Second-order Structural Transition in (Ca0.5Sr0.5)3Rh4Sn13 (original) (raw)
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Heavy-electron behavior and structural change in Ca1. 7Sr0. 3RuO4
Arxiv preprint cond-mat/ …, 2001
Sr2RuO4 is an unconventional superconductor with a tetragonal structure, whereas Ca2RuO4 is a Mott insulator with orthorhombic symmetry. The substituted Ca2−xSrxRuO4 has yielded a rich phase diagram that is just beginning to be explored in detail. Experimental investigation of the resistivity ρ, susceptibility χ, specific heat Cp, Hall coefficient RH, and X-ray diffraction of Ca1.7Sr0.3RuO4 reveals a structural phase transition near T0 = 190 K and heavy-Fermion (HF) behavior below a coherence temperature T * ∼ 10 K, resembling that of the f-electron HF compound UPt3. The observation of T 2-dependence of ρ below ∼ 0.5 K suggests a Fermi-liquid ground state. Based upon our data and theoretical calculations, we argue that the structural change at T0 may be responsible for the formation of the HF state.
Exotic phase transitions in RERhSn compounds
Nukleonika, 2003
Crystal and magnetic properties of three equiatomic ternary RERhSn compounds (where RE = Ce, Nd, Gd) have been studied by means of X-ray diffraction, ac, and dc magnetic susceptibility measurements, as well as using Mössbauer spectroscopy with 119 Sn and 155 Gd resonances. CeRhSn does not order magnetically down to 2 K while NdRhSn undergoes ferromagnetic transition at T C = 10.3 K and GdRhSn orders antiferromagnetically below T N = 16 K. Our CeRhSn and NdRhSn samples become superconductive below 6.5 K and 6.9 K, respectively.
Two distinct structural phases in Sr3?x Ca x Ru2O y
Journal of Low Temperature Physics, 1996
Wehavesynthesized anew bilayered ruthenate solid solution Sr3-x Ca x Ru 2 0 7 (0$t~2.0), which is homologous to copper-free layered perovskite superconductor Sr 2 Ru0 4 (Tc =1.5 K), with the aim of searching for new superconductors. We have also succeeded in growing single crystals of Sr 3 Ru 2 0 7 by a floating zone (FZ) method. A systematic measurement has been carried out for the x dependence of the lattice parameters, magnetic susceptibility X(1), magnetization M(H), and electrical resistivity AT). No indication of superconductivity has been observed down to 100 mK for x=O (single crystals), 300 mK for x=l, and 2 K for other compositions. The measured values of lattice parameters and of magnetic quantities for the present single crystal samples are in good agreement with those for polycrystalline samples. Polycrystalline samples for 0.6<x~2.0 show magnetic ordering below 50 K. It is intriguing that the magnetic correlations vary with increasing Ca content, from nearly ferromagnetic, to itinerant weakly ferromagnetic, and finally to localized antiferromagnetic. For x(Ca)=O, we have concluded that the ground state is the strongly-correlated Fermi liquid accompanied by enhanced ferromagnetic correlations. The lowest magnetic ordering temperature in this series is observed at 3.2 K in the sample with x (Ca) =1.0. This transition is described well as that due to a weakly ferromagnetic ordering by the self-consistent renormalization (SCR) theory of spin fluctuations. To the best of our knowledge, this is the first example to demonstrate an applicability of the SCR theory to a weak ferromagnet with a quasi-two dimensional crystal structure.
We show that the quasi-skutterudite superconductor Sr3Ir4Sn13 undergoes a structural transition from a simple cubic parent structure, the I-phase, to a superlattice variant, the I-phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T * can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.
Crystal structure and phonon softening in Ca3Ir4Sn13
Physical Review B
We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T > T* ≈ 38 K, the x-ray diffraction data can be satisfactorily refined using the space group Pm-3n. Below T*, the crystal structure is modulated with a propagation vector of q =(1/2,1/2,0). This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Δ(120 K) = 1.05 meV. Using density functional theory, the soft phonon mode is identified as a “breathing” mode of the Sn12 icosahedra and is consistent...
