Now showing items 21-40 of 111

    • Design of Resistivity Instrumentation for a He3 Cryostat and its Application to the Charge Density Wave Superconductor CuxTiSe2

      Iwachow, Jason; Department of Physics (Brock University, 2014-03-13)
      Fermi patches in quasi-two dimensional charge density waves (CDW) have not described the connection to superconductivity (SC) according to theory adequately at this point in time. The connection between CDW and SC in the quasi-two dimensional material CuxTiSe2 is an interesting one which might reveal mechanisms in unconventional superconductors. A previous Brock graduate student grew crystals of CuxTiSe2. The precise doping of the samples was not known. In order to determine the doping parameter x in CuxTiSe2, a sensitive resistivity measurement system was necessary. A new resistivity measurement system was designed and implemented utilizing an Infrared Labs HDL-10 He3 cryostat. By comparing with data from the literature, doping of two samples was investigated using the new measurement system and a Quantum Design Magnetic Property Measurement System (MPMS). Methods for determining the doping revealed that the old resistivity system would not be able to determine the CDW transition temperature of highly doped samples or doping for elongated samples due to electronic noise. Doping in one sample was found to be between x=0.06 and x=0.065. Values of doping in the second sample had a discrepancy but could be explained by incorrect sample orientation.
    • Planar Topological Defects in Unconventional Superconductors

      Przedborski, Michelle; Department of Physics (Brock University, 2013-09-12)
      In this work, we consider the properties of planar topological defects in unconventional superconductors. Specifically, we calculate microscopically the interaction energy of domain walls separating degenerate ground states in a chiral p-wave fermionic superfluid. The interaction is mediated by the quasiparticles experiencing Andreev scattering at the domain walls. As a by-product, we derive a useful general expression for the free energy of an arbitrary nonuniform texture of the order parameter in terms of the quasiparticle scattering matrix. The thesis is structured as follows. We begin with a historical review of the theories of superconductivity (Sec. 1.1), which led the way to the celebrated Bardeen-Cooper- Schrieffer (BCS) theory (Sec. 1.3). Then we proceed to the treatment of superconductors with so-called "unconventional pairing" in Sec. 1.4, and in Sec. 1.5 we introduce the specific case of chiral p-wave superconductivity. After introducing in Sec. 2 the domain wall (DW) model that will be considered throughout the work, we derive the Bogoliubov-de Gennes (BdG) equations in Sec. 3.1, which determine the quasiparticle excitation spectrum for a nonuniform superconductor. In this work, we use the semiclassical (Andreev) approximation, and solve the Andreev equations (which are a particular case of the BdG equations) in Sec. 4 to determine the quasiparticle spectrum for both the single- and two-DW textures. The Andreev equations are derived in Sec. 3.2, and the formal properties of the Andreev scattering coefficients are discussed in the following subsection. In Sec. 5, we use the transfer matrix method to relate the interaction energy of the DWs to the scattering matrix of the Bogoliubov quasiparticles. This facilitates the derivation of an analytical expression for the interaction energy between the two DWs in Sec. 5.3. Finally, to illustrate the general applicability our method, we apply it in Sec. 6 to the interaction between phase solitons in a two-band s-wave superconductor.
    • Infrared Spectroscopy of Gadolinium

