CZUŁOŚĆ SPEKTROSKOPII MÖSSBAUEROWSKIEJ NA PRZEJŚCIE DO NADPRZEWODNICTWA

W Ba0.6K0.4Fe2As2

1Zakład Spektroskopii Mössbauerowskiej, Instytut Fizyki, Uniwersytet Pedagogiczny, Kraków, Polska2Instytut Niskich Temperatur i Badań Strukturalnych, Polska Akademia Nauk, Wrocław, Polska

3Cavendish Laboratory, University of Cambrige, United Kingdom4School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand

5Laboratory of Solid State Physics, ETH Zurich, Switzerland6Institute of Condensed Matter Physics, EPFL, Lausanne, Switzerland

A. K. Jasek1, K. Komędera1, A. Błachowski1, K. Ruebenbauer1, Z. Bukowski2, J. G. Storey3,4, J. Karpinski5,6

------------------------------------------------------------------------------------------------------X Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2014

Wrocław, 15-18 czerwca 2014

Tsc max = 56 K 47 K 18 K 15 K

Iron-based superconductor families

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

The aim of the experiment was to check whether the Mӧssbauer spectroscopy is sensitive to the superconducting transition in Ba0.6K0.4Fe2As2.

Ba1-xKxFe2As2

parent compound BaFe2As2

dopingK

superconductivityTsc=38K

Tetragonal unit cell of BaFe2As2 and phase diagram of Ba1-xKxFe2As2

Fig. 3. Lattice parameters of the series Ba1-xKxFe2As2 (x = 0–0.3)

Fig. 2. Resistivity of Ba1-xKxFe2As2 (x = 0.1-0.3)

Fig. 1. Resistivity of Ba0.6K0.4Fe2As2 plotted vs. temperature

BaFe2As2 vs. Ba0.6K0.4Fe2As2

Figs. 1,2. 57Fe Mössbauer spectra versus temperature forthe parent compound BaFe2As2 and the Ba0.6K0.4Fe2As2

Fig. 3. The difference in total molar specific heat coefficients

between superconductor (s) andparent compound (p) versus temperature

γtot=Ctot/T Ctot- the total molar heat capacity

totp

tots

The inset shows the electronic specific heat coefficient

of the superconductor versus temperature

Cel- the electronic molar heat capacity

TC elels /

Ba0.6K0.4Fe2As2 Tsc = 38 K

Selected Mössbauer spectra of the Ba0.6K0.4Fe2As2 across the transition to the superconducting state.Note the abrupt changes in the regions 40 K - 38 K and 28 K - 24 K

A. K. Jasek et al., J. Alloys Comp. 609, 150 (2014)

Parameters derived from the Mössbauer spectra of Ba0.6K0.4Fe2As2

plotted versus temperature.

S – total spectrum shift versus room temperature α-FeΔ0 – constant component of the quadrupole splitting Γ – absorber line widthtA – dimensionless absorber resonant thickness

Ratio of the recoilless fractions f/f0 and dispersion of CDW Δρ versus temperature

Electric field gradient wave (EFGW) in Ba0.6K0.4Fe2As2

Shape of EFGW )](sin[ )](cos[ )(

10

N

nnn nbna rqrqrq

)( )( 1max0 rqrq FAF

43

2 exp

41

2 exp )sin( )(

22

22

rqrqrqrqF

A - amplitude of EFGW

β - shape parameter of EFGW

- quadrupole coupling constant

Conclusions• CDW and modulation of the EFG on the iron nuclei develop within this

system.

• The new type of hyperfine interaction modulation called electric field gradient wave (EFGW) is seen on the iron nuclei.

• The charge modulation is sensitive to the transition between normal and superconducting state. CDW and EFGW strongly vary at the superconducting gap opening.

• A distribution of the “covalent” electrons is strongly perturbed by the itinerant electrons forming Cooper pairs.

• Dynamic properties of the iron nuclei seem unaffected by a transition to the superconducting state.

Thank You for Your attention