Magnetotransport study of the pressure-induced antiferromagnetic phase in FeSe

Abstract

The resistivity ρ and Hall resistivity ρH are measured on FeSe at pressures up to P = 28.3 kbar in magnetic fields up to B = 14.5 T. The ρ(B) and ρH (B) curves are analyzed with multicarrier models to estimate the carrier density and mobility as a function of P and temperature (T 110 K). It is shown that the pressure-induced antiferromagnetic transition is accompanied by an abrupt reduction of the carrier density and scattering. This indicates that the electronic structure is reconstructed significantly by the antiferromagnetic order.PACS numbers: 74.70. Xa, 72.15.Gd, 74.25.Dw, 74.25.Jb Since the discovery of superconductivity (SC) at T c = 26 K in LaFeAs(O 1−x F x ) by Kamihara et al.[1], the iron-based high-T c materials have intensively been studied. Yet, the paring mechanism is still highly controversial: some propose spin fluctuations as the glue [2, 3], while others orbital ones [4, 5]. Intimately related to this issue is the origin of the nematic transition [6]. Typical iron-pnictide parent compounds such as LaFeAsO or BaFe 2 As 2 [7,8] exhibit a tetragonal-toorthorhombic structural transition at T s , slightly above or at the same temperature as a stripe-type antiferromagnetic (AFM) order at T N . Electronic properties below T s exhibit in-plane anisotropy that is much stronger than expected from the slight orthorhombic distortion [9][10][11][12]. It is therefore believed that the structural transition is driven by electronic (i.e., spin or orbital) degrees of freedom and thus it is called a nematic transition. T s and T N are reduced simultaneously by pressure or chemical substitution, resulting in a phase diagram where the AFM phase is enclosed by the nematic one [9]. This is consistent with scenarios of spin-driven nematicity [6,13]. An SC dome appears around points where T s and T N reach zero.) initially attracted attention because of a remarkable enhancement of T c by pressure [15][16][17][18]. A report of T c > 50 K in single-layer films [19] has also aroused considerable interest. At the same time, FeSe may be crucial in determining the paring glue and the origin of the nematicity in the iron-based superconductors. It undergoes a structural transition at T s ∼ 90 K but does not order magnetically at ambient pressure [20]. A large splitting of the d xz and d yz bands below ∼ T s found by angle-resolved photoemission spectroscopy indicates that the transition at T s is a nematic one accompanied by orbital polarization [21][22][23]. An AFM transition can be induced by pressure [24][25][26]. However, the phase diagram (see Fig. 1 and [26][27][28]) is distinct from the typical one described above for the iron-pnictide compounds. This casts some doubts on the spin-nematic scenarios. It is however to be noted that low-energy AFM spin fluctuations have been observed below T s in NMR and inelastic neutron scattering measurements [29][30][31][32][33][34]. In addition, very recent reports suggest that at high pressures (P 18 kbar, Fig. 1) where no separate structural transition at T s is seen the AFM tr...

Enhanced superconductivity induced by several-unit-cells diffusion in an FeTe/FeSe bilayer heterostructure

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On the Remarkable Superconductivity of FeSe and Its Close Cousins

“…Indirect measurements of the electronic structure as a function of temperature are magnetotransport investigations where a sharp increase of the resistance below T s [87,88] was found. This was subsequently interpreted as changes in the carrier density and the mobility in the orthorhombic phase [87,[89][90][91][92][93] which in this view point towards drastic changes of the low energy properties and the Fermi surface.…”

Emergent high-spin state above 7 GPa in superconducting FeSe

“…The superconducting critical temperature in FeSe shows drastic changes with pressure. After an initial increase, T c dips at the onset of AFM order, which is attributed to a reduction in the density of states due to a reconstruction of the Fermi surface [16,17]. Increasing the pressure further enhances both the magnetic and superconducting orders, with T N reaching a maximum of 45-55 K [8,10] at ∼ 4.2 GPa and T c plateauing around 20 K below this pressure [10,18].…”