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ABSTRACT: We report results of the ultrasonic investigation of Ba1-xKxBiO3 superconducting (SC) single crystals for two potassium concentrations x @ 0.35x \cong 0.35 and x @ 0.47x \cong 0.47 in a wide temperature range including the normal and the SC states. An instability of the crystal lattice that develops above
the superconducting phase transition leads to a softening of both the transverse c44 and the longitudinal c11 modes at temperatures between 200 K and 50 K. In the case of Ba0.65K0.35BiO3 a pronounced hysteresis was discovered. Low temperature X-ray powder diffraction analysis does not reveal any change of the
cubic structure in the samples within a resolution of our X-ray technique. The softening of the elastic moduli, the hysteresis,
the maximum in the attenuation of sound along with the possible short- (or long-) range structural distortion can be explained
qualitatively in a simple model by assuming a coupling of the acoustic modes with the anharmonic oscillations of BiO6 octahedra. Some weak anomalies are discovered in the velocity of the longitudinal sound in the vicinity of the superconducting
phase transition.
PACS. 62.65.+k Acoustical properties of solids - 74.72.-h High- compounds
Physics of Condensed Matter 04/2012; 16(1):59-66. · 1.53 Impact Factor
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ABSTRACT: We present for the first time ultrasonic velocity and attenuation measurements in pulsed magnetic fields up to 50 T. A quadrature method was used which allows us to measure velocity and attenuation changes simultaneously. To demonstrate this new experimental technique for pulsed field experiments we determine the elastic properties of the triangular antiferromagnet CsCuCl3. This substance exhibits different spin phases as a function of magnetic field showing spectacular effects in propagating sound waves. Our pulsed field experiments reveal new features of these magnetic phases.
EPL (Europhysics Letters) 01/2007; 48(2):182. · 2.17 Impact Factor
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ABSTRACT: We perform ultrasonic and ESR experiments up to 50 T in NH4CuCl3. As a function of temperature we find anomalies for the elastic constants c22 and c66 around the structural transition at 70 K. As a function of magnetic field we observe pronounced effects for these modes at the beginning and end of each magnetisation plateau. A linear relation of the c66 mode and the magnetic susceptibility is observed. The ESR modes follow a linear field dependence within the magnetic plateaus.
EPL (Europhysics Letters) 01/2007; 53(5):591. · 2.17 Impact Factor
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ABSTRACT: Temperature dependence of the elastic constants in the
superconducting state is described on the basis of the Ginsburg-Landau
theory. This approach shows very general character and allows to describe
quantitative renormalization of the elastic constants in the superconducting
state for different materials including non-conventional superconductors.
Various examples (A-15 compounds, Chevrel compounds, CeRu2,
Ba0.63K0.37BiO3, Yb3Rh4Sn13,
Ca3Rh4Sn13, HfV2, some heavy fermion compounds and
Sr2RuO4) are given.
Physics of Condensed Matter 06/2005; 46(2):169-176. · 1.53 Impact Factor
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ABSTRACT: SrCu2(BO3)(2) is a two-dimensional dimerized quantum spin system which is close to a quantum critical point. The sound velocity for the longitudinal and transverse acoustic modes shows strong spin-lattice effects. The shear c(66) mode exhibits a pronounced softening of 4.5% as a function of temperature and softens more than 25% in fields up to 50 T. This huge effect occurs in the vicinity of the magnetization plateaus m/m(0) = 1/4 and 1/3. We can analyze quantitatively the temperature dependence of all measured elastic modes c(11), c(44), and c(66) with an exchange striction mechanism. The soft c(66) mode with B(2g) symmetry enables us to predict the possible symmetry of the condensed triplets in some plateaus.
Physical Review Letters 06/2001; 86(21):4847-50. · 7.37 Impact Factor
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ABSTRACT: The crossing of the temperature dependences of sound velocity in the normal and the superconducting state of metallic glasses indicates renormalization of the intensity of sound interaction with two-level systems TLS's caused by their coupling with electrons. In this paper we examine different theoretical approaches to a quantitative description of the renormalization, using the results of a low-temperature ultrasonic investigation of Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 amorphous alloy. It is shown that the adiabatic renormalization of the coherent tunneling amplitude can explain only part of the whole effect observed in the experiment. There exists another mechanism of the renormalization affecting only nearly symmetric TLS's, which may be associated with the effect of electron density fluctuations on the interwell potential.
