Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides

Abstract

Considerations of the observed bad-metal behavior in Fe-based superconductors led to an early proposal for quantum criticality induced by isoelectronic P for As doping in iron arsenides, which has since been experimentally confirmed. We study here an effective model for the isoelectronically tuned pnictides using a large-N approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for J 1 -J 2 exchange-coupled local moments on an Fe square lattice, and a damping caused by coupling to itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the interplane coupling; consequently, quantum criticality occurs over a wide dynamical range. Our results reconcile recent seemingly contradictory experimental observations concerning the quantum phase transition in the P-doped iron arsenides.

ω/T scaling and magnetic quantum criticality in BaFe2(As0.7P0.3)2

“…Consequently, it drives both the AF and nematic quantum phase transitions to be concurrent and weakly first order, resulting in a large dynamical range of quantum criticality [21]. The same conclusion follows from a large-N saddle-point calculation [50].…”

“…Quantum criticality associated with a weakly firstorder but concurrent AF and nematic quantum phase transitions were anticipated theoretically for the Psubstituted iron arsenides [21,50]. P-for-As substitution effectively decreases the strength of electron correlations by enhancing the kinetic energy, thereby reducing the magnetic and the concomitant nematic order.…”

Nematic and Antiferromagnetic Quantum Criticality in a Multi-Orbital Hubbard Model for Iron Pnictides

“…However, because the coupling is only marginally relevant, it is a weakly first order transition: The jump of the order parameter is very small compared to the saturated moment, leaving an extended dynamical range for quantum criticality [21]. The same conclusion is derived by a saddle-point calculation in a large-N limit of the field theory [22], and is consistent with experimental observations [14,17,18,42]. In our microscopic study, the numerical results point to a unique QCP for the transition of both orders; however, our data do not rule out the quantum phase transition to be weakly first order, with the order parameters experiencing a small jump.…”

“…From the theoretical perspective, quantum criticality in iron pnictides was proposed within an effective field theory that contains both AFM and nematic order parameters [21,22]. This theoretical analysis provided the basis for the early proposal of realizing quantum criticality in P-doped iron arsenides [21].…”

Unconventional Antiferromagnetic Quantum Critical Point in Ba(Fe0.97Cr0.03)2(As1−xZhang1, Yuan2, Xie3 et al. 2019Phys. Rev. Lett.92100View full textAdd to dashboardCite

“…Both the AFM and nematic QCPs are suggested to present around the optimal doping level [4,16]. Even when the AFM order disappears in a weakly first-order fashion [17,18], magnetic quantum critical fluctuations may still present [19]. While the superconductivity may be completely suppressed by the magnetic field [14,15], the limited probes make it hard to further understand the nature of the QCP.…”