. The measurements were performed in the neutron energy gain mode and the data were collected at 140 and 300 K. In this configuration the energy resolution of the spectrometer is 0.07 to 0.08 meV at elastic positions, so that a higher resolution is achieved in the low-frequency range with regard to IN4C data. The angular range of the IN4C spectrometer covers 10° – 113° 2θ. While this spec- Figure 2.1: Schematic neutron spectrum (cold neutrons) with a time-of-flight spectrometer at a specific diffraction angle. The intensity of the elastic peak was scaled down for clarity.  
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Interfaces of topological insulators and superconductors

Interfaces of topological insulators and superconductors

Some pictures of what this looks like underneath a microscope are shown in Fig. 4.6. The flake that was chosen is shown in panel d. The design is shown in panels a-c. During the first e-beam session, the blue parts, which correspond to Nb are exposed (step 3). During a second e-beam session, the orange and pink parts, which represent Au, are written (step 7). In the actual pictures in panels e and f, Nb has a silver colour and Au is, obviously, gold. During one session, the structure is written in two steps, which is why two colours per session are used. First we expose the small writefield, which is 100 µm in size and marked by the crosses. The small writefield is coloured light blue for Nb and orange for Au in the design. This is written very precisely (which takes relatively long). Then the large structures are written using a large writefield of 1000 µm, which is less precise and faster. Large writefield structure are coloured dark blue for Nb and pink for Au. The crosses are used to align the second layer (Au) with respect to the first layer (Nb). The large squares in panels c and f are the contact pads, they are 200 by 200 µm in size and we use them to glue the wires onto. Some residue of the glue is still visible in panel f (the black spots).
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Signatures of Topological Superconductors

Signatures of Topological Superconductors

Two objects will inevitably collide to each other if one tries to exchange them in a 1D system. We can overcome this problem by using two wires to form a T-junction [63] or a “crossing”-junction [17]. Here we provide an experimentally feasible way to mimic the “crossing”-junction by using the relocated edge states to form the corner junctions, as shown in Fig. 2.6(a). The corner junctions allow one to dynamically move and braid Majorana fermions by tuning side gate voltage along the relocated edge states. We can even generalize corner junctions to a checkerboard structure to fabricate a network for quantum computing in a single quantum well. One can detect these relocated edge states by the scheme shown in Fig. 2.6(b). Without the relocated edge states, the corner junction of two s-wave superconductors form a conventional Josephson junction. Single electron tunneling is forbidden in the con- ventional Josephson junction. This gives the current-phase relation as a 2π periodic function. If relocated edge states appear along the Josephson junction, one can use a gate to create Majorana fermions on the Josephson junction, as shown in Fig. 2.6(b). The Majorana fermions provide a channel to tunnel single electron across the Joseph- son junction [68], which provides a 4π periodic current-phase relation. We note that K. C. Nowack et. al.[69] recently used SQUID to map the current distribution on a HgTe quantum well. This technique may provide a practical way to measure the location of the relocated edge states.
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Improved Resistivity and Surface Morphology of Laser Treated Cr/Pd Metal Contact Sputter Deposited on Si

Improved Resistivity and Surface Morphology of Laser Treated Cr/Pd Metal Contact Sputter Deposited on Si

The as-deposited thin films commonly showing amorphous characteristics that Abstract: In this paper Cr/Pd metal contacts were deposited on Si by using DC magnetron sputtering. The metal contacts were treated using infrared Nd:YAG pulsed laser at different laser pulse energy. The metal contacts were characterized based on electrical, optical and morphology properties by using four-point probes, ultraviolet-visible spectroscopy (UV-Vis) and atomic force microscope (AFM). Measurement obtained from four point probes shown lowest resistivity values for post treatment sample after treated with 25 mJ laser pulsed energy. The measured value is 6.75 × 10 -5 Ohm-cm as compared to the as-deposited sample of 1.060
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Studies of unconventional superconductors

Studies of unconventional superconductors

Results for fits to the temperature dependence of the electronic contribution to the specific heat of FeTeo.5Seo.5 using different models for the symmetry of the superconducting gap func[r]

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Superconductors in alternating fields

Superconductors in alternating fields

values of an applied field and transport current the critical state breaks down, the fluxoids move against the viscous forces of the pinning centres and "flux flow" occurs.. the ideas be[r]

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Energy Losses in Superconductors

Energy Losses in Superconductors

Transport measurements were conducted in a Cryomech pulsed-tube closed-cycle refrigerator with the magnetic field supplied by a GMW water-cooled electromagnet. The cold tip was positioned within the magnet pole piec- es and the magnet was mounted on a rotating platform. All measurements presented here are with B parallel to the film plane directed along the bridge width. The current flows along the bridge length and so is perpendicular to B. A video/optical aligner was deviced to ensure that B//film-plane was within 25 millidegrees. Electrical re- sistivity measurements were made with a standard dc four-probe method for low currents I or with 0.005% du- ty-cycle 20 μs duration pulses for high I values. The duration of the pulses was chosen to minimize heating while maintaining a high signal-to-noise ratio. Details of the measurement techniques are given in previous re- view articles [10] [11].
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Enhancement of low-frequency fluctuations and superconductivity breakdown in Mn-doped La1-yYyFeAsO0.89F0.11 superconductors.