2012
We show that the quasi-skutterudite superconductor Sr_3Ir_4Sn_13 undergoes a structural transition from a simple cubic parent structure, the I-phase, to a superlattice variant, the I'-phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature T* can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.
Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019), 2020
Successive phase transitions of R 3 Ir 4 Sn 13 (R: La and Ce) were studied using neutron and x-ray diffraction techniques. A semimetal Ce 3 Ir 4 Sn 13 undergoes three phase transitions: an antiferromagnetic ordering characterized by a propagation vector q M = (1/2, 1/2, 2/5) below 0.6 K, a structural transformation with q S2 = (1/4, 1/4, 1/4) at 2.0 K, and another structural transformation with q S1 = (1/2, 1/2, 0) above room temperature. La 3 Ir 4 Sn 13 was confirmed to be a superconductor below 2.5 K under the q S1 = (1/2, 1/2, 0) structure that also appears above room temperature.
Phonon softening and anomalous mode near the xc=0.5 quantum critical point in Ca2−xSrxRuO4
Physical Review B, 2009
Inelastic neutron scattering is used to measure the temperature-dependent phonon dispersion in Ca 2−x Sr x RuO 4 ͑x = 0.4, 0.6͒. The in-plane ⌺ 4 octahedral tilt mode softens significantly at the zone boundary of the high-temperature tetragonal ͑HTT͒ I4 1 / acd structure as the temperature approaches the transition to a low-temperature orthorhombic ͑LTO͒ Pbca phase. This behavior is similar to that in La 2 CuO 4 , but an inelastic feature that is not found in the cuprate is present. An anomalous phonon mode is observed at energy transfers greater than the ⌺ 4 , albeit with similar dispersion. This anomalous phonon mode never softens below ϳ5 meV, even for temperatures below the HTT-LTO transition. This mode is attributed to the presence of intrinsic structural disorder within the I4 1 / acd tetragonal structure of the doped ruthenate.
Experimental Study of the Ca Effect in the Cubic-Tetragonal Phase Transition of Ca1-xSrxTiO3
Ferroelectrics, 2004
Theentropyexcesscorrespondingto the cubic to tetragonal transition in Ca 0.04 Sr 0.96 TiO 3 perovskite has been obtained by integration of specific heat measured by conduction calorimetry. The order parameter of the transition has been obtained by means of neutron diffraction at low temperatures. Comparison of calorimetric data with the evolution of the order parameter indicates that this transition follows a mean field Landau potential as in SrTiO 3. The linear behaviour of the excess of entropy versus temperature suggests that a 2-4 Landau potential is sufficient to describe the transition. The Ca effect in thermodinamical properties of SrTiO 3 is compared with the effect of an uniaxial stress applied on pure SrTiO 3 .
Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo 2 As 2
In tetragonal SrCo2As2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [W. Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe2As2 (A = Ca, Sr, Ba) parent compounds of high-Tc superconductors. This surprising discovery suggests that SrCo2As2 may also be a good parent compound for high-Tc superconductivity. Here, structural and thermal expansion, electrical resistivity ρ, angle-resolved photoemission spectroscopy (ARPES), heat capacity Cp, magnetic susceptibility χ, 75 As NMR and neutron diffraction measurements of SrCo2As2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient αc is negative from 7 to 300 K, whereas αa (the a-axis thermal expansion coefficient) is positive over this T range. The ρ(T ) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy EF. The band calculations exhibit an extremely sharp peak in the density of states D(E ≈ EF) arising from a flat d x 2 −y 2 band, where the x and y axes are along the a and b axes of the Co square lattice, respectively. A comparison of the Sommerfeld coefficient of the electronic specific heat with χ(T → 0) suggests the presence of strong ferromagnetic itinerant spin correlations which on the basis of the Stoner criterion predicts that SrCo2As2 should be an itinerant ferromagnet, in conflict with the magnetization data. The χ(T ) does have a large magnitude, but also exhibits a broad maximum at ≈ 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we suggest that metallic SrCo2As2 has a gapless quantum spin-liquid ground state.