Search

Objective The antimicrobial efficacy of zinc- (ZnCl 2 ) and cetylpyridinium-chloride (CPC) and their inhibition capacity on volatile sulfur compound (VSC) production by oral bacterial strains were investigated. Design Minimum inhibitory concentrations (MIC) and growth curves were determined for ZnCl 2 , CPC, and CPC with ZnCl 2 solutions against eight oral microorganisms ( Aggregatibacter actinomycetemcomitans , Fusobacterium nucleatum, Porphyromonas gingivalis , Prevotella intermedia , Treponema denticola , Tannerella forsythia , Staphylococcus aureus and Streptococcus mutans ) known to be involved in the pathophysiology of both halitosis and periodontal disease. Gas chromatography was applied to measure VSCs (H 2 S, CH 3 SH, (CH 3 ) 2 S) production levels of each strains following exposure to the solutions. Results ZnCl 2 and CPC effectively inhibited growth of all eight strains. ZnCl 2 was generally more effective than CPC in suppressing bacterial growth excluding A. actinomycetemcomitans , P. intermedia , and T. forsythia . Synergism between CPC and ZnCl 2 was shown in A. actinomycetemcomitans . The MIC for CPC was significantly lower than ZnCl 2 . VSC production was detected in five bacterial strains ( A. actinomycetemcomitans , F. nucleatum , P. gingivalis , T. denticola , and T. forsythia ). Each bacterial strain showed unique VSCs production profiles. H 2 S was produced by F. nucleatum , P. gingivalis , and T. denticola , CH 3 SH by all five strains and (CH 3 ) 2 S by A. actinomycetemcomitans , F. nucleatum , P. gingivalis , and T. denticola . Production of CH 3 SH, the most malodorous component among the three major VSCs from mouth air was evident in F. nucleatum and T. forsythia . Conclusion Both ZnCl 2 and CPC effectively inhibit bacterial growth causative of halitosis and periodontal disease, resulting in a direct decrease of bacterial VSCs production.

Samarium hexaboride (SmB$_6$), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi$_2$Se$_3$. Here we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB$_6$. The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveal linear density of states as expected for two and one Dirac cone(s), respectively. Quite remarkably, it is found that these topological states are not protected completely within the bulk hybridization gap. A phenomenological model of the tunneling process invoking interaction of the surface states with bulk excitations (spin excitons), as predicted by a recent theory, provides a consistent explanation for all of the observed features. Our spectroscopic study supports and explains the proposed picture of the incompletely protected surface states in this topological Kondo insulator SmB$_6$., Comment: 17 pages, 3 figures, Supporting Information attached, accepted in Proc. Natl. Acad. Sci. USA

SmB$_6$, a so called Kondo insulator, is recently discussed as a candidate material for a strong topological insulator. We present detailed atomically resolved topographic information on the (001) surface from more than a dozen SmB$_6$ samples. Atomically flat, {\it in situ} cleaved surfaces often exhibit B- and Sm-terminated surfaces as well as reconstructed and non-reconstructed areas {\it coexisting} on different length scales. The terminations are unambiguously identified. In addition, electronic inhomogeneities are observed which likely result from the polar nature of the (001) surface and may indicate an inhomogeneous Sm valence at the surface of SmB$_6$. In addition, atomically resolved topographies on a (110) surface are discussed.

We report an optically induced reduction of the $f\text{\ensuremath{-}}d$ hybridization in the prototypical heavy-fermion compound ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$. We use femtosecond time- and angle-resolved photoemission spectroscopy to monitor changes of spectral weight and binding energies of the Yb $4f$ and Rh $4d$ states before the lattice temperature increases after pumping. Overall, the $f\text{\ensuremath{-}}d$ hybridization decreases smoothly with increasing electronic temperature up to $\ensuremath{\sim}250\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ but changes slope at $\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. This temperature scale coincides with the onset of coherent Kondo scattering and with thermally populating the first excited crystal electrical field level. Extending previous photoemission studies, we observe a persistent $f\text{\ensuremath{-}}d$ hybridization up to at least $\ensuremath{\sim}250\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, which is far larger than the coherence temperature defined by transport but in agreement with the temperature dependence of the noninteger Yb valence. Our data underlines the distinction of probes accessing spin and charge degrees of freedom in strongly correlated systems.

