In cuprate high-temperature superconductors the doping level is fixed during synthesis, hence the charge carrier density per CuO_2 plane cannot be easily tuned by conventional gating, unlike in 2D materials. Strain engineering has recently emerged as a powerful tuning knob for manipulating the properties of cuprates, in particular charge and spin orders, and their delicate interplay with superconductivity. In thin films, additional tunability can be introduced by the substrate surface morphology, particularly nanofacets formed by substrate surface reconstruction. Here we show a remarkable enhancement of the superconducting onset temperature T_c^on and the upper critical magnetic field H_c,2 in nanometer-thin YBa_2Cu_3O_7-δ films grown on a substrate with a nanofaceted surface. We theoretically show that the enhancement is driven by electronic nematicity and unidirectional charge density waves, where both elements are captured by an additional effective potential at the interface between the film and the uniquely textured substrate. Our findings show a new paradigm in which substrate engineering can effectively enhance the superconducting properties of cuprates. This approach opens an exciting frontier in the design and optimization of high-performance superconducting materials.

It has recently become clear that phonons generate a sizable thermal Hall effect in cuprates, whether they are undoped, electron-doped or hole-doped (inside the pseudogap phase). At higher doping, where cuprates are reasonably good metals, mobile electrons also generate a thermal Hall effect, the thermal equivalent of the standard electrical Hall effect. Here we show that in the cleanest crystals of the electron-doped cuprate Nd$_{2-x}$Ce$_{x}$CuO$_{4}$, at high doping, the phonon and electron contributions to the thermal Hall conductivity $\kappa_{\rm {xy}}$ are of comparable magnitude, but of opposite sign. In samples of lower quality, phonons dominate $\kappa_{\rm {xy}}$, resulting in a negative $\kappa_{\rm {xy}}$ at all temperatures. The fact that the negative phononic $\kappa_{\rm {xy}}$ in the metallic state is similar in magnitude and temperature dependence to that found in the insulating state at lower doping rules out any mechanism based on skew scattering of phonons off charged impurities, since a local charge should be screened in the metallic regime. The phononic $\kappa_{\rm {xy}}$ is found to persist over the entire doping range where antiferromagnetic correlations are known to be significant, suggesting that such correlations may play a role in generating the phonon thermal Hall effect in electron-doped cuprates. If the same mechanism is also at play in hole-doped cuprates, the presence of a phononic $\kappa_{\rm {xy}}$ below (and only below) the critical doping $p^{\star}$ would be evidence that spin correlations are a property of the pseudogap phase.

High magnetic fields have proven instrumental in exploring the physical properties of condensed matter, leading to groundbreaking discoveries such as the quantum Hall effect in 2D heterostructures and quantum oscillations in cuprate superconductors. The ability to conduct precise measurements at progressively higher magnetic fields continues to push the frontiers of knowledge and enable new discoveries. In this work, we present the development of a microwave technique for performing two-point transport measurements in semi-destructive pulsed magnetic fields (up to 125 T) and at low temperatures (down to 1.5 K) with unprecedented sensitivity. This new setup was tested on a variety of samples. We present results on the metal-insulator transition in InAs and we report notably the first observation of Shubnikov-de-Haas oscillations in WTe_2 at magnetic fields beyond 100 T.

We study the transport properties of underdoped trilayer cuprate HgBa$_2$Ca$_2$Cu$_3$O$_{8+ \delta}$ with doping level $p$ = 0.1 - 0.12 in magnetic field up to 88 T. We report for the first time in a cuprate superconductor a dramatic change of the quantum oscillation spectrum versus temperature, which is accompanied by a sign change of the Hall effect below $T \approx$ 10 K. Based on numerical simulations, we infer a Fermi surface reconstruction in the inner plane from an antiferromagnetic state (hole pockets) to a biaxial charge density wave state (electron pockets). We show that both orders compete and share the same hotspots of the Fermi surface and we discuss our result in the context of spin-fermion models.