      Obied, Laila; Department of Physics (Brock University, 2013-04-10)
      Measurements of the optical reflectivity of the normal incident light along c-axis [0001] have been made on a Gadolinium single crystal, for temperatures between 50 K and room temperature just above the Curie temperature of Gd, which is 293 K. And covering the spectrum range between 100 -11000 cm-I . This work is the first study of Gd in the far infrared range. In fact it fills the gap below 0.2 eV which has never been measured before. Extreme attention was paid to the fact that Gadolinium is a very reactive metal with air. Thus, the sample was mechanically polished and carefully handled during the measurement. However, temperature dependent optical measurements have been made in the same frequency range for a sample of Gd2O3. For comparison, both samples of Gd and Gd2O3 were examined by X-Ray diffraction. XRD analysis showed that the sample was pure gadolinium and the oxide layer either does not exist, or is very thin. Furthermore, this fact was supported by the absence of any of Gd2O3 features in the Gd sample reflectivity. Kramers Kronig analysis was applied to extract the optical functions from the reflectance data. The optical conductivity shows a strong temperature dependence feature in the mid-infrared. This feature disappears completely at room temperature which supports a magnetic origin.
    • Optical Properties of Sb2Te3, and Dilute Magnetic Semiconductors Sb1.97 VO.03 Te3 and Sb1.94 CrO.06 Te3

      Manson, Jason; Department of Physics (Brock University, 2013-04-09)
      This thesis reports on the optical properties of the dilute magnetic semiconductors, Sb1.97 V 0.03 Te3 and Sb1.94Cr0.06Te3, along with the parent compound Sb2Te3' These materials develop a ferromagnetic state at low temperature with Curie temperatures of 22 K and 16 K respectively. All three samples were oriented such that the electric field vector of the light was perpendicular to the c-axis. The reflectance profile of these samples in the mid-infrared (500 to 3000 cm-1) shows a pronounced plasma edge which retracts with decreasing temperature. The far-infrared region of these samples exhibits a phonon at ~ 60 cm-1 which softens as temperature decreases. Kramers-Kronig analysis and a Drude-Lorentz model were employed to determine the optical constants of the bulk samples. The real part of the optical conductivity is shown to consist of intraband contributions at frequencies below the energy gap (~0.26 eV) and interband contributions at frequencies above the energy gap. The temperature dependence of the scattering rate show that a mix of phonon and impurity scattering are present, while the signature of traditional spin disorder (magnetic) scattering was difficult to confirm.
    • Generalization of the BTK Theory to the Case of Finite Quasiparticle Lifetimes

      Rohanizadegan, Yousef; Department of Physics (Brock University, 2013-01-24)
      A generalization to the BTK theory is developed based on the fact that the quasiparticle lifetime is finite as a result of the damping caused by the interactions. For this purpose, appropriate self-energy expressions and wave functions are inserted into the strong coupling version of the Bogoliubov equations and subsequently, the coherence factors are computed. By applying the suitable boundary conditions to the case of a normal-superconducting interface, the probability current densities for the Andreev reflection, the normal reflection, the transmission without branch crossing and the transmission with branch crossing are determined. Accordingly the electric current and the differential conductance curves are calculated numerically for Nb, Pb, and Pb0.9Bi0.1 alloy. The generalization of the BTK theory by including the phenomenological damping parameter is critically examined. The observed differences between our approach and the phenomenological approach are investigated by the numerical analysis.
    • Crystal Growth and Characterization of Li0.9Mo6O17

      Xiao, Peng; Department of Physics (Brock University, 2012-12-10)
      Purple bronze Li0.9Mo6O17 has attracted researchers for its low dimensionality and corresponding properties. Although it has been studied for nearly two decades, there are still some unsolved puzzles with this unique material. Single crystals of Li0.9Mo6O17 were grown using the temperature gradient flux technique in this research. The crystal growth was optimized by experimenting different conditions and good quality crystals were obtained. X-ray diffraction results have confirmed the right phase of the crystals. Resistivity measurements and magnetic susceptibility measurements were carried out, and anomalous electronic behaviors were found. All of the samples showed the metal-insulator transition near 20K, followed by behavior that differs from sample to sample: either superconducting, metallic or insulating behavior was observed below 2K. Li0.9Mo6O17 was considered as a quasi-one-dimensional crystal and also a superconducting crystal, which implies a dimensional crossover may occur at the metal-insulator transition. A two-band scenario of the Luttinger liquid model was used to fit the resistivity data and excellent results were achieved, suggesting that the Luttinger theory is a very good candidate for the explanation of the anomalous behavior of Li0.9Mo6O17. In addition, the susceptibility measurements showed Curie paramagnetism and some temperature independent paramagnetism at low temperature. The absence of any anomalous magnetic feature near 20K where the resistivity upturn takes place, suggests that a charge density wave mechanism, which has been proposed by some researchers, is not responsible for the unique properties of Li0.9Mo6O17.
    • The Effects of Annealing URu2Si2 on the Resistivity and Meissner Effect

