Nadprzewodniki na bazie żelaza w świetle badań metodą spektroskopii mössbauerowskiej Artur Błachowski1, Kamila Komędera1, Krzysztof Ruebenbauer1, Jan Żukrowski2 1 Laboratorium Spektroskopii Mössbauerowskiej, Instytut Fizyki, Uniwersytet Pedagogiczny, ul. Podchorążych 2, 30-084 Kraków 2 Akademickie Centrum Materiałów i Nanotechnologii, Akademia Górniczo-Hutnicza, al. Mickiewicza 30, 30-059 Kraków ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

• H2S • FeSe s-l Up to now the maximum Tsc is 56 K 155 GPa Published on Web 02/23/2008

Fe-based Superconducting Families pnictogens: P, As chalcogens: S, Se, Te 1111 122 111 11 LnO(F)FeAs AFe2As2 AFeAs FeTe(Se,S) Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li , Na Tsc max = 56 K 47 K 18 K 15 K

Layered Structure of Fe-based Superconductors Spin density wave (SDW) magnetic order --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Phase Diagram Holes, electrons or isovalent doping BaFe2As2 Ba1-xKxFe2As2 BaFe2-xCoxAs2 BaFe2As2-xPx Parent Compounds SDW Doped Compounds  Superconductors

Mössbauer Spectroscopy -ray energy is modulated by the Doppler effect due to the source motion vs. absorber Source (e.g. 57Co/Rh) Absorber (57Fe) Detector – v +v 1 mm/s  48 neV

Hyperfine Interactions between Nuclei and Electrons  Mössbauer Parameters Electric Monopole Interaction  Isomer Shift Electric Quadrupole Interaction  Quadrupole Splitting Magnetic Dipole Interaction  Magnetic Splitting

Charge density wave (CDW) Electric field gradient wave (EFGW) - spatial modulation of the electron charge density Electric field gradient wave (EFGW) - spatial modulation of the electric field gradient The Mössbauer spectroscopy is sensitive to the charge (electron) distribution around the resonant nucleus via the isomer shift and the electric quadrupole interaction.

Charge density wave (CDW) as seen by Mössbauer Spectroscopy Construction of Mӧssbauer spectrum for sinusoidal CDW (a) one period of CDW (b) partial sub-spectra having the isomer shift proportional to amplitude of CDW (c) the overall spectrum (d) histogram of the isomer shift (charge-density) distribution. J.Cieślak, S.M.Dubiel, Nuclear Instr. Methods B 101, 295 (1995) In our case - A signature of CDW is seen as the excess of the absorber line width. One can estimate variation (dispersion) of the electron density  on the resonant nuclei (around average value) caused by existing CDW. Γ – absorber line width – unbroadened line width – calibration constant

Electric field gradient wave (EFGW) as seen by Mössbauer Spectroscopy  - quadrupole coupling constant with 57Fe Mössbauer spectra Distributions of quadrupole shift Shape of EFGW

Mössbauer Spectroscopy Laboratory, Pedagogical University, Kraków, Poland dr Aleksandra Jasek mgr Kamila Komędera doktorantka, IV rok

Ba1-xKxFe2As2 parent compound BaFe2As2 doping K superconductor Tsc = 38K Tetragonal unit cell and phase diagram of Ba1-xKxFe2As2 12

57Fe Mössbauer spectra A.K.Jasek, K.Komędera, A.Błachowski, K.Ruebenbauer, Z.Bukowski, J.G.Storey, J.Karpinski, J. Alloys Compd. 609, 150 (2014) Difference in total molar specific heat coefficients between superconductor and parent compound. Inset shows electronic specific heat coefficient of superconductor. 13

57Fe Mössbauer spectra of the Ba0.6K0.4Fe2As2 (TSC = 38 K) across transition to the superconducting state. Difference in total molar specific heat coefficients between superconductor and parent compound. Inset shows electronic specific heat coefficient of superconductor.

