Structural phase transition, precursory electronic anomaly, and strong-coupling superconductivity in quasi-skutterudite (Sr _{1− x} Ca _x ) ₃ Ir ₄ Sn ₁₃

Abstract

The interplay between superconductivity and structural phase transition has attracted enormous interest in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr 1−x Ca x ) 3 Ir 4 Sn 13 (x = 0, 0.5, 1) and Ca 3 Rh 4 Sn 13 show some unusual properties similar to the Fe-pnictides, through 119 Sn nuclear magnetic resonance (NMR) measurements. In (Sr 1−x Ca x ) 3 Ir 4 Sn 13 , the NMR linewidth increases below a temperature T * that is higher than the structural phase transition temperature T s . The spin-lattice relaxation rate (1/T 1 ) divided by temperature (T ), 1/T 1 T and the Knight shift K increase with decreasing T down to T * , but start to decrease below T * , and followed by more distinct changes at T s . In contrast, none of the anomalies is observed in Ca 3 Rh 4 Sn 13 that does not undergo a structural phase transition. The precursory phenomenon above the structural phase transition resembles that occurring in Fe-pnictides. In the superconducting state of Ca 3 Ir 4 Sn 13 , 1/T 1 decays as exp(−∆ /k B T ) with a large gap ∆ = 2.21k B T c , yet without a Hebel-Slichter coherence peak, which indicates strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.

Possible unconventional pairing in $(\text{Ca,Sr})_{3}(\text{Ir,Rh})_{4}\text{Sn}_{13}$ superconductors revealed by controlling disorder

“…The temperature dependent electrical resistivity for Sr 3 Ir 4 Sn 13 and its evolution with electron irradiation are shown in the main panel of Figure 3. The resistivity value for the selected sample of Sr 3 Ir 4 Sn 13 is in reasonable agreement with previous reports of 120 µΩ• cm [53,55]. Irradiation shifts the ρ(T ) curves upward at high temperatures, but they remain nearly parallel to each other above T CDW .…”

“…Heat capacity measurements find exponential decrease at the low temperatures [52] and a linear field-dependence [53], which also agrees with a full-gap superconducting state. There are signs of strong coupling superconductivity in heat capacity measurements around the QCP [54,55,57]. µSR experiments under pressure find that the superfluid density strongly increases when pressure is tuned close to the QCP in Ca 3 Ir 4 Sn 13 [57].…”

Fully gapped spin-singlet superconductivity in noncentrosymmetricPbTaSe2:Pb207nuclear magnetic resonance study

“…First of all, non s-wave superconducting state produces no coherence peak. Even in an s-wave superconductor, the height of the coherence peak can be suppressed by many factors such as a large applied magnetic field, anisotropy of superconducting gap 37 , multiple superconducting gaps 38 , large nuclear electric quadrupole moment 39 , and phonon damping in the strong coupling regime 41,42 . Since 2∆ = 3.5 k B T c indicates a weak-coupling superconductor, phonon damping is unlikely as a origin.…”

Nonmagnetic ground state, Crystal field effects and Heavy-fermion behaviour in the Remeika Phase: Pr$_3$Ir$_4$Ge$_{13}$

“…The X' atom at 2a site exhibits ionic character, whereas the X atom at 24k shows a metallic bonding character, hence the general stoichiometry formula is seldom written as X'A 3 T 4 X 12 instead of A 3 T 4 X 13 [2]. More than 120 compounds have been reported in the literature that are exhibiting some exotic states of matter ranging from heavy-fermion state [4,5], intermediate valence behaviour [6], superconductivity [7,8], charge density wave order [9], itinerant ferromagnetism [10], and quantum criticality [11]. Among various classes, Tin containing compounds are extensively studied due to the interplay between structural, magnetic and superconducting properties.…”

“…Among various classes, Tin containing compounds are extensively studied due to the interplay between structural, magnetic and superconducting properties. For example, (Ca, Sr) 3 Ir 4 Sn 13 exhibit charged density wave order at T = 33 K and 138 K respectively and the transition temperature can be suppressed by chemical or physical pressure to drive the system close to a quantum critical point [12,11]. Another interesting stannide based compound is Ce 3 Co 4 Sn 13 which shows complicated semiconducting property and exhibits single channel single ion impurity Kondo effect with T K (Kondo temperature) = 1.5 K [13,14].…”