Fundamental research aside, studying three-dimensional topological insulators (3D TIs) is important for realizing advanced electronics, such as dissipationless transistors and spintronic devices. In characterizing 3D TIs, one difficulty comes from the fact that both surface and bulk conduction exist, and are markedly different. When surface conduction dominates, as in SmB${}_{6}$, characterizing the bulk value is impeded. This study offers a technique to access the bulk conductivity in the surface-dominated regime. This method is expected to see wide use for in-depth transport studies of 3D TIs.

We report the discovery of a field driven transition from a single-$q$ to multi-$q$ spin density wave (SDW) in the tetragonal heavy fermion compound ${\mathrm{CeAuSb}}_{2}$. Polarized along $\mathbf{c}$, the sinusoidal SDW amplitude is $1.8(2){\ensuremath{\mu}}_{B}/\mathrm{Ce}$ for $T\ensuremath{\ll}{T}_{N}=6.25(10)\text{ }\text{ }\mathrm{K}$ with a wave vector ${\mathbf{q}}_{1}=(\ensuremath{\eta},\ensuremath{\eta},1/2)$ $[\ensuremath{\eta}=0.136(2)]$. For $\mathbf{H}\ensuremath{\parallel}\mathbf{c}$, harmonics appearing at $2{\mathbf{q}}_{1}$ evidence a striped magnetic texture below ${\ensuremath{\mu}}_{\ensuremath{\circ}}{H}_{1}=2.78(1)\text{ }\text{ }\mathrm{T}$. Above ${H}_{1}$, these are replaced by coupled harmonics at ${\mathbf{q}}_{1}+{\mathbf{q}}_{2}=(2\ensuremath{\eta},0,0)+{\mathbf{c}}^{*}$ until ${\ensuremath{\mu}}_{\ensuremath{\circ}}{H}_{2}=5.42(5)\text{ }\text{ }\mathrm{T}$, where satellites vanish and magnetization nonlinearly approaches saturation at $1.64(2){\ensuremath{\mu}}_{B}/\mathrm{Ce}$ for ${\ensuremath{\mu}}_{\ensuremath{\circ}}H\ensuremath{\approx}7\text{ }\text{ }\mathrm{T}$.

We investigated the crystal-electric field ground state of the $4f$ manifold in the strongly correlated topological insulator ${\mathrm{SmB}}_{6}$ using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ quartet state of the Sm ${f}^{5}\text{ }\text{ }J=5/2$ configuration governs the ground-state symmetry and, hence, the topological properties of ${\mathrm{SmB}}_{6}$. Our findings contradict the results of density functional calculations reported so far.

We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb_{2}. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)μ_{B}/Ce for T≪T_{N}=6.25(10) K with a wave vector q_{1}=(η,η,1/2) [η=0.136(2)]. For H∥c, harmonics appearing at 2q_{1} evidence a striped magnetic texture below μ_{∘}H_{1}=2.78(1) T. Above H_{1}, these are replaced by coupled harmonics at q_{1}+q_{2}=(2η,0,0)+c^{*} until μ_{∘}H_{2}=5.42(5) T, where satellites vanish and magnetization nonlinearly approaches saturation at 1.64(2)μ_{B}/Ce for μ_{∘}H≈7 T.

Several technical issues and challenges are identified and investigated for the planar tunneling spectroscopy of the topological Kondo insulator SmB$_6$. Contrasting behaviors of the tunnel junctions prepared in two different ways are analyzed and explained in detail. The conventional approach based on an AlO$_\text{x}$ tunnel barrier results in unsatisfactory results due to the inter-diffusion between SmB$_6$ and deposited Al. On the contrary, plasma oxidation of SmB$_6$ crystals produces high-quality tunnel barriers on both (001) and (011) surfaces. Resultant conductance spectra are highly reproducible with clear signatures for the predicted surface Dirac fermions and the bulk hybridization gap as well. The surface states are identified to reside on two or one {\it distinguishable} Dirac cone(s) on the (001) and (011) surface, respectively, in good agreement with the recent literature. However, their topological protection is found to be limited within the low energy region due to their inevitable interaction with the bulk excitations, called spin excitons, consistent with a recent theoretical prediction. Implications of our findings on other physical properties in SmB$_6$ and also other correlated topological materials are remarked., 11 pages, 11 figures, published in Phys. Rev. B