      Pan, Yang; Department of Physics (Brock University, 2012-09-18)
      The enigmatic heavy fermion URu2Si2, which is the subject of this thesis, has attracted intensive theoretical and experimental research since 1984 when it was firstly reported by Schlabitz et al. at a conference [1]. The previous bulk property measurements clearly showed that one second order phase transition occurs at the Hidden Order temperature THO ≈ 17.5 K and another second order phase transition, the superconducting transition, occurs at Tc ≈ 1 K. Though twenty eight years have passed, the mechanisms behind these two phase transitions are still not clear to researchers. Perfect crystals do not exist. Different kinds of crystal defects can have considerable effects on the crystalline properties. Some of these defects can be eliminated, and hence the crystalline quality improved, by annealing. Previous publications showed that some bulk properties of URu2Si2 exhibited significant differences between as-grown samples and annealed samples. The present study shows that the annealing of URu2Si2 has some considerable effects on the resistivity and the DC magnetization. The effects of annealing on the resistivity are characterized by examining how the Residual Resistivity Ratio (RRR), the fitting parameters to an expression for the temperature dependence of the resistivity, the temperatures of the local maximum and local minimum of the resistivity at the Hidden Order phase transition and the Hidden Order Transition Width ∆THO change after annealing. The plots of one key fitting parameter, the onset temperature of the Hidden Order transition and ∆THO vs RRR are compared with those of Matsuda et al. [2]. Different media used to mount samples have some impact on how effectively the samples are cooled because the media have different thermal conductivity. The DC magnetization around the superconducting transition is presented for one unannealed sample under fields of 25 Oe and 50 Oe and one annealed sample under fields of 0 Oe and 25 Oe. The DC field dependent magnetization of the annealed Sample1-1 shows a typical field dependence of a Type-II superconductor. The lower critical field Hc1 is relatively high, which may be due to flux pinning by the crystal defects.
    • Application of Reptation Quantum Monte Carlo and Related Methods to LiH

      Ospadov, Egor; Department of Physics (Brock University, 2012-09-18)
      This work investigates mathematical details and computational aspects of Metropolis-Hastings reptation quantum Monte Carlo and its variants, in addition to the Bounce method and its variants. The issues that concern us include the sensitivity of these algorithms' target densities to the position of the trial electron density along the reptile, time-reversal symmetry of the propagators, and the length of the reptile. We calculate the ground-state energy and one-electron properties of LiH at its equilibrium geometry for all these algorithms. The importance sampling is performed with a single-determinant large Slater-type orbitals (STO) basis set. The computer codes were written to exploit the efficiencies engineered into modern, high-performance computing software. Using the Bounce method in the calculation of non-energy-related properties, those represented by operators that do not commute with the Hamiltonian, is a novel work. We found that the unmodified Bounce gives good ground state energy and very good one-electron properties. We attribute this to its favourable time-reversal symmetry in its target density's Green's functions. Breaking this symmetry gives poorer results. Use of a short reptile in the Bounce method does not alter the quality of the results. This suggests that in future applications one can use a shorter reptile to cut down the computational time dramatically.
    • Crystallinity, Magnetic and Electrical Properties of Bi doped LaVO3

