Disentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system

Abstract

Quantum interference between time-reversed electron paths in two dimensions leads to the wellknown weak localization correction to resistance. If spin-orbit coupling is present, the resistance correction is negative, termed weak anti-localization (WAL). Here we report the observation of WAL coexisting with exchange coupling between itinerant electrons and localized magnetic moments. We use low-temperature magneto-transport measurements to investigate the quasi-two-dimensional, high-electron-density interface formed between SrTiO3 (STO) and the anti-ferromagnetic Mott insulator NdTiO3 (NTO). As the magnetic field angle is gradually tilted away from the sample normal, the data reveals the interplay between strong k-cubic Rashba-type spin-orbit coupling and a substantial magnetic exchange interaction from local magnetic regions. The resulting quantum corrections to the conduction are in excellent agreement with existing models and allow sensitive determination of the small magnetic moments (22 µB on average), their magnetic anisotropy and mutual coupling strength. This effect is expected to arise in other 2D magnetic materials systems.

From weak antilocalization to Kondo scattering in a magnetic complex oxide interface

“…Previous work has focused on the case of thin NTO layers, where these effects give rise to a unique type of WAL correction to the conductance under the combined effect of the magnetic exchange and an applied magnetic field [8]. Here we report on a striking transition between this regime, where localization effects dominate the magnetotransport response, to a regime of predominant Kondo scattering, as the thickness of the NTO layer is increased.…”

“…Conducting interfaces between SrTiO 3 (STO) and other complex oxides are an ideal system for investigating twodimensional electron systems in the high-density regime [1][2][3][4]. Our experimental system consists of epitaxial layers of SrTiO 3 and NdTiO 3 (NTO) [4][5][6], which host a highdensity quasi-two-dimensional electron gas coupled to local ferromagnetic or superparamagnetic regions [7,8]. The ferromagnetic order is thought to originate from spatially inhomogeneous canting of the antiferromagnetically-alligned spins in NTO [7,9], which is a Mott-Hubbard insulator with a Néel temperature of ∼ 90 K [10,11].…”

“…The top STO layer protects the underlying heterostructure from degradation [6], however only the bottom NTO-on-STO interface is expected to contribute to transport, as STO-on-NTO interfaces are typically insulating [5,7]. In this system, itinerant electrons, which reside primarily on the STO side of the interface [5], experience the combined effect of k-cubic Rashba spin-orbit coupling and a magnetic exchange interaction of several 10's of Tesla due to the local, inhomogeneous magnetic order [8].…”

“…1(c) shows the sample magnetoresistance (MR) as a function of perpendicular field B ⊥ measured at T = 2 K. The data for the 2 u.c. sample has the characteristic shape of WAL, with sharp positive MR clearly seen around zero field, and a maximum value at at larger field, around B ⊥ = 2 T. The WAL/WL contribution to the magetoresistance in B ⊥ can be analyzed to extract the dephasing and SOC parameters of the system, B φ and B so [8]. The focus of this work is on the dependence of the MR on the NTO thickness.…”

Two-fold symmetric superconductivity in few-layer NbSe2

“…In contrast, when the magnetic field is directed along  = 135°, the conductance does not change appreciably compared to that of 0 T, indicating a higher resilience of the superconducting state to magnetic fields at this angle, and highlighting the twofold anisotropy of this state. Note that due to the ferromagnetism of CrBr 3 , we expect magnetic proximity to be present at the CrBr 3 /NbSe 2 interface 36 , enhancing the effect of the applied magnetic field. In previous studies by some of us 34 , we have investigated over ten bilayer and trilayer NbSe 2 tunnel junctions with nonmagnetic insulating barriers and electrodes under an arbitrary in-plane magnetic field direction relative to the NbSe 2 edge and have observed a monotonically decreasing gap from zero field up to the upper critical field (~38T).…”