Normal-state properties of the antiperovskite oxide Sr3−xSnO revealed by Sn119 -NMR

Abstract

We have performed 119 Sn-NMR measurements on the antiperovskite oxide superconductor Sr 3−x SnO to investigate how its normal state changes with the Sr deficiency. A two-peak structure was observed in the NMR spectra of all the measured samples. This suggests that the phase separation tends to occur between the nearly stoichiometric and heavily Sr-deficient Sr 3−x SnO phases. The measurement of the nuclear spin-lattice relaxation rate 1/T 1 indicates that the Sr-deficient phase shows a conventional metallic behavior due to the heavy hole doping. In contrast, the nearly stoichiometric phase exhibits unusual temperature dependence of 1/T 1 , attributable to the presence of a Dirac-electron band.

Negative ionic states of tin in the oxide superconductor Sr3−xSnO revealed by Mössbauer spectroscopy

“…The present results confirm the Sn 4state and thus the validity of the band structure calculations. In this sense, these results are consistent with the NMR experiments observing the 1/T 1 attributable to the Dirac dispersion [15]. Furthermore, since the large amount of the Sr deficiency to "Sr 3 Sn 2 O 2 " or "Sr 2 Sn 2 O 2 " leads to heavy hole doping, the deficient phase with a large portion of such Sn sites with neighboring Sr deficiency would exhibit metallic 1/T 1 , as indeed observed in the NMR measurements.…”

“…We comment that the phase splitting into the nearly stoichiometric and deficient compounds has been suggested in the previous study of magnetization [16] and indeed observed with NMR [15]. Since NMR probes properties of the conduction electrons though it measures the Zeeman energy of the Sn nucleus, the splitting in the NMR spectrum suggests that one sample consists of two materials ("phases") with distinct stoichiometries as shown in Fig.…”

“…The metallic anion Sn 4was experimentally observed in Sr 3 SnO using the Mössbauer spectroscopy at room temperature by some of the present authors [16]. The Dirac cone in the bulk band structure is confirmed in Ca 3 PbO with the angle-resolved photoemission spectroscopy (ARPES) [9], in Sr 3 PbO with magnetotransport [13], and in Sr 3 SnO with nuclear magnetic resonance (NMR) [15]. Furthermore, thermoelectric properties of * a.ikeda@scphys.kyoto-u.ac.jp Ca 3 SnO and Ca 3 Pb 1x Bi x O are studied to make use of the multivalley band structure with six equivalent Dirac cones [7].…”

“…This material exhibits two superconducting transitions at T c 5 K and 0.8 K. Theoretical analyses indicate that the superconductivity in Sr 3x SnO can be topological crystalline superconductivity with j = 3/2 pairing reflecting the topology of the electronic band structure in the normal state [8,14]. Band structure calculations [11] and NMR experiments [15] suggest heavy hole doping to Sn due to Sr deficiency. Indeed, Mössbauer spectra at room temperature revealed additional ionic state of Sn having less electrons than Sn 4 -, and its fraction increases with Sr deficiency [16].…”

“…Due to the recent predictions of bulk Dirac cones [3,4] and topological nature [5] in the vicinity of the Fermi energy, antiperovskite oxides are attracting a lot of attention [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. After the initial theoretical predictions, the chemical and physical characters of antiperovskite oxides have been extensively investigated [6].…”