Anomalous magnetoresistance due to longitudinal spin fluctuations in a Jeff = 1/2 Mott semiconductor

Abstract

As a hallmark of electronic correlation, spin-charge interplay underlies many emergent phenomena in doped Mott insulators, such as high-temperature superconductivity, whereas the half-filled parent state is usually electronically frozen with an antiferromagnetic order that resists external control. We report on the observation of a positive magnetoresistance that probes the staggered susceptibility of a pseudospin-half square-lattice Mott insulator built as an artificial SrIrO3/SrTiO3 superlattice. Its size is particularly large in the high-temperature insulating paramagnetic phase near the Néel transition. This magnetoresistance originates from a collective charge response to the large longitudinal spin fluctuations under a linear coupling between the external magnetic field and the staggered magnetization enabled by strong spin-orbit interaction. Our results demonstrate a magnetic control of the binding energy of the fluctuating particle-hole pairs in the Slater-Mott crossover regime analogous to the Bardeen-Cooper-Schrieffer-to-Bose-Einstein condensation crossover of ultracold-superfluids.

Manipulation of the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron‐Filling

“…Although the AFM insulating ground state can be captured by a Hubbard model similar to the AFM Mott insulator La 2 CuO 4 , its smaller U/t-value for J eff = 1/2 electrons leads to a much smaller Mott gap, allowing significant charge fluctuations and hence longitudinal spin fluctuations. [39] The previous studies reveal that external magnetic field can be employed to suppress such spin-charge fluctuations due to the hidden SU (2) symmetry of the J eff = 1/2 square lattice with octahedral rotation, giving rise to an anomalous positive magnetoresistance (MR) that is maximized around T N . [39] Indeed, the pristine SL shows the largest in-plane MR at 9 T around 135 K, as shown in Figure 3d and Figure S2b, Supporting Information, and this anomalous temperature-dependence mimics the longitudinal spin susceptibility and affords a convenient route to monitor the AFM transition and the spin fluctuations.…”

“…[39] The previous studies reveal that external magnetic field can be employed to suppress such spin-charge fluctuations due to the hidden SU (2) symmetry of the J eff = 1/2 square lattice with octahedral rotation, giving rise to an anomalous positive magnetoresistance (MR) that is maximized around T N . [39] Indeed, the pristine SL shows the largest in-plane MR at 9 T around 135 K, as shown in Figure 3d and Figure S2b, Supporting Information, and this anomalous temperature-dependence mimics the longitudinal spin susceptibility and affords a convenient route to monitor the AFM transition and the spin fluctuations. During the ILG, with increasing V G above threshold voltage, the peak of MR shifts systematically toward lower temperatures, implying that the AFM order is gradually suppressed along protonation.…”

“…Although the AFM insulating ground state can be captured by a Hubbard model similar to the AFM Mott insulator La2CuO4, its smaller U/t-value for Jeff = 1/2 electrons leads to a much smaller Mott gap, allowing significant charge fluctuations and hence longitudinal spin fluctuations [39] . The previous studies reveal that external magnetic field can be employed to suppress such spin-charge fluctuations due to the hidden SU (2) symmetry of the Jeff = 1/2 square lattice with octahedral rotation, giving rise to an anomalous positive magnetoresistance (MR) that is maximized around TN [39] .…”

Sign reversal of anomalous Hall conductivity and magnetoresistance in cubic non-collinear antiferromagnet Mn$_3$Pt thin films

“…In the high temperature NCAFM phase, the spins in the three sublattices point at an angle of 120 o relative to each other that are restricted within the kagome plane. Upon application of magnetic field, fluctuations in one of the sublattices, preferably the one with spins parallel to the field direction, may decrease while the other two may experience an increase in fluctuations leading to positive MR [38][39][40]. On the contrary, in a low temperature weak ferromagnetic phase caused by spin-reorientation or canting of Mn moments out-of-thekagome plane, external fluctuations can be suppressed by the magnetic field giving rise to negative MR [38].…”

Exciton condensation in bilayer spin-orbit insulator

“…The discovery of low-dimensional intermediate-coupling 4d and 5d-electron correlated insulators introduces a knob, U/t, that can be used to unleash the charge degrees of freedom via pressure or strain. For instance, the iridate materials [17][18][19][20][21][22] have a charge gap ∆ that is comparable to the magnon bandwidth W . The reduction of U/t leads to the suppression of the AFM ordering in favor of a paramagnetic state.…”