Ba0.6K0.4Fe2As2 (TSC = 38 K) Shape of EFGW electric field gradient wave (d electrons density variation) Mössbauer spectra parameters S – total spectrum shift versus α-Fe Δ0 – constant component of quadrupole splitting Γ – absorber line width tA – dimensionless absorber resonant thickness Relative recoilless fraction f/f0 (normalized to f0 at 4.2 K) Dispersion of CDW charge density wave (s electrons density variation)

parent compound SmFeAsO doping F superconductivity Tsc = 55K SmFeAsO1-xFx parent compound SmFeAsO doping F superconductivity Tsc = 55K Związek macierzysty SmFeAsO nadprzewodnika należącego do rodziny 1111. Tlen i samar wprowadzają szerszą przestrzeń pomiędzy warstwami arsenowo-żelazowymi. W badanej próbce część tlenu została zastąpiona fluorem. W temperaturze pokojowej układ krystalizuje w strukturze tetragonalnej. Wraz z obniżaniem temperatury w okolicach 150 K związek ulega dystorsji strukturalnej do struktury rombowej i pojawia się porządek magnetyczny typu fali gęstości spinowej. Dodając domieszki fluoru (𝑥) w miejsce atomów tlenu tłumi moment magnetyczny na jądrach żelaza i w okolicach 4 % domieszki pojawia się stan nadprzewodnictwa. Zgodnie z diagramem fazowym w badanej przeze mnie próbce powinien współistnieć stanu uporządkowania magnetycznego oraz stan nadprzewodnictwa (?) Tetragonal unit cell of SmFeAsO Phase diagram of SmFeAsO1-xFx A.J. Drew et al., Nature Materials 8, 310 (2009) Y. Kamihara et al., New J. Phys. 12, 033005 (2010) our sample – SmFeAsO0.91F0.09 16

SmFeAsO0.91F0.09 Tsc  47 K Resistivity and magnetic susceptibility 57Fe Mössbauer spectroscopy magnetic spectral broadening below 28 K A.K.Jasek, K.Komędera, A.Błachowski, K.Ruebenbauer, H.Lochmajer, N.D.Zhigadlo, and K.Rogacki, J. Alloys Compd. 658, 520 (2016)

57Fe Mössbauer spectra of SmFeAsO0.91F0.09 (Tsc ≈ 47 K) across transition to the superconducting state Resistivity Magnetic susceptibility

SmFeAsO0.91F0.09 (Tsc ≈ 47 K) Mössbauer spectra parameters Shape of EFGW electric field gradient wave (d electrons density variation) Relative recoilless fraction f/f0 (normalized to f0 at 28 K) Dispersion of CDW charge density wave (s electrons density variation)

charge density modulation changes during superconducting transition in Comparison between charge density modulation changes during superconducting transition in Ba0.6K0.4Fe2As2 (hole doping) SmFeAsO0.91F0.09 (electron doping) EFGW EFGW CDW CDW  K

Conclusions References Ba1-xKxFe2As2 and SmFeAsO1-xFx The Mössbauer spectroscopy is sensitive to the superconducting transition in Fe-based superconductors via change of the electron charge density modulation, which is seen via dispersion of isomer shift (CDW caused by s electrons) and via distribution of electric field gradient (EFGW caused by d electrons). Shape and amplitude of EFGW and CDW are strongly perturbed at the superconducting transition. Namely, all modulations are strongly changed at critical temperature due to the superconducting gap opening and subsequent formation of Cooper pairs. However dispersion of the charge density and EFGW shape behave in the opposite ways for these two superconductors. References A.K.Jasek, K.Komędera, A.Błachowski, K.Ruebenbauer, Z.Bukowski, J.G.Storey, J.Karpinski, Electric field gradient wave (EFGW) in iron-based superconductor Ba0.6K0.4Fe2As2 studied by Mössbauer spectroscopy, J. Alloys Compd. 609, 150 (2014) A.K.Jasek, K.Komędera, A.Błachowski, K.Ruebenbauer, H.Lochmajer, N.D.Zhigadlo, K.Rogacki, Change of the charge modulation during superconducting transition in SmFeAsO0.91F0.09 seen by 57Fe Mössbauer spectroscopy, J. Alloys Compd. 658, 520 (2016)