Unconventional localization of electrons inside of a nematic electronic phase

Abstract

The magnetotransport behavior inside the nematic phase of bulk FeSe reveals unusual multiband effects that cannot be reconciled with a simple two-band approximation proposed by surface-sensitive spectroscopic probes. In order to understand the role played by the multiband electronic structure and the degree of two-dimensionality, we have investigated the electronic properties of exfoliated flakes of FeSe by reducing their thickness. Based on magnetotransport and Hall resistivity measurements, we assess the mobility spectrum that suggests an unusual asymmetry between the mobilities of the electrons and holes, with the electron carriers becoming localized inside the nematic phase. Quantum oscillations in magnetic fields up to 38 T indicate the presence of a hole-like quasiparticle with a lighter effective mass and a quantum scattering time three times shorter, as compared with bulk FeSe. The observed localization of negative charge carriers by reducing dimensionality can be driven by orbitally dependent correlation effects, enhanced interband spin fluctuations, or a Lifshitz-like transition, which affect mainly the electron bands. The electronic localization leads to a fragile two-dimensional superconductivity in thin flakes of FeSe, in contrast to the two-dimensional high- T c induced with electron doping via dosing or using a suitable interface.

Drastic effect of impurity scattering on the electronic and superconducting properties of Cu-doped FeSe

“…3(c), which would be consistent with the existence of strong antiferromagnetic critical fluctuations in the presence of disorder [41]. Similar findings were also detected in thin flakes in the presence of strong two-dimensional fluctuations and disorder [37].…”

“…Interestingly, in FeSe samples with larger amounts of disorder (smaller RRR values), the resistivity seems to display linear behavior at lowest temperatures. This behavior was also found in FeSe crystals with small RRR values [10,38], Cusubstituted FeSe, and thin flakes of FeSe [37]. In the vicinity of an itinerant antiferromagnetic quantum critical point, as proposed for FeSe [57], the resistivity is strongly affected by small amounts of disorder.…”

“…We find that the mobilities of all charge carriers are significantly reduced, as compared with FeSe, by roughly a factor of 3, due to the increase in the scattering rate μ = eτ /m * , as Cu ions act as strong scattering centers [34]. An unusual disparity occurs between the hole and electron behaviors at low temperatures, with electron mobilities becoming rather less temperature dependent below 50 K, similar to thin flake devices [37]. At low temperatures, the impurity scattering dominates the changes in spectrum, as seen in the increased values of ρ 0 , and similar reductions were seen at higher Cu doping at 10 K [16].…”

Review of Single Crystal Synthesis of 11 Iron-Based Superconductors

“…However, a breakthrough was achieved through the preparation of high-quality FeSe single crystals using the CVT method with a KCl/AlCl 3 transport agent [13,68]. A distinct kink at approximately 90 K was observed in the temperature dependence of resistance R(T) and was confirmed to be a structural(nematic) transition from the tetragonal to orthorhombic phase [12,[68][69][70][71][72]. The temperature dependence of resistance and magnetic susceptibility confirmed the presence of a superconducting transition around 9.4 K. The superconducting transition width of about 1.5 K and a nearly 100% superconducting volume fraction demonstrated good superconductivity [68].…”