Abstract The signature feature of the ‘strange metal’ state of high-T c cuprates—its linear-in-temperature resistivity—has a coefficient α 1 that correlates with T c , as expected were α 1 derived from scattering off the same bosonic fluctuations that mediate pairing. Recently, an anomalous linear-in-field magnetoresistance (=γ 1 H) has also been observed, but only over a narrow doping range, leaving its relation to the strange metal state and to the superconductivity unclear. Here, we report in-plane magnetoresistance measurements on three hole-doped cuprate families spanning a wide range of temperatures, magnetic field strengths and doping. In contrast to expectations from Boltzmann transport theory, γ 1 is found to correlate universally with α 1. A phenomenological model incorporating real-space inhomogeneity is proposed to explain this correlation. Within this picture, superconductivity in hole-doped cuprates is governed not by the strength of quasiparticle interactions with a bosonic bath, but by the concentration of strange metallic carriers.

Strange metals challenge our understanding of charge transport in metals. Here, we investigate how the strange metal phase of La_2-xSr_xCuO_4 is impacted by a field-induced glassy antiferromagnetic state. Using magnetic fields above 80 T, we discover a strong enhancement of the normal state magnetoresistance when entering the spin glass phase. We demonstrate that the spin glass causes insulating-like upturns in the resistivity inside the pseudogap phase, which resolves the origin of the ”metal-insulator” crossover. In addition the strange metal phase appears at low temperatures over an extended range of magnetic fields where magnetic moments fluctuate, and disappears when these moments freeze out. We conclude that the transport properties of the strange metal phase are controlled by magnetic fluctuations persisting at the lowest temperatures.

The recently discovered layered kagome metals of composition AV_{3}Sb_{5} (A=K, Rb, Cs) exhibit a complex interplay among superconductivity, charge density wave order, topologically nontrivial electronic band structure and geometrical frustration. Here, we probe the electronic band structure underlying these exotic correlated electronic states in CsV_{3}Sb_{5} with quantum oscillation measurements in pulsed fields up to 86 T. The high-field data reveal a sequence of magnetic breakdown orbits that allows the construction of a model for the folded Fermi surface of CsV_{3}Sb_{5}. The dominant features are large triangular Fermi surface sheets that cover almost half the folded Brillouin zone. These sheets have not yet been detected in angle resolved photoemission spectroscopy and display pronounced nesting. The Berry phases of the electron orbits have been deduced from Landau level fan diagrams near the quantum limit without the need for extrapolations, thereby unambiguously establishing the nontrivial topological character of several electron bands in this kagome lattice superconductor.

High Field Magnet Laboratory (HFML-EMFL) and Institute for Molecules and Materials, Radboud University, Toernooiveld 7, 6525 ED Nijmegen, Netherlands H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, United Kingdom LNCMI-EMFL, CNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, INSA-T, Grenoble and Toulouse, France Van der Waals-Zeeman Institute, University of Amsterdam, Postbus 94485, 1090 GL Amsterdam, Netherlands Institute for Solid State Physics, University of Tokyo, Kashiwa-no-ha, Kashiwa, Japan Toyota Technological Institute, Nagoya 468-8511, Japan Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, United Kingdom

The ultra-quantum limit is achieved when a magnetic field confines an electron gas in its lowest spin-polarised Landau level. Here we show that in this limit, electron doped ZrTe5 shows a metal-insulator transition followed by a sign change of the Hall and Seebeck effects at low temperature. We attribute this transition to a magnetic freeze-out of charge carriers on the ionized impurities. The reduction of the charge carrier density gives way to an anomalous Hall response of the spin-polarised electrons. This behavior, at odds with the usual magnetic freeze-out scenario, occurs in this Dirac metal because of its tiny Fermi energy, extremely narrow band gap and a large g-factor. We discuss the different possible sources (intrinsic or extrinsic) for this anomalous Hall contribution.

In various so-called strange metals, electrons undergo Planckian dissipation 1 , 2 , a strong and anomalous scattering that grows linearly with temperature 3 , in contrast to the quadratic temperature dependence expected from the standard theory of metals. In some cuprates 4 , 5 and pnictides 6 , a linear dependence of resistivity on a magnetic field has also been considered anomalous—possibly an additional facet of Planckian dissipation. Here we show that the resistivity of the cuprate strange metals Nd 0.4 La 1.6− x Sr x CuO 4 (ref. 7 ) and La 2− x Sr x CuO 4 (ref. 8 ) is quantitatively consistent with the standard Boltzmann theory of electron motion in a magnetic field, in all aspects—field strength, field direction, temperature and disorder level. The linear field dependence is found to be simply the consequence of scattering rate anisotropy. We conclude that Planckian dissipation is anomalous in its temperature dependence, but not in its field dependence. The scattering rate in these cuprates does not depend on field, which means that their Planckian dissipation is robust against fields up to at least 85 T.