Physical Review B 09/2000; 62(10):6656. · 3.69 Impact Factor
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ABSTRACT: We present results on sound wave propagation in pulsed fields up to 50 T for CsCuCl <sub> 3 </sub> and (VO) <sub> 2 </sub> P <sub> 2 </sub> O <sub> 7 </sub>. Sound velocity and attenuation exhibit anomalies at the field induced spin transitions at low temperatures. In CsCuCl <sub> 3 </sub> we observe step-like anomalies in sound velocity and pronounced peaks in attenuation at the saturation field (34 T at 1.5 K) and broader anomalies at the commensurate-incommensurate transition (14–17 T). In (VO) <sub> 2 </sub> P <sub> 2 </sub> O <sub> 7 </sub> we observe a strong anomaly at the critical field when the lowest triplet branch crosses the singlet ground state (27 T at 1.6 K). All these experiments give important information on the spin state in high magnetic fields of these low dimensional spin systems and on the spin-phonon coupling. © 2000 American Institute of Physics.
Journal of Applied Physics 06/2000; · 2.17 Impact Factor
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ABSTRACT: The temperature and high magnetic field dependence of the longitudinal soundwave mode c_{11} in the two dimensional dimer system SrCu_{2}(BO_{3})_{2} is presented. c_{11}(T) shows anomalies due to strong interdimer spin-strain coupling. We can quantitatively interpret the temperature dependence of c_{11}(T) together with the magnetic susceptibility $\chi_{m}(T)$ with a molecular field approximation of coupled dimer triplets. The sound velocity up to 50T shows very sharp softening between the magnetization plateaus at low temperature. We argue that these pronounced effects arise from a resonant interaction between the phonons and the magnetic excitations which show softening between the plateaus.
05/2000;
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ABSTRACT: The crossing of temperature dependencies of sound velocity in the normal and the superconducting state of metallic glasses indicates renormalization of the intensity of sound interaction with two-level systems (TLS) caused by their coupling with electrons. In this paper we have analyzed different approaches to a quantitative description of renormalization using the results of low-temperature ultrasonic investigation of ZrTiCuNiBe amorphous alloy. It is shown that the adiabatic renormalization of the coherent tunneling amplitude can explain only part of the whole effect observed in the experiment. There exists another mechanism of renormalization affecting only nearly symmetric TLS. Comment: 10 pages, LaTeX, 6 Postscript figures, submitted to Phys. Rev. B
12/1999;
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ABSTRACT: Array of Josephson junctions with a nonsinusoidal current-phase relation as a model of the resistive transition of unconventional superconductors The superconducting energy gap and the parameter determining the intensity of electron scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the results of measurements of sound attenuation. The mechanism of adiabatic renormalization of the amplitude of coherent tunneling is used for a quantitative description of the peculiarities of sound absorption in the vicinity of T c .
Low Temperature Physics 12/1999; 25(12):1239. · 0.73 Impact Factor
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ABSTRACT: The crossing of temperature dependences of the sound velocity in normal and superconducting state of metallic glasses points out unambiguously the renormalization of the intensity of sound interaction with two-level systems (TLS), caused by their coupling with electrons. We propose a simple scenario which allows us to describe qualitatively the influence of the superconducting transition on the sound velocity and attenuation in superconducting metglasses and to make quantative estimations of renormalization parameters.
03/1998;
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B. Wolf,
C. Hinkel,
S. Holtmeier,
D. Wichert,
I. Kouroudis,
G. Bruls,
B. Lüthi,
M. Hedo,
Y. Inada,
E. Yamamoto,
Y. Haga,
Y. Onuki
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ABSTRACT: We present data of the elastic properties of the Laves phase compound CeRu2 in the normal and superconducting state obtained from ultrasound measurements. In the temperature range between the superconducting
transition temperature of 6.1 K and 300 K we used a deformation potential coupling approach to describe the temperature dependence
of the elastic constants. The elastic anomalies in the superconducting state are characterised with the model of thermally
assisted flux flow (TAFF). This enables us to construct a detailed superconducting B-T phase diagram including the vortex
dynamics and interpret the peak effect region. Especially the ultrasonic measurements exhibit clearly the connection between
the normal state and the superconducting properties. They show that structural fluctuations have strong effects on the superconductivity
and on the vortex dynamics.
