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Many envisioned applications of semiconductor nanocrystals (NCs), such as thermoelectric generators and transparent conductors, require metallic (nonactivated) charge transport across an NC network. Although encouraging signs of metallic or near-metallic transport have been reported, a thorough demonstration of nonzero conductivity, σ, in the 0 K limit has been elusive. Here, we examine the temperature dependence of σ of ZnO NC networks. Attaining both higher σ and lower temperature than in previous studies of ZnO NCs (T as low as 50 mK), we observe a clear transition from the variable-range hopping regime to the metallic regime. The critical point of the transition is distinctly marked by an unusual power law close to σ ∝ T1/5. We analyze the critical conductivity data within a quantum critical scaling framework and estimate the metal-insulator transition (MIT) criterion in terms of the free electron density, n, and interparticle contact radius, ρ.

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.

Complex oxide interfaces are a promising platform for studying a wide array of correlated electron phenomena in low-dimensions, including magnetism and superconductivity. The microscopic origin of these phenomena in complex oxide interfaces remains an open question. Here we investigate for the first time the magnetic properties of semi-insulating NdTiO 3 /SrTiO 3 (NTO/STO) interfaces and present the first milli-Kelvin study of NTO/STO. The magnetoresistance (MR) reveals signatures of local ferromagnetic order and of spin-dependent thermally-activated transport, which are described quantitatively by a simple phenomenological model. We discuss possible origins of the interfacial ferromagnetism. In addition, the MR also shows transient hysteretic features on a timescale of ~10-100 seconds. We demonstrate that these are consistent with an extrinsic magneto-thermal origin, which may have been misinterpreted in previous reports of magnetism in STO-based oxide interfaces. The existence of these two MR regimes (steady-state and transient) highlights the importance of timedependent measurements for distinguishing signatures of ferromagnetism from other effects that can produce hysteresis at low temperatures.The interface between two complex oxides can host a high-mobility conducting electron gas, even though the constituent materials are insulators. Since the initial discovery of this phenomenon in LaAlO 3 /SrTiO 3 (LAO/STO) heterostructures [1], several other materials systems with this property have been identified [2][3][4]. These systems host a range of highly-correlated phases, including superconductivity [5,6] and ferromagnetism [7][8][9][10][11][12]. While superconductivity has been conclusively detected using transport [5,6,8,13] and scanning-probe measurements [9], reports of magnetism have been more difficult to reconcile across experiments. Numerous studies have investigated the magnetic properties of this class of oxide interfaces, with the majority of work to date focusing on the canonical LAO/STO system [7][8][9][10]14]. However, a unified picture of ferromagnetism is still lacking [7][8][9][15][16][17][18].Magneto-transport studies [7,10,19], have reported pronounced magnetic hysteresis, suggestive of

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