SmB$_6$ exhibits a small (15-20 meV) bandgap at low temperatures due to hybridized $d$ and $f$ electrons, a tiny (3 meV) transport activation energy $(E_{A})$ above 4 K, and surface states accessible to transport below 2 K. We study its magnetoresistance in 60-T pulsed fields between 1.5 K and 4 K. The response of the nearly $T$-independent surface states (which show no Shubnikov-de Haas oscillations) is distinct from that of the activated bulk. $E_{A}$ shrinks by 50% under fields up to 60 T. Data up to 93 T suggest that this trend continues beyond 100 T, in contrast with previous explanations. It rules out emerging theories to explain observed exotic magnetic quantum oscillations., 12 pages, 3 figures

We have carried out bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) measurements on in-situ cleaved and ex-situ polished SmB6 single crystals. Using the multiplet-structure in the Sm 3d core level spectra, we determined reliably that the valence of Sm in bulk SmB6 is close to 2.55 at ~5 K. Temperature dependent measurements revealed that the Sm valence gradually increases to 2.64 at 300 K. From a detailed line shape analysis we can clearly observe that not only the J=0 but also the J=1 state of the Sm 4f 6 configuration becomes occupied at elevated temperatures. Making use of the polarization dependence, we were able to identify and extract the Sm 4f spectral weight of the bulk material. Finally, we revealed that the oxidized or chemically damaged surface region of the ex-situ polished SmB6 single crystal is surprisingly thin, about 1 nm only., Comment: 11 pages, 8 figures

We present results of Scanning Tunneling Microscopy and Spectroscopy (STS) measurements on the "Kondo insulator" SmB$_6$. The vast majority of surface areas investigated was reconstructed but, infrequently, also patches of varying size of non-reconstructed, Sm- or B-terminated surfaces were found. On the smallest patches, clear indications for the hybridization gap and inter-multiplet transitions were observed. On non-reconstructed surface areas large enough for coherent co-tunneling we were able to observe clear-cut Fano resonances. Our locally resolved STS indicated considerable finite conductance on all surfaces independent of their structure., 5 pages, 4 figures

Topological insulators give rise to exquisite electronic properties because of their spin-momentum locked Dirac-cone-like band structure. Recently, it has been suggested that the required opposite parities between valence and conduction band along with strong spin-orbit coupling can be realized in correlated materials. Particularly, SmB6 has been proposed as candidate material for a topological Kondo insulator. Here we observe, by utilizing scanning tunnelling microscopy and spectroscopy down to 0.35 K, several states within the hybridization gap of about ±20 meV on well characterized (001) surfaces of SmB6. The spectroscopic response to impurities and magnetic fields allows to distinguish between dominating bulk and surface contributions to these states. The surface contributions develop particularly strongly below about 7 K, which can be understood in terms of a suppressed Kondo effect at the surface. Our high-resolution data provide insight into the electronic structure of SmB6, which reconciles many current discrepancies on this compound.

Strongly correlated Kondo insulator SmB6 is known for its peculiar low temperature residual conduction, which has recently been demonstrated to arise from a robust metallic surface state, as predicted by the theory of topological Kondo insulator (TKI). Photoemission, quantum oscillation and magnetic doping experiments have provided evidence for the Dirac-like dispersion and topological protection. Questions arise as whether signatures of spin-momentum locking and electron interaction could be resolved in transport measurements. Here we report metallic conduction of surface state down to mK temperatures with saturation behaviors suggestive of Kondo effect. We observe in the surface state the weak-antilocalization (WAL) effect that is in agreement with a spin-momentum locked metallic surface. At larger perpendicular magnetic fields, the surface state exhibits an unusual linear magnetoresistance similar to those found in Bi-based topological insulators and in graphene. (Correspondence to: xia.jing@uci.edu)

We present the results of a high-resolution valence-band photoemission spectroscopic study of ${\mathrm{SmB}}_{6}$ which shows evidence for a V-shaped density of states of surface origin within the bulk gap. The spectroscopy data are interpreted in terms of the existence of heavy $4f$ surface states, which may be useful in resolving the controversy concerning the disparate surface Fermi-surface velocities observed in experiments. Most importantly, we find that the temperature dependence of the valence-band spectrum indicates that a small feature appears at a binding energy of about $\ensuremath{-}9$ meV at low temperatures. We attribute this feature to a resonance caused by the spin-exciton scattering in ${\mathrm{SmB}}_{6}$ which destroys the protection of surface states due to time-reversal invariance and spin-momentum locking. The existence of a low-energy spin exciton may be responsible for the scattering, which suppresses the formation of coherent surface quasiparticles and the appearance of the saturation of the resistivity to temperatures much lower than the coherence temperature associated with the opening of the bulk gap.

