Unified Phase Diagram for Iron-Based Superconductors

Abstract

High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.

Unconventional Antiferromagnetic Quantum Critical Point in Ba(Fe0.97Cr0.03)2(As1−xZhang1, Yuan2, Xie3 et al. 2019Phys. Rev. Lett.Self Cite82100View full textAdd to dashboardCite

“…The values of A show little change with doping and are about 0.002 K=MPa from x ¼ 0.31 to 0.41. Compared to that in optimally doped BFAP [22], A in Cr-BFAP is much smaller, suggesting strong suppression of nematic fluctuations. More importantly, the low-temperature upturn of ζ immediately disappears when x is larger than 0.42 and ζ becomes negative at low temperature.…”

“…However, this effect will not remove the divergent behavior of nematic susceptibility when approaching to the nematic transition, as demonstrated by the upturns at low temperature for x < 0.42. These upturns can be roughly fitted by a Curie-Weiss-like function, ζ ¼ A=ðT − T 0 Þ þ y 0 , as done in other systems [5,22]. The values of A show little change with doping and are about 0.002 K=MPa from x ¼ 0.31 to 0.41.…”

“…The resistance and heat capacity were measured on the physical property measurement system (PPMS, Quantum Design). The nematic susceptibility is also measured on the PPMS with a homemade uniaxial pressure device based on a piezobender [5,22]. The magnetoresistance was measured at Wuhan National High Magnetic Field Center, China.…”

“…To see whether there is also a nematic QCP, we studied the nematic susceptibility by measuring the elastoresistivity under uniaxial pressure along the tetragonal [110] direction [5,22]. As reported previously, we define ζ as dðΔR=R 0 Þ=dp, where R 0 is the resistance at zero pressure and ΔR ¼ RðpÞ − Rð0Þ [5].…”

Revealing fermionic quantum criticality from new Monte Carlo techniques

“…In the studies of nFLs, one of the central focuses is systems with itinerant quantum critical points (IQCPs), which have attracted extensive research efforts for nearly half century dating back to the celebrated Hertz-Millis-Moriya (HMM) framework [4][5][6]. In the study of correlated quantum materials, quantum criticality in itinerant electron systems is of great importance and interests [1,[3][4][5][6][7][8][9], and it plays an important role in the understanding of anomalous transport, strange metal and nFL behaviors [10][11][12][13][14] in various quantum materials, such as heavy-fermion materials [2,15], Cu-and Fe-based hightemperature superconductors [16][17][18][19], the recently discovered pressure-driven quantum critical point (QCP) between magnetic order and superconductivity in transition-metal monopnictides, CrAs [20], MnP [21], CrAs 1−x P x [22] and other Cr/Mn-3d electron systems [23] and the more recent discoveries in twisted angle graphene heterostructures [24][25][26]. However, after decades of extensive efforts [1,[3][4][5][6][7][8][9][10][27][28][29]…”