Journal of Low Temperature Physics 04/1997; 107(3):421-441. · 1.19 Impact Factor
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ABSTRACT: Measurements of the elastic constants in the normal and superconducting state on a high quality URu2Si2 single crystal exhibit large anomalies in thec
11 mode versus temperature around 30 K andT
c. No such anomalies are visible in the c33 mode and in the shear elastic constants. We describe this behaviour with the anisotropic Grneisen parameter coupling. Using the c11 anomaly a B-T phase diagram is determined which clearly shows the single phase bulk properties of superconducting URu2Si2. The magnetic field dependences of the shear waves in the superconducting and normal state can be interpreted quantitatively with a Lorentz force mechanism.
Journal of Low Temperature Physics 01/1994; 94(3):307-324. · 1.19 Impact Factor
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ABSTRACT: A discussion of ultrasonic propagation in normal and superconducting heavy fermion systems is presented. In the normal state the temperature and magnetic field dependence of elastic constants is discussed. The regions of adiabatic and isothermal sound propagation are shown. In the superconducting state attenuation effects and B-T phase diagrams are discussed for different substances. The Grneisen parameters as the important electron-phonon coupling constants in the different phases are given and discussed.
Journal of Low Temperature Physics 01/1994; 95(1):257-270. · 1.19 Impact Factor
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ABSTRACT: In the antiferromagnetic heavy fermion superconductor URu2Si2 we observe the spin flop transition around 39 T below the Neel temperature TN using longitudinal sound. The c33-mode exhibits only one-step like anomaly at the spin flop transition in contrast to the three steps found in magnetization, magnetoresistance measurements and the longitudinal c11 mode. This behaviour can be explained using the Grüneisen parameter coupling for the field dependence of the elastic constants. Above the Neel temperature of 17.5 K we find a softening of the c33 elastic constants in high magnetic fields.
Journal of Magnetism and Magnetic Materials.
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ABSTRACT: We present elastic constant measurements of the heavy-fermion superconductor UPt3 at temperatures down to 50 mK and in static magnetic fields up to 30 T. These experiments yield information about the metamagnetic (MM) transition itself as a function of field as well as about the accompanying transitions as a function of temperature both above and below the critical field . A comparison is made with analogous measurements in CeRu2Si2. Moreover, we present new results on the region of the antiferromagnetic spin density wave (AF-SDW) in the B-T plane and its anisotropy with respect to the direction of the magnetic field. Here a comparison with the anisotropy of the superconducting critical fields gives clues about the interaction of superconductivity and magnetism in UPt3.
Physica B: Condensed Matter.
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The European Physical Journal B - Condensed Matter and Complex Systems. 16(1):59-66.
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ABSTRACT: We present measurements of the elastic constants for some of the known heavy fermion superconductors at low temperatures and high magnetic fields. In these compounds the superconducting phase lies embedded in another phase of more or less strongly magnetic nature. In contrast to the cases of UPt3, URu2Si2 and UPd2Al3 where the superconductivity coexists with antiferromagnetic order, our results indicate that in high quality CeCu2Si2 single crystals the superconductivity does not coexist with the embedded phase but rather expels it. The influence of the Cu stoichiometry on the physical properties and on the B-T phase diagram of CeCu2Si2 is discussed. In addition we find pronounced elastic anomalies in magnetic fields up to 23 T, which yield a detailed B-T phase diagram for CeCu2Si2. By comparison with results obtained with other methods we gain information about the nature of various transitions. Further we show magnetoacoustic quantum oscillations (MAQO) and other magnetoacoustic effects in the heavy fermion superconductors.
Physica B: Condensed Matter.
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ABSTRACT: We present high magnetic field ultrasonic and magnetic susceptibility measurements for Nd2CuO4 and Nd1.85Ce0.15CuO4 single crystals at temperatures below 2 K. The magnetic field dependences of the c11, c66 acoustic modes and the magnetic susceptibility demonstrate a large number of field induced phase transitions which are reduced in the Ce-doped compound. Using the anomalies in the sound velocity and magnetic susceptibility we obtained the low temperature range of B–T phase diagrams of these compounds for magnetic field applied along the [100] direction.
Physica B: Condensed Matter.