A new approach to high performance current to voltage preamplifier design is presented. The design using multiple operational amplifiers (op-amps) has a parasitic capacitance compensation network and a composite amplifier topology for fast, precision, and low noise performance. The input stage consisting of a parallel linked JFET op-amps and a high-speed bipolar junction transistor (BJT) gain stage driving the output in the composite amplifier topology, cooperating with the capacitance compensation feedback network, ensures wide bandwidth stability in the presence of input capacitance above 40 nF. The design is ideal for any two-probe measurement, including high impedance transport and scanning tunneling microscopy measurements.

A new technique to improve the integral nonlinearity of the “linear-in-dB” variable gain amplifier (VGA) by adopting a piecewise linear transfer curve rather than a single curve is presented. The conventional single curve which is the first-order approximation of the exponential function yields bigger deviation errors as the gain control code advances. The integral nonlinearity (INL) of the proposed piecewise linear curve can be managed to be smaller because one of divisional curves moves to another before the deviation becomes prominent. A generic circuit schematic without chip size overhead is suggested with its future expansion in mind, and a design in a 0.35µm CMOS process under 3.3V supply is proposed and verified.

We report the observation of two pressure-induced quantum phase transitions in a YbB6 single crystal, i.e., from a topologically trivial semiconductor to an intermediate semimetal and then from the semimetal to a possible topologically nontrivial high-pressure gapped phase through in situ high-pressure transport and synchrotron x-ray diffraction measurements. Our high-pressure absorption results reveal that the mixed-valence state in pressurized YbB6 above 15 GPa plays an important role in the formation of the high-pressure state with a reopened gap. These high-pressure results may be helpful for shedding light on the intriguing relation between the topology and the 4f electrons in the rare-earth hexaborides.

We present high-resolution angle-resolved photoemission spectroscopy studies of trivalent CeB6 and divalent BaB6 rare-earth hexaborides. We find that the Fermi surface electronic structure of CeB6 consists of large oval-shape pockets around the X points of the Brillouin zone, while the states around the zone centre 'Gamma' point are strongly renormalized. Our first-principles calculations agree with data around the X points, but not at the 'Gamma' points, indicating areas of strong renormalization located around 'Gamma'. The Ce quasi-particle states participate in formation of hotspots at the Fermi surface, while the incoherent f states hybridize and lead to the emergence of dispersive features absent in non-f counterpart BaB6. These experimental and theoretical results provide a new understanding of rare-earth hexaboride materials., 21 pages, 9 figures

We present angle-resolved photoemission studies on the rare-earth-hexaboride YbB(6), which has recently been predicted to be a topological Kondo insulator. Our data do not agree with the prediction and instead show that YbB(6) exhibits a novel topological insulator state in the absence of a Kondo mechanism. We find that the Fermi level electronic structure of YbB(6) has three 2D Dirac cone like surface states enclosing the Kramers's points, while the f orbital that would be relevant for the Kondo mechanism is ∼1 eV below the Fermi level. Our first-principles calculation shows that the topological state that we observe in YbB(6) is due to an inversion between Yb d and B p bands. These experimental and theoretical results provide a new approach for realizing novel correlated topological insulator states in rare-earth materials.

In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6.

