Strong Correlations, Strong Coupling and s-wave Superconductivity in Hole-doped BaFe2As2 Single Crystals

Abstract

We present a comprehensive study of the low-temperature heat capacity and thermal expansion of single crystals of the hole-doped Ba1-xKxFe2As2 series (0<x<1) and the end-members RbFe2As2 and CsFe2As2. A large increase of the Sommerfeld coefficient is observed with both decreasing band filling and isovalent substitution (K, Rb, Cs) revealing a strong enhancement of electron correlations and the possible proximity of these materials to a Mott insulator. This trend is well reproduced theoretically by our Density-Functional Theory + Slave-Spin (DFT+SS) calculations, confirming that 122-iron pnictides are effectively Hund metals, in which sizable Hund's coupling and orbital selectivity are the key ingredients for tuning correlations. We also find direct evidence for the existence of a coherence-incoherence crossover between a low-temperature heavy Fermi liquid and a highly incoherent high-temperature regime similar to heavy fermion systems. In the superconducting state, clear signatures of multiband superconductivity are observed with no evidence for nodes in the energy gaps, ruling out the existence of a doping-induced change of symmetry (from s to d-wave). We argue that the disappearance of the electron band in the range 0.4<x<1.0 is accompanied by a strong-to-weak coupling crossover and that this shallow band remains involved in the superconducting pairing, although its contribution to the normal state fades away. Differences between hole- and electron-doped BaFe2As2 series are emphasized and discussed in terms of strong pair breaking by potential scatterers beyond the Born limit.

Submitted to Phys. Rev. B

References in corpus (26)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Unconventional pairing originating from disconnected Fermi surfaces in superconducting LaFeAsO${}_{1-x}$F${}_x$}
• Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2
• Strong electronic correlations from Hund's coupling
• Coherence-incoherence crossover in the normal state of iron-oxypnictides and importance of the Hund's rule coupling
• Orbital selective Mott transition in multi-band systems: slave-spin representation and dynamical mean-field theory
• Iron based superconductors: magnetism, superconductivity and electronic structure
• Momentum dependence of the superconducting gap in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$
• Pairing State with a time-reversal symmetry breaking in FeAs based superconductors
• Superfluid density of the $\pm$s-wave state for the iron-based superconductors
• Importance of Fermi surface topology for high temperature superconductivity in electron-doped iron arsenic superconductors
• Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
• Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAs
• Enhancement of $T_c$ by disorder in underdoped iron pnictides
• Evidence of a spin resonance mode in the iron-based superconductor Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ from scanning tunneling spectroscopy
• Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy
• Effect of annealing on the specific heat of Ba(Fe1-xCox)2As2
• Heat transport in RbFe2As2 single crystal: evidence for nodal superconducting gap
• Universal pair-breaking in transition metal-substituted iron-pnictide superconductors
• Crossover in the magnetic response of single-crystalline Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ and Lifshitz critical point evidenced by Hall effect measurements
• Specific Heat Discontinuity DeltaC vs Tc in Annealed Ba(Fe1-xCox)2As2
• Single Impurity Effects in Multiband Superconductors with Different Sign Order Parameters
• Anomalous density of states in multiband superconductors near Lifshitz transition
• Superconducting properties of (Ba-K)Fe2As2 single crystals disordered with fast neutron irradiation
• Cooper Pairing in Insulating Valence Band in Fe-Based Superconductors
• Superconductivity In K- And Na- Doped Bafe2as2: What Can We Learn From Heat Capacity And Pressure Dependence of Tc

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• PhD Thesis: Electronic correlations in multiorbital systems