      Sepiedeh, Pirasteh; Department of Physics (Brock University, 2012-05-17)
      We report the results of crystal structure, magnetization and resistivity measurements of Bi doped LaVO3. X-ray diffraction (XRD) shows that if doping Bi in the La site is less than ten percent, the crystal structure of La1-xBixVO3 remains unchanged and its symmetry is orthorhombic. However, for higher Bi doping (>10%) composite compounds are found where the XRD patterns are characterized by two phases: LaVO3+V2O3. Energy-dispersive analysis of the x-ray spectroscopy (EDAX) results are used to find a proper atomic percentage of all samples. The temperature dependence of the mass magnetization of pure and single phase doped samples have transition temperatures from paramagnetic to antiferromagnetic region at TN=140 K. This measurement for bi-phasic samples indicates two transition temperatures, at TN=140 K (LaVO3) and TN=170 K (V2O3). The temperature dependence of resistivity reveals semiconducting behavior for all samples. Activation energy values for pure and doped samples are extracted by fitting resistivity versus temperature data in the framework of thermal activation process.
    • Elucidation of a mechanism of cell lysis by chorhexidine : a biophysical approach

      Komljenovic, Ivana; Department of Physics (Brock University, 2012-04-03)
      Chlorhexidine is an effective antiseptic used widely in disinfecting products (hand soap), oral products (mouthwash), and is known to have potential applications in the textile industry. Chlorhexidine has been studied extensively through a biological and biochemical lens, showing evidence that it attacks the semipermeable membrane in bacterial cells. Although extremely lethal to bacterial cells, the present understanding of the exact mode of action of chlorhexidine is incomplete. A biophysical approach has been taken to investigate the potential location of chlorhexidine in the lipid bilayer. Deuterium nuclear magnetic resonance was used to characterize the molecular arrangement of mixed phospholipid/drug formulations. Powder spectra were analyzed using the de-Pake-ing technique, a method capable of extracting both the orientation distribution and the anisotropy distribution functions simultaneously. The results from samples of protonated phospholipids mixed with deuterium-labelled chlorhexidine are compared to those from samples of deuterated phospholipids and protonated chlorhexidine to determine its location in the lipid bilayer. A series of neutron scattering experiments were also conducted to study the biophysical interaction of chlorhexidine with a model phospholipid membrane of DMPC, a common saturated lipid found in bacterial cell membranes. The results found the hexamethylene linker to be located at the depth of the glycerol/phosphate region of the lipid bilayer. As drug concentration was increased in samples, a dramatic decrease in bilayer thickness was observed. Differential scanning calorimetry experiments have revealed a depression of the DMPC bilayer gel-to-lamellar phase transition temperature with an increasing drug concentration. The enthalpy of the transition remained the same for all drug concentrations, indicating a strictly drug/headgroup interaction, thus supporting the proposed location of chlorhexidine. In combination, these results lead to the hypothesis that the drug is folded approximately in half on its hexamethylene linker, with the hydrophobic linker at the depth of the glycerol/phosphate region of the lipid bilayer and the hydrophilic chlorophenyl groups located at the lipid headgroup. This arrangement seems to suggest that the drug molecule acts as a wedge to disrupt the bilayer. In vivo, this should make the cell membrane leaky, which is in agreement with a wide range of bacteriological observations.
    • Electronic, magnetic and thermal properties of Pb₂₋x AxCrO₅ (A = K or La)

      Indovski, Biljana; Department of Physics (Brock University, 2011-10-13)
      Lead chromium oxide is a photoconductive dielectric material tha t has great potential of being used as a room temperature photodetector. In this research, we made ceramic pellets of this compound as well as potassium doped compound Pb2-xKxCr05, where x=O, 0.05, 0.125. We also investigate the properties of the lanthanum doped sample whose chemical formula is Pb1.85Lao.15Cr05' The electronic, magnetic and thermal properties of these materials have been studied. Magnetization measurements of the Pb2Cr05 sample indicate a transition at about 310 K, while for the lanthanum doped sample the transition temperature is at about 295 K indicating a paramagnetic behavior. However, the potassium doped samples are showing the transition from paramagnetic state to diamagnetic state at different temperatures for different amounts of potassium atoms present in the sample. We have studied resistivity as a function of temperature in different gas environments from 300 K to 900 K. The resistivity measurement of the parent sample indicates a conducting to insulating transition at about 300 K and upon increasing the temperature further, above 450 K the sample becomes an ionic conductor. As temperature increases a decrease in resistance is observed in the lanthanum/potassium doped samples. Using Differential Scanning Calorimetry experiment an endothermic peak is observed for the Pb2Cr05 and lanthanum/potassium doped samples at about 285 K.
    • Crystal growth, characterization and point contact spectroscopy on CuxTiSe₂