WOS: 000360601100001, The recent conjecture of a topologically protected surface state in SmB6 and the verification of robust surface conduction below 4 K have prompted a large effort to understand surface states. Conventional Hall transport measurements allowcurrent to flow on all surfaces of a topological insulator, so such measurements are influenced by contributions from multiple surfaces of varying transport character. Instead, we study magnetotransport of SmB6 using a Corbino geometry, which can directly measure the conductivity of a single, independent surface. Both (011) and (001) crystal surfaces show a strong negative magnetoresistance at all magnetic field angles measured. The (011) surface has a carrier mobility of 122 cm(2)/V.s with a carrier density of 2.5 x 10(13) cm(-2), which are significantly lower than indicated by Hall transport studies. This mobility value can explain the failure so far to observe Shubnikov-de Haas oscillations. Analysis of the angle dependence of conductivity on the (011) surface suggests a combination of a field-dependent enhancement of the carrier density and a suppression of Kondo scattering from native oxide layer magnetic moments as the likely origin of the negative magnetoresistance. Our results also reveal a hysteretic behavior whose magnitude depends on the magnetic field sweep rate and temperature. Although this feature becomes smaller when the field sweep is slower, it does not disappear or saturate during our slowest sweep-rate measurements, which is much slower than a typical magnetotransport trace. These observations cannot be explained by quantum interference corrections such as weak antilocalization but are more likely due to an extrinsic magnetic effect such as the magnetocaloric effect or glassy ordering., National Science FoundationNational Science Foundation (NSF) [ECCS-1307744, DMR-1006500, DMR-1441965, DMR-0801253, DMR-1157490]; Department of EnergyUnited States Department of Energy (DOE) [DE-SC0008110]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); China Scholarship CouncilChina Scholarship Council; National Basic Research Program of China (973 Program)National Basic Research Program of China [2012CB922002]; State of Florida; DOEUnited States Department of Energy (DOE), We wish to acknowledge Kyunghoon Lee for his assistance with wirebonding the Corbino contacts, Juniar Lucien for polishing of crystal surfaces, and Jan Jaroszynski for discussion of the magnetocaloric effect. This work was supported by National Science Foundation Grant Nos. ECCS-1307744, DMR-1006500, DMR-1441965, and DMR-0801253, Department of Energy Award No. DE-SC0008110, the Scientific and Technological Research Council of Turkey (TUBITAK), the China Scholarship Council, and the National Basic Research Program of China (973 Program, Grant No. 2012CB922002). Device fabrication was performed in part at the Lurie Nanofabrication Facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida, and by the DOE.

The Kondo insulator SmB6 has long been known to exhibit low temperature transport anomalies whose origin is of great interest. Here we uniquely access the surface electronic structure of the anomalous transport regime by combining state-of-the-art laser- and synchrotron-based angle-resolved photoemission techniques. We observe clear in-gap states (up to 4 meV), whose temperature dependence is contingent upon the Kondo gap formation. In addition, our observed in-gap Fermi surface oddness tied with the Kramers' points topology, their coexistence with the two-dimensional transport anomaly in the Kondo hybridization regime, as well as their robustness against thermal recycling, taken together, collectively provide by-far the strongest evidence for protected surface metallicity with a Fermi surface whose topology is consistent with the theoretically predicted topological surface Fermi surface (TSS). Our observations of systematic surface electronic structure provide the fundamental electronic parameters for the anomalous Kondo ground state of the correlated electron material SmB6., Nature Commun., in press (17 pages, 4 Figs), see related papers at http://arxiv.org/abs/1306.4634 and http://scholar.google.com/citations?user=G1Qpy6MAAAAJ&hl=en

A topological insulator (TI) is an unusual quantum state in which the insulating bulk is topologically distinct from vacuum, resulting in a unique metallic surface that is robust against time-reversal invariant perturbations. These surface transport properties, however, remains difficult to be isolated from the bulk in existing TI crystals (Bi2Se3, Bi2Te3 and Sb2Te3) due to impurity caused bulk conduction. We report in large crystals of topological Kondo insulator (TKI) candidate material SmB6 the thickness-independent surface Hall effects and non- local transport, which are robust against perturbations including mechanical abrasion. These results serve as proof that at low temperatures SmB6 has a robust metallic surface that surrounds a truly insulating bulk, paving the way for transport studies of the surface state in this proposed TKI material. (xia.jing@uci.edu).

