“…When compared to the phase diagram previously known in NaFe 1− x A x As ( A = Co, Cu, or Rh) 23, 24, 39, 40 , a difference is the seeming mutual repulsion of the SDW and bulk superconductivity near x c ~ 0.03, similar to that reported in LaFeAsO 1− x F x 41 and NaFe 1− x Co x As 42 . However, our data are not sufficiently dense to conclude whether the SDW and SC phases coexist in the narrow doping range near x = 0.03 or completely repel each other.Fig.…”
Section: Resultssupporting
confidence: 74%
“…1c) decreases abruptly, allowing us to assign T c from χ , ~ 7.0 K. These transport and magnetization data are overall consistent with those found in previous reports on NaFeAs (refs. 19–24 ).…”
Section: Resultsmentioning
confidence: 99%
“…In other doped Na 111 systems like NaFe 1− x Co x As 22 and NaFe 1− x Rh x As 24 , robust metallic behavior were observed in broad doping ranges. The former Cu doping was claimed to have isoelectronic doping while the latter two involving large electron doping was inevitably accompanied by large chemical potential shift.…”
Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1−xLixFeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs.
“…When compared to the phase diagram previously known in NaFe 1− x A x As ( A = Co, Cu, or Rh) 23, 24, 39, 40 , a difference is the seeming mutual repulsion of the SDW and bulk superconductivity near x c ~ 0.03, similar to that reported in LaFeAsO 1− x F x 41 and NaFe 1− x Co x As 42 . However, our data are not sufficiently dense to conclude whether the SDW and SC phases coexist in the narrow doping range near x = 0.03 or completely repel each other.Fig.…”
Section: Resultssupporting
confidence: 74%
“…1c) decreases abruptly, allowing us to assign T c from χ , ~ 7.0 K. These transport and magnetization data are overall consistent with those found in previous reports on NaFeAs (refs. 19–24 ).…”
Section: Resultsmentioning
confidence: 99%
“…In other doped Na 111 systems like NaFe 1− x Co x As 22 and NaFe 1− x Rh x As 24 , robust metallic behavior were observed in broad doping ranges. The former Cu doping was claimed to have isoelectronic doping while the latter two involving large electron doping was inevitably accompanied by large chemical potential shift.…”
Strong interplay of spin and charge/orbital degrees of freedom is the fundamental characteristic of the iron-based superconductors (FeSCs), which leads to the emergence of a nematic state as a rule in the vicinity of the antiferromagnetic state. Despite intense debate for many years, however, whether nematicity is driven by spin or orbital fluctuations remains unsettled. Here, by use of transport, magnetization, and 75As nuclear magnetic resonance (NMR) measurements, we show a striking transformation of the relationship between nematicity and spin fluctuations (SFs) in Na1−xLixFeAs; For x ≤ 0.02, the nematic transition promotes SFs. In contrast, for x ≥ 0.03, the system undergoes a non-magnetic phase transition at a temperature T0 into a distinct nematic state that suppresses SFs. Such a drastic change of the spin fluctuation spectrum associated with nematicity by small doping is highly unusual, and provides insights into the origin and nature of nematicity in FeSCs.
“…Single crystals were grown using the self-flux technique [25,26]. ARPES measurements were conducted at the 1 2 -and 1 3 -ARPES endstations attached to the beamline UE112 PGM 2 at BESSY with energy and angle resolutions between 4 and 10 meV and 0.2…”
Angle-resolved photoemission spectroscopy is used to study the band dispersion and the quasiparticle scattering rates in two ferropnictide systems. We find the scattering rate for any given band to depend linearly on energy but to be independent of the control parameter. We demonstrate that the linear energy dependence gives rise to a weakly dispersing band with a strong mass enhancement when the band maximum crosses the chemical potential. The resulting small effective Fermi energy favors a BCS [J. Bardeen et al., Phys. Rev. 108, 1175(1957] -Bose-Einstein [S. N. Bose, Z. Phys. 26, 178 (1924)] crossover state in the superconducting phase.
“…Single crystals of and were grown in Göttingen and Augsburg using the Sn‐flux and the Bridgman (without Sn flux) method, respectively, and they were characterized by various methods (). Single crystals of and were grown in Dresden using as well the self‐flux method ().…”
In this article, we review our angle- and time-resolved photoemission studies (ARPES and trARPES) on various ferropnictides. In the ARPES studies, we focus first on the band structure as a function of control parameters. We find near optimally “doped” compounds a Lifshitz transition of hole/electron pocket vanishing type. Second, we investigated the inelastic scattering rates as a function of the control parameter. In contrast to the heavily discussed quantum critical scenario, we find no enhancement of the scattering rate near optimally “doping.” Correlation effects which show up by the non-Fermi-liquid behavior of the scattering rates, together with the Lifshitz transition offer a new explanation for the strange normal state properties and suggests an interpolating superconducting state between BCS and BE condensation. Adding femtosecond time resolution to ARPES provides complementary information on electron and lattice dynamics. We report on the response of the chemical potential by a collective periodic variation coupled to coherent optical phonons in combination with incoherent electron and phonon dynamics described by a three temperature heat bath model. We quantify electron phonon coupling in terms of λ(ω2) and show that the analysis of the electron excess energy relaxation is a robust approach. The spin density wave ordering leads to a pronounced momentum dependent relaxation dynamics. In the vicinity of kF, hot electrons dissipate their energy by electron–phonon coupling with a characteristic time constant of 200 fs. Electrons at the center of the hole pocket exhibit a four time slower relaxation which is explained by spin-dependent dynamics with its smaller relaxation phase space. This finding has implications beyond the material class of Fe-pnictides because it establishes experimental access to spin-dependent dynamics in materials with spin density waves
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