      Potalivo, Michael; Department of Physics (Brock University, 2011-05-17)
      Various s e t s of single c rys t a l s and poly c rys t a l s of Cux TiSe2 were grown. X- r ay diffraction and ene rgy dispersive spe c t ros copy r e sul t s verified tha t the c rys t a l s were the cor r e c t compos i t ion and c rys t a l s t ruc tur e . Re s i s t ivi ty me a sur ement s and magne t i c sus c ept ibi l i ty me a sur ement s de t e rmined the supe r conduc t ing t r ans i t ion t empe r a tur e s for the c rys t a l s . The c rys t a l s in each growth had various supe r conduc t ing t r ans i t ion t empe r a tur e s . Also, the me a sur ement s indi c a t ed tha t the c rys t a l s were inhomogeneous. Point cont a c t spe c t ros copy expe r iment s were employed on various single c rys t a l s . Inspe c t ion of the da t a indi c a t ed tha t the ma t e r i a l ha s a single ene rgy gap . A progr am was bui l t ut i l i z ing the Levenbe rg-Ma rqua rdt me thod and theory on point cont a c t spe c t ros copy to de t e rmine the supe r conduc t ing ene rgy gap. Plot s of the supe r conduc t ing ene rgy gap a t various t empe r a tur e s were in di s agr e ement wi th wha t was expe c t ed for a convent iona l supe r conduc tor .
    • Surface effect ferromagnetism in pure and reduced strontium titanate

      DesRoches, Brandon J.; Department of Physics (Brock University, 2011-03-08)
      A room temperature ferromagnetic hysteresis is observed in single crystal strontium titanate substrates as purchased from several manufacturers. It was found that polishing all sides of the substrates removed this observed hysteresis, suggesting that the origin of the ferromagnetic behavior resides on the surface of the substrates. X-ray diffraction and energy dispersive x-ray spectra were measured however they were unable to detect any impurity phases. In similar semiconducting oxides it was previously suggested that ferromagnetism could originate in oxygen vacancies or from disorder within the single crystal. To this end substrates were annealed in both air and vacuum in a range of temperatures (600°C to 1100°G) to both create bulk oxygen vacancies and to heal surface damage. Annealing in vacuum was found to create a measureable number of oxygen vacancies however their creation could not be correlated to the ferromagnetic signal of the substrate. Annealing in air was found to effect the remnant moment of the substrate as well as the width of the x-ray diffraction peaks on the unpolished face, weakly suggesting a relation between surface based disorder and ferromagnetism. Argon ion bombardment was employed to create a layer of surface disorder in the polished crystal, however it was not found to induce ferromagnetism. It was found that acid etching was sufficient to remove the ferromagnetism from as purchased samples and similarly simulated handling with stainless steel tweezers was sufficient to re-create the ferromagnetism. It is suggested that the origin of this ferromagnetism in SrTi03 is surface contaminants (mainly iron).
    • Far infared reflectance along the C-axis of the charge stripe superconductor La1.875Ba0.125CuO4.