Strongly correlated electron systems show many exotic properties such as unconventional superconductity, quantum criticality, and Kondo insulating behavior. In addition, the Kondo insulator SmB6 has been predicted theoretically to be a 3D topological insulator with a metallic surface state. We report here transport measurements on doped SmB6, which show that ~3% magnetic and non-magnetic dopants in SmB6 exhibit clearly contrasting behavior, evidence that the metallic surface state is only destroyed when time reversal symmetry is broken. We find as well a quantum percolation limit of impurity concentration which transform the topological insulator into a conventional band insulator by forming impurity band. Our careful thickness dependence results show that SmB6 is the first demonstatrated perfect 3D topological insulator with virtually zero residual bulk conductivity., Comment: 17 pages, 7 figures

Recent renewed interest in the mixed valent insulator SmB6 comes from topological theory predictions and surface transport measurements of possible in-gap surface states whose existence is most directly probed by angle-resolved photoemission spectroscopy (ARPES). Early photoemission leading up to a recent flurry of ARPES studies of in-gap states is reviewed. Conflicting interpretations about the nature of the Sm 4f-5d hybridization gap and observed X-point bands between the f-states and the Fermi level are critically assessed using the important tools of photon polarization and spatial dependence which also provide additional insight into the origin of the more ambiguous {\Gamma}-point in-gap states., Comment: 10 pages, 6 figures, SCES2013 proceedings; references updated

We study the transport properties of the Kondo insulator SmB$_6$ with a specialized configuration designed to distinguish bulk-dominated conduction from surface-dominated conduction. We find that as the material is cooled below 4 K, it exhibits a crossover from bulk to surface conduction with a fully insulating bulk. We take the robustness and magnitude of the surface conductivity, as is manifest in the literature of SmB$_6$, to be strong evidence for the topological insulator metallic surface states recently predicted for this material., 23 pages, 8 figures. We updated minor editorial changes and references to match the published version

In this work, we report superconductivity in the new ternary Ta1−xHfxB system. We also show clearly evidence that appropriate amounts of Hf substitution at the Ta site induce the stabilization of the orthorhombic FeB prototype structure in this system. Bulk superconductivity is confirmed by magnetization, electronic transport and specific heat measurements. The Hall signal has temperature dependence and the specific heat data at low temperature deviate from the conventional exponential temperature dependence in Ta0.7Hf0.3B. These results suggest multiband superconductivity in this compound.

The temperature dependence of weak localization and conductance fluctuations in a ballistic quantum dot stadium was studied where the experimental data of measurements could be best fitted by including both dephasing effects of electron scatterings and thermal smearing of the states around the Fermi energy, We observed a crossover change in correlation function of fluctuations from a Lorentzian-squared form to a simple Lorentzian form as temperature was changed from low-temperature (50 mK) to high-temperature (300 mK) regimes.

Superconductivity in compounds whose crystal structure lacks inversion symmetry are known to display intriguing properties that deviate from conventional BCS superconducting behavior. Here we report magnetization, resistivity, and heat capacity measurements on polycrystalline samples of ThCoC2, which has been reported to crystallize in the non-centrosymmetric CeNiC2 prototype structure, and show clear evidence of bulk superconductivity in ThCoC2 with a critical temperature of Tc = 2.65?K. From the specific heat data we find a Sommerfeld coefficient of ? = 8.38?mJ?mol?1?K?2 and a Debye temperature of ?D = 449?K. Interestingly the Hc2 superconducting phase diagram displays positive curvature, and the specific heat at low temperature deviates from conventional exponential temperature dependence, which is suggestive of possible unconventional superconducting behavior in ThCoC2, similar to that seen in the isostructural and isoelectronic non-centrosymmetric superconductor LaNiC2.

We have developed an expandable software template to automate user created experiments. The LabVIEW based template is easily modifiable to add together user created measurements, controls, and data logging with virtually any type of laboratory equipment. We use reentrant sequential selection to implement sequence script making it possible to wrap a long series of the user created experiments and execute them in sequence. Details of software structure and application examples for scanning probe microscope and automated transport experiments using custom built laboratory electronics and a cryostat are described.

A compact, fast, and low-noise current-to-voltage amplifier is built for scanning tunneling microscopy. The amplifier consists of two amplification stages. The first stage performs low-noise transimpedance amplification by using a high performance FET operational amplifier together with a high-ohm feedback resistor of 1GΩ and a parallel trimming capacitor. The ac boosting amplifier in the second stage recovers the higher frequency above the 3dB cutoff of the first stage to extend the maximum bandwidth up to 100kHz. This two-stage current-to-voltage amplifier shows a low current noise below sub-pA rms when tuned to have the bandwidth of around 1kHz. It also guarantees stable frequency response in the presence of 1000pF input capacitance.