Iron pnictides as a new setting for quantum criticality

Abstract

Two major themes in the physics of condensed matter are quantum critical phenomena and unconventional superconductivity. These usually occur in the context of competing interactions in systems of strongly-correlated electrons. All this interesting physics comes together in the behavior of the recently discovered iron pnictide compounds that have generated enormous interest because of their moderately high-temperature superconductivity. The ubiquity of antiferromagnetic ordering in their phase diagrams naturally raises the question of the relevance of magnetic quantum criticality, but the answer remains uncertain both theoretically and experimentally. Here we show that the undoped iron pnictides feature a novel type of magnetic quantum critical point, which results from a competition between electronic localization and itinerancy. Our theory provides a mechanism to understand the experimentally-observed variation of the ordered moment among the undoped iron pnictides. We suggest P substitution for As in the undoped iron pnictides as a means to access this new example of magnetic quantum criticality in an unmasked fashion. Our findings point to the iron pnictides as a much-needed new setting for quantum criticality, one that offers a new set of control parameters.Comment: (v3) New abstract, more explanatory material, accepted for PNA

Magnetic phase diagram of an extendedJ1−J2model on a modulated square lattice and its implications for the antiferromagnetic phase of KyFeYu1, Goswami2, Si3 2011Phys. Rev. BSelf Cite311190View full textAdd to dashboardCite

“…On the other hand, the experimentally observed large electrical resistivity ("bad metal" with k F l ∼ 1), a strong suppression of Drude weight 4 , and the temperatureinduced spectral weight transfer [5][6][7] have suggested sizable strength of electronic correlations. These experimental evidences have suggested the placement of the iron pnictides in close proximity of a putative Mott transition [8][9][10] . In a metallic system close to a Mott transition, quasi-local moments are expected to arise, which for the iron pnictides are described in terms of J 1 − J 2 couplings 8,9 ; here J 1 and J 2 refer to nearest-neighbor and next-nearest-neighbor spin exchange interactions on the iron square lattice.…”

“…These experimental evidences have suggested the placement of the iron pnictides in close proximity of a putative Mott transition [8][9][10] . In a metallic system close to a Mott transition, quasi-local moments are expected to arise, which for the iron pnictides are described in terms of J 1 − J 2 couplings 8,9 ; here J 1 and J 2 refer to nearest-neighbor and next-nearest-neighbor spin exchange interactions on the iron square lattice. Hence in the strong coupling scenario, the (π, 0) collinear antiferromagnetic order in these materials can be described in terms of such a J 1 − J 2 model.…”

Relationship between Superconductivity and Antiferromagnetism in LaFe(As1−xPx)O Revealed by 31P-NMR

“…[1][2][3][4] The relationship between superconductivity and AFM fluctuations in recent-discovered iron-based superconductors has also been discussed. [5][6][7][8][9][10][11][12][13][14][15][16] Up to now, it has been reported that superconductivity appears around the AFM quantum critical point in the Ba122 system, indicative of the strong relationship between superconductivity and low-energy AFM fluctuations. 10,[12][13][14][15][16] On the other hand, superconductivity is linked not to the low-energy AFM fluctuations probed by NMR spectroscopy but to the local stripe spin correlation with Q stripe = (π, 0) (unfolded Brillouin zone) in LaFeAs(O 1−x F x ).…”

Nanoscale chemical phase separation in FeTe0.55Se0.45as seen via scanning tunneling spectroscopy

“…Although there are some similarities to cuprates -layered structure and proximity to magnetism, Fe-based superconductors are chemically much more flexible, where superconductivity can be induced by either external pressure, or isovalent substitution (chalcogen), or partial replacement for the Fe by other transition metals. Thus these materials offer a new platform to explore collective behavior in complex transition metal compounds, including the pairing mechanism for superconductivity, the relevance of electron correlations 5,6 to the functionality, and the possible relationship between quantum critical behavior and superconductivity 7 .…”