      Dempsie, Brad; Department of Physics (Brock University, 2011-03-08)
      Reflectance measurements along the c-axis of La1.875 Bao.125CU04 at temperatures above(6K) and below(O.5K) the bulk superconducting transition temperature(3K) were performed using a Bruker rapid scan spectrometer and a Martin-Puplett polarizing spectrometer. It was found that when polarized light reflected from a sample the Bruker rapid scan spectrometer has a low frequency cutoff of lOcm-1 while the Martin-Puplett polarizing spectrometer has a low frequency cutoff of 6cm-1 A superconducting pla ma edge was absent in all measurements taken. It was concluded that if a superconducting plasma edge exists in La1.875Bao.125CU04 it is below 6cm-1.
    • Developing a numerical inverse-theory-based extraction of orientation-dependent relaxation rates from partially- relaxed spectra

      Ghamari, Mohammad Sedigh; Department of Physics (Brock University, 2010-03-09)
      Second-rank tensor interactions, such as quadrupolar interactions between the spin- 1 deuterium nuclei and the electric field gradients created by chemical bonds, are affected by rapid random molecular motions that modulate the orientation of the molecule with respect to the external magnetic field. In biological and model membrane systems, where a distribution of dynamically averaged anisotropies (quadrupolar splittings, chemical shift anisotropies, etc.) is present and where, in addition, various parts of the sample may undergo a partial magnetic alignment, the numerical analysis of the resulting Nuclear Magnetic Resonance (NMR) spectra is a mathematically ill-posed problem. However, numerical methods (de-Pakeing, Tikhonov regularization) exist that allow for a simultaneous determination of both the anisotropy and orientational distributions. An additional complication arises when relaxation is taken into account. This work presents a method of obtaining the orientation dependence of the relaxation rates that can be used for the analysis of the molecular motions on a broad range of time scales. An arbitrary set of exponential decay rates is described by a three-term truncated Legendre polynomial expansion in the orientation dependence, as appropriate for a second-rank tensor interaction, and a linear approximation to the individual decay rates is made. Thus a severe numerical instability caused by the presence of noise in the experimental data is avoided. At the same time, enough flexibility in the inversion algorithm is retained to achieve a meaningful mapping from raw experimental data to a set of intermediate, model-free
    • X-ray diffraction of a gram-negative bacterial membrane mimetic

      Razavi, Panteha.; Department of Physics (Brock University, 2009-01-28)
      This thesis applies x-ray diffraction to measure he membrane structure of lipopolysaccharides and to develop a better model of a LPS bacterial melilbrane that can be used for biophysical research on antibiotics that attack cell membranes. \iVe ha'e Inodified the Physics department x-ray machine for use 3.'3 a thin film diffractometer, and have lesigned a new temperature and relative humidity controlled sample cell.\Ve tested the sample eel: by measuring the one-dimensional electron density profiles of bilayers of pope with 0%, 1%, 1G :VcJ, and 100% by weight lipo-polysaccharide from Pse'udo'lTwna aeTuginosa. Background VVe now know that traditional p,ntibiotics ,I,re losing their effectiveness against ever-evolving bacteria. This is because traditional antibiotic: work against specific targets within the bacterial cell, and with genetic mutations over time, themtibiotic no longer works. One possible solution are antimicrobial peptides. These are short proteins that are part of the immune systems of many animals, and some of them attack bacteria directly at the membrane of the cell, causing the bacterium to rupture and die. Since the membranes of most bacteria share common structural features, and these featuret, are unlikely to evolve very much, these peptides should effectively kill many types of bacteria wi Lhout much evolved resistance. But why do these peptides kill bacterial cel: '3 , but not the cells of the host animal? For gramnegative bacteria, the most likely reason is that t Ileir outer membrane is made of lipopolysaccharides (LPS), which is very different from an animal :;ell membrane. Up to now, what we knovv about how these peptides work was likely done with r !10spholipid models of animal cell membranes, and not with the more complex lipopolysa,echaricies, If we want to make better pepticies, ones that we can use to fight all types of infection, we need a more accurate molecular picture of how they \vork. This will hopefully be one step forward to the ( esign of better treatments for bacterial infections.
    • Magnetic and transport properties of (Ba1-xKx)Fe2As2