Enhancement of low-frequency fluctuations and superconductivity breakdown in Mn-doped La1-yYyFeAsO0.89F0.11 superconductors.

F NMR linewidth measurements show that for similar Mn contents magnetic correlations are more pronounced in the y = 0 series, at variance with what one would expect for Q = (π/a,0) spin correlations. These observations suggest that Mn doping tends to reduce fluctuations at Q = (π/a,0) and to enhance other low-frequency modes. The effect of this transfer of spectral weight on the superconducting pairing is discussed along with the charge localization induced by Mn.

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Low Dimensionality as a Factor Stimulating Formation of the Cooper Like Pairs Characteristic for Superconductors

Low Dimensionality as a Factor Stimulating Formation of the Cooper Like Pairs Characteristic for Superconductors

Critical magnetic field H c in oersteds calculated from a difference of the energy density between the paramagnetic and non-magnetic electron gas; see 45 for the singlet states curve s ;[r]

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Electrical resistivity of nickel, iron and iron-silicon alloy melts at high pressure with implications for the thermal conductivity of the Earth’s core

Electrical resistivity of nickel, iron and iron-silicon alloy melts at high pressure with implications for the thermal conductivity of the Earth’s core

Prior to emplacing the Fe-Si cylindrical sample into a high density, thick walled ceramic tube, the sample was carefully polished in such way that the diameter matched the inner diameter of the ceramic tube. Separately, the samples and the hosting ceramic tubes were also meticulously cleaned in ethyl alcohol ultrasonic bath to remove any contaminants. The ceramic tube was used to constrain the radial geometry of the molten sample, while W-discs on each end were used to contain the melt, preserve axial geometry and ensure contact with thermocouple wires/current leads during the experiments. Prior to being loaded into the 3000 ton large volume multi-anvil press, the assembled octahedra cells were heated in a vacuum furnace at about 420 K for 12 hours. The description of the octahedron cell, internal component details and setup are given in Silber et al. (2017, 2018). The average sample length was 1.5·10 -3 m. Upon compression, a 4-wire method of recording the temperature and voltage decrease separately across the sample was used, while maintaining a constant current of 0.5 A. The DC power source was a Keysight B2961A, and DC voltages were recorded using a Keysight 34470A digital multimeter, and the associated BenchVue software. A manual polarity switch was used in all experiments to account for any contribution to the voltage due to potential temperature differences between the two thermocouple junctions. Before conducting resistivity measurements, each sample was preheated at the run pressure to 1000 K and cooled slowly to ensure full contact between the W26%Re/W5%Re thermocouple wires, W-disc and a sample situated in the middle. Preheating to higher or lower temperatures did not affect the starting value of ρ. The electrical resistivity values were obtained through Ohm’s and Pouillet’s laws. The melting curve boundary was identified based on the onset of the discontinuity in the resistivity curve typically associated with melting. Multiple runs at each pressure were conducted to ensure repeatability of the phenomena and overall repeatability of data, especially for pressures 3-5 GPa, where the electrical resistivity does not exhibit any significant jump at the melt.
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AI to Superconductors

AI to Superconductors

Google DeepMind project taking neural networks to a new level A team of researchers at Google's DeepMind Technologies has been working on a means to increase the capabilities of compu[r]

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Enhancing electrical contact with a commercial polymer for electrical resistivity tomography on archaeological sites: A case study

Enhancing electrical contact with a commercial polymer for electrical resistivity tomography on archaeological sites: A case study

By applying a carbomer-based gel, the electrical contact enhanced significantly by reducing the contact resistance. This noticeable improvement was observed in the two different arrays tested: dipole-dipole (measurement #1) and pole-dipole (measurement #2), which are the common ERT arrays employed in archaeology studies. The excellent electrical contact ensures reliable performance of electrical resistivity tomography providing accurate raw data from which the subsurface structure will be inferred. Also, the physical properties of the carbomer-based gel allowed the placement of the take-out directly on the crypt floor as direct contact. Thus, eliminating the necessity of any flat base electrodes or other non-conventional electrodes. Due to the constituents of this carbomer-based gel, the harmful processes of corrosion observed on traditional electrodes, tweezers, and multicore-cable takeouts due to the added saltwater are eliminated or reduced. Moreover, this carbomer-based gel is affordable, what it is an important point related to widespread use, and since it is a commercial cosmetic product, its access is easy and unlimited. Therefore, it can be concluded that the use of this carbomer-based gel has solved the limitations of the ERT method to be applied in archaeological sites, specifically indoor studies, where is mandatory to improve the contact resistance without affecting the floor conditions.
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Electrical Resistance of Superconductors

Electrical Resistance of Superconductors

A theoretical model has been created to demonstrate and explain why some materials become superconducting at sufficiently low temperatures. (and thus exhibit zero electrical resistance), and why other materials do not. This model produces results that show how electrical resistance changes as a function of temperature. These theoretical results are consistent with experimental results whether the material is classified as a superconductor or not [8].

