Evidence of a multiple boson emission in Sm1−xThxOFeAs

S. A. Kuzmichev; T. E. Kuzmicheva; N. D. Zhigadlo

doi:10.1209/0295-5075/119/17007

All issues

Volume 119 / No 1 (July 2017)

EPL, 119 1 (2017) 17007

Abstract

Issue		EPL Volume 119, Number 1, July 2017


Article Number		17007
Number of page(s)		7
Section		Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
DOI		https://doi.org/10.1209/0295-5075/119/17007
Published online		14 September 2017

EPL, 119 (2017) 17007

Evidence of a multiple boson emission in Sm_1−xTh_xOFeAs

S. A. Kuzmichev¹^,2, T. E. Kuzmicheva² and N. D. Zhigadlo³

¹ Department of Low Temperature Physics and Superconductivity, M.V. Lomonosov Moscow State University 119991 Moscow, Russia
² Laboratory of Strongly Correlated Electron Systems, P.N. Lebedev Physical Institute, Russian Academy of Sciences 119991 Moscow, Russia
³ Department of Chemistry and Biochemistry, University of Bern - Freiestrasse 3, CH-3012 Bern, Switzerland

Received: 1 June 2017
Accepted: 25 August 2017

Abstract

We studied a reproducible fine structure observed in dynamic conductance spectra of Andreev arrays in Sm_1−xTh_xOFeAs superconductors with various thorium concentrations ${(x = 0.08\text{--}0.3)}$ and critical temperatures $T_c = 26\text{--}50\ \text{K}$ . This structure is unambiguously caused by a multiple boson emission (of the same energy) during the process of multiple Andreev reflections. The directly determined energy of the bosonic mode reaches $\varepsilon_0 = 14.8 \pm 2.2\ \text{meV}$ for optimal compounds. Within the studied range of T_c, this energy as well as the large $\Delta_L$ and the small $\Delta_S$ superconducting gaps, nearly scale with critical temperature with the characteristic ratio $\varepsilon_0/k_BT_c \approx 3.2$ (and $2\Delta_L/k_BT_c \approx 5.3$ , respectively) resembling the expected energy $\Delta_L + \Delta_S$ of spin resonance and spectral density enhancement in $s^{\pm}$ and $s^{++}$ states, respectively.

PACS: 74.25.-q – Properties of superconductors / 74.45.+c – Proximity effects; Andreev reflection; SN and SNS junctions / 74.70.Xa – Pnictides and chalcogenides

© EPLA, 2017

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