The LaAlO 3 =SrTiO 3 interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20 K rangeindicative of a single-particle mechanism. Motivated by a striking correspondence between the temperature and carrier density dependence of our magnetoresistance measurements we propose an alternative explanation. Working in the framework of semiclassical Boltzmann transport theory we demonstrate that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence. The mobile electrons at the LaAlO 3 =SrTiO 3 (LAO=STO) interface [1] display an exotic combination of superconductivity [2,3] and magnetic order [4][5][6][7]. The onset of superconductivity at sub-Kelvin temperatures appears in an interval of electron densities where the effect of Rashba spin-orbit coupling on the band structure at the Fermi level is strongest [8,9], but whether this correlation implies causation remains unclear.Transport experiments above the superconducting transition temperature have revealed a very large ("giant") drop in the sheet resistance of the LAO=STO interface upon application of a parallel magnetic field [10][11][12][13]. An explanation has been proposed [13,14] in terms of the Kondo effect: Variation of the electron density or magnetic field drives a quantum phase transition between a highresistance correlated electronic phase with screened magnetic impurities and a low-resistance phase of polarized impurity moments. The relevance of spin-orbit coupling for magnetotransport is widely appreciated [10,[14][15][16][17][18][19], but it was generally believed to be too weak an effect to provide a single-particle explanation of the giant magnetoresistance.In this work we provide experimental data (combining magnetic field, gate voltage, and temperature profiles for the resistance of the LAO=STO interface) and theoretical calculations that support an explanation fully within the single-particle context of Boltzmann transport. The key ingredients are the combination of spin-orbit coupling, band anisotropy, and finite-range electrostatic impurity scattering.The thermal insensitivity of the giant magnetoresistance [10,11], in combination with a striking correspondence that we have observed between the gate voltage and temperature dependence of the effect, are features that are difficult to reconcile with the thermally fragile Kondo interpretationbut fit naturally in the semiclassical Boltzmann description.We first present the experimental data and then turn to the theoretical de...

Abstract. The relation between redshift and the CMB temperature, T CMB (z) = T 0 (1 + z) is a key prediction of standard cosmology, but is violated in many nonstandard models. Constraining possible deviations to this law is an effective way to test the ΛCDM paradigm and search for hints of new physics. We present state-ofthe-art constraints, using both direct and indirect measurements. In particular, we point out that in models where photons can be created or destroyed, not only does the temperature-redshift relation change, but so does the distance duality relation, and these departures from the standard behaviour are related, providing us with an opportunity to improve constraints. We show that current datasets limit possible deviations of the form T CMB (z) = T 0 (1 + z) 1−β to be β = 0.004 ± 0.016 up to a redshift z ∼ 3. We also discuss how, with the next generation of space and ground-based experiments, these constraints can be improved by more than one order of magnitude.

We investigate the thickness-dependent electronic structure of ultrathin SrIrO 3 and discover a transition from a semimetallic to a correlated insulating state below 4 unit cells. Low-temperature magnetoconductance measurements show that spin fluctuations in the semimetallic state are significantly enhanced while approaching the transition point. The electronic structure is further studied by scanning tunneling spectroscopy, showing that 4 unit cells SrIrO 3 is on the verge of a gap opening. Our density functional theory calculations reproduce the critical thickness of the transition and show that the opening of a gap in ultrathin SrIrO 3 is accompanied by antiferromagnetic order.

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