      Reuvekamp, Patrick.; Department of Physics (Brock University, 2009-01-28)
      Single crystals of (Bal - xKx)Fe2As2 were prepared using the Sn flux method. Two heating methods were used to prepare the single crystals: the slow heating and rapid heating methods. It was found that the single crystals grown using the slow heating method were not superconducting due to a significant loss of potassium. When the rapid heating method was used, the single crystals were observed to be superconducting with the desired potassium concentration. The energy dispersive X-ray spectroscopy analysis indicated the presence of multiple phases in the single crystals. Using single crystal X-ray diffraction, the crystal structure of the single crystals was found to be 14/mmm tetragonal at room temperature. The magnetic measurements on the single crystals indicated the presence of multiple phases and magnetic impurities.
    • Pressure dependence of superconductivity in amorphous Ni x Zr 100-x alloys

      Mahini Abyaneh, Fariba.; Department of Physics (Brock University, 1988-10-02)
      Pressure variations of the superconducting transition temperature Ic of a series of amorphous NixZr 1 OO-x alloys have been studied under quasmydrostatic pressures upto 8 G Pa. For amorphous samples having Ni-concentration less than 40%, i)Tc/dP is positive in sign and it decreases non linearly with increase in I. whereasdTcldP is negative in sign for Ni concentration of 45%. Comparison with the Hall coefficient (I) and the thermoelectric power (2) results for the same amorphous alloys leads to the conclusion that s-d hybridization nature of the d-band (Nil plays a central role in the sign reversal behaviour. Application of pressures greater than 2 G Pa to Ni20ZrgO led to the formation of a new phase, w-Zr. which retains its form after the pressure is released.
    • Far infrared spectroscopy of heavy fermion superconductor CeCoIn5 /

      Ocadlík, Stanislav.; Department of Physics (Brock University, 2004-07-14)
      The optical response to far infrared radiation has been measured on a mosaic of heavy fermion CeCoIns single crystals. The superconducting transition temperature of the crystals has been determined by van der Pauw resistivity and ac-susceptibility measurements as Tc = 2.3 K. The optical measurements were taken above and below the transition temperature using a ^He cryostat and step and integrate Martin-Puplett type polarizing interferometer. The absolute reflectance of the heavy fermion CeCoIns in the superconducting state in range (0, 100)cm~^ was calculated from the measured thermal reflectance, using the normal state data of Singley et al and a low frequency extrapolation for a metallic material in the Hagen-Rubens regime. By means of Kramers-Kronig analysis the absolute reflectance was used to calculate the optical conductivity of the sample. The real part of the calculated complex conductivity a{u)) of CeCoIns indicates a possible opening of an energy gap close to 50 cm~^.
    • The design of a reflectance spectrometer and its calibration using SrTiO3 /

      Klassen, J. Robert.; Department of Physics (Brock University, 2004-07-14)
      A new Ultra-High Vacuum (UHV) reflectance spectrometer was successfully designed, making use of a Janis Industries ST-400 sample cryostat, IR Labs bolometer, and Briiker IFS 66 v/S spectrometer. Two of the noteworthy features include an in situ gold evaporator and internal reference path, both of which allow for the experiment to progress with a completely undisturbed sample position. As tested, the system was designed to operate between 4.2 K and 325 K over a frequency range of 60 - 670 cm~^. This frequency range can easily be extended through the addition of appUcable detectors. Tests were performed on SrTiOa, a highly ionic incipient ferroelectric insulator with a well known reflectance. The presence and temperatmre dependence of the lowest frequency "soft" mode were measured, as was the presence of the other two infrared modes. During the structural phase transition from cubic to tetragonal perovskite, the splitting of the second phonon mode was also observed. All of the collected data indicate good agreement with previous measurements, with a minor discrepency between the actual and recorded sample temperatures.