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Studies in the theory of multiband superconductors

Studies in the theory of multiband superconductors

There are four main classes of pnictide superconductors, and these determine the crystal structure. The classes are known as 11, 111, 122 and 1111, which indicate the number of each element in the material, and also differentiate between different crystal structures. Examples of the parent materials are 11: FeSe, FeAs, 111: LiFeAs, 122: AFe 2 As 2 (A =Ba, Sr, Ca), and 1111: RFeAsO (R =La, Nd, Sm, Gd, Er, Pr ,Nd, Ce). In these, As can also be replaced with Se. These are then doped, for example by substituting O with F, to produce a superconducting compound. Good reviews about pnictide superconductors have been written by Ishida et al. [83], Mazin and Schmalian [84], and Wilson [85].
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Low-Cost Resistivity Meter for Groundwater Exploration Using High Voltage Experimentations

Low-Cost Resistivity Meter for Groundwater Exploration Using High Voltage Experimentations

Received: 26 March, 2018 Accepted: 17 September, 2019 Abstract: Resistivity survey is very well known for the exploration of groundwater and to determine the depth of bedrock. Generally, in Pakistan local drillers rarely use resistivity meter due to high cost of commercially available equipment. Therefore, most of the wells for groundwater are drilled without any feasibility survey, which causes economic and time loss. An inexpensive resistivity meter has been developed that can help the local community to conduct a survey for groundwater. This designed equipment is handy, portable, easy to operate and can be manufactured locally. This equipment costs 500 US Dollars (USD), whereas commercially available equipment costs 2500 to 50000 USD. The designed portable device comprises of a 12V DC battery, an inverter, multiplier circuit, DPDT switch and electrodes. A 12V DC battery is fed to an inverter to achieve AC supply of 220V. The achieved AC voltage is rectified to DC-voltage which is further enhanced up-to 1300 volts using voltage multiplier circuit. This high DC voltage is called High Voltage Direct Current (HVDC). HVDC is switched at very low frequency of 1Hz. Automatic switching is being accomplished by means of DPDT relay and its control circuitry. HVDC at low frequency is applied to the earth through electrodes to determine resistivity for different materials lying inside the ground with a penetration depth of 100 meters. This portable instrument would be useful to map surface lithological layers, determine quality of groundwater and bedrock level in accurate and inexpensive way.
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Annular fast electron transport in silicon arising from low-temperature resistivity

Annular fast electron transport in silicon arising from low-temperature resistivity

beam. Subsequently, the resulting increased return current, and therefore heating in this region, drives a localized increase in resistivity for temperatures above 3 : 5 eV (up to tens of eV—see Fig. 1) and the region near the edge of the beam remains more resistive than the center [see the resis- tivity spikes in Fig. 4(d), which grow as the simulation evolves]. This, together with the pinching effect of the magnetic field arising from the first term in Eq. (1), due to the higher current density, leads to strong positive feedback which sustains the annular transport pattern as the beam propagates through the remainder of the target. Figure 4(c) shows a 2D map of the magnetic field, illustrating the strong reversal in magnetic field just inside the beam edge.
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Synthesis and characterisation of novel superconductors

Synthesis and characterisation of novel superconductors

Chapter 2 Page 48 pressure the structural integrity of the apparatus must be taken into account. A common problem with specialist glassware is the presence of pin holes in the walls of the glass as a result of joining two pieces together. This could potentially provide a point of weakness where the glass could fail if put under very low or high pressures (as well as a source of contamination). The glassware in this work was regularly checked for these problems using a spark test. This test using a high voltage gun shows any pin holes clearly allowing them to be repaired. The second test the glassware was put through was to check for defects from incomplete annealing which was done using polarised lenses. If any defects were found, detected by a change in colour of the glass when viewed using the polarised lenses, the glassware was then re-annealed. Checking key pieces of glassware in this fashion minimises the risk of failure during reaction, creating safe conditions and minimising the chance of exposing the reaction to ambient atmosphere.
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Muon studies of unconventional superconductors

Muon studies of unconventional superconductors

As discussed in Sec. 2.4, materials in which the crystal structure maintains inversion symmetry, parity is a good quantum number. In these centrosymmetric materials, electron pairing states are expected to be purely singlet or triplet, with no mixing expected. Systems lacking a centre of inversion symmetry exhibit a non-uniform lattice potential, and give rise to an antisymmetric spin-orbit coupling. The effect of this ASOC is to split the Fermi surface into separate ⃗ k-dependent bands, each of which may have their own energy gap [50]. Cooper pairs are formed of electrons that belong to different parts of this split Fermi surface - a completely different situation from the conventional case, which leads to rich and interesting new physics. Another effect of ASOC is the presence of spin fluctuations, which tend to mix spin-singlet and spin-triplet superconducting channels [51]. This mixed-parity state means that NCS superconductors might be expected to exhibit broken time-reversal symmetry, and non-trivial line nodes in the order parameter [52].
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