Multilayered cuprates possess not only the highest superconducting temperature transition but also offer a unique platform to study disorder-free CuO2 planes and the interplay between competing orders with superconductivity. Here, we study the underdoped trilayer cuprate HgBa2Ca2Cu3O8+δ and we report quantum oscillation and Hall effect measurements in magnetic field up to 88 T. A careful analysis of the complex spectra of quantum oscillations strongly supports the coexistence of an antiferromagnetic order in the inner plane and a charge order in the outer planes. The presence of an ordered antiferromagnetic metallic state that extends deep in the superconducting phase is a key ingredient that supports magnetically mediated pairing interaction in cuprates.

It has long been recognized that the key to unlocking the mystery of cuprate high-Tc superconductivity lies in understanding the anomalous normal state from which pairs form and condense. While many of its defining properties have been identified, they are often considered either at a singular doping level or as an isolated phenomenon as a function of doping. As a result, their relation to each other and to the pseudogap (PG), strange metal (SM) and non-superconducting (non-SC) regimes that define the cuprate phase diagram has yet to be elucidated. Here, we report a high-field in-plane MR study on several cuprate families spanning all 3 regimes that reveal a complex yet nonetheless systematic evolution of the form of the MR, with each regime possessing its own distinct scaling behavior. In the PG regime, the MR exhibits pure H/T^2 scaling at low fields and H-linearity at the highest field strengths. While the H-linearity persists inside the SM regime, the scaling changes abruptly to H/T. The size of the H-linear slope, meanwhile, is found to be correlated with both the T-linear resistivity coefficient and Tc, strengthening the characterization of the SM regime as a quantum critical phase. We interpret the omnipresence of H-linear MR across both regimes as a signature of highly anisotropic, possibly discontinuous features on the Fermi surface. Finally, within the non-SC, Fermi-liquid regime, we observe a recovery of conventional Kohler scaling. This comprehensive study establishes the distinct nature of the magnetotransport within each regime and identifies power-law scaling of the normal state MR as a defining feature of SC hole-doped cuprates. The incompatibility of such power-law scaling with any known variant of Boltzmann transport theory motivates the quest for an altogether new theoretical framework, one in which the MR is entirely decoupled from elastic impurity scattering.

HgBa2Ca2Cu3O8+δ V. Oliviero1,†, S. Benhabib1,†,‡,∗, I. Gilmutdinov, B. Vignolle, L. Drigo , M. Massoudzadegan, M. Leroux, G.L.J.A. Rikken, A. Forget, D. Colson, D. Vignolles1,∗ and C. Proust1,∗ LNCMI-EMFL, CNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, INSA-T, Grenoble and Toulouse, France Institut de Chimie de la Matière Condensée, Bordeaux, France Service de Physique de l’Etat Condensé, CEA Saclay (CNRS-URA 2464), Gif sur Yvette 91191, France

Electronic topology in metallic kagome compounds is under intense scrutiny. We present transport experiments in Na2/3CoO2 in which the Na order differentiates a Co kagome sub-lattice in the triangular CoO2 layers. Hall and magnetoresistance (MR) data under high fields give evidence for the coexistence of light and heavy carriers. At low Ts, the dominant light carrier conductivity at zero field is suppressed by a B-linear MR suggesting Dirac like quasiparticles. Lifshitz transitions induced at large B and T unveil the lower mobility carriers. They display a negative B^2 MR due to scattering from magnetic moments likely pertaining to a flat band. We underline an analogy with heavy Fermion physics.

Quantum materials harbor a cornucopia of exotic transport phenomena challenging our understanding of condensed matter. Among these, a giant, nonsaturating linear magnetoresistance (MR) has been reported in various systems, from Weyl semimetals to topological insulators. Its origin is often ascribed to unusual band structure effects, but it may also be caused by extrinsic sample disorder. Here, we report a very large linear MR in a SrTiO3 two-dimensional electron gas and, by combining transport measurements with electron spectromicroscopy, show that it is caused by nanoscale inhomogeneities that are self-organized during sample growth. Our data also reveal semiclassical Sondheimer oscillations arising from interferences between helicoidal electron trajectories, from which we determine the 2DEG thickness. Our results bring insight into the origin of linear MR in quantum materials, expand the range of functionalities of oxide 2DEGs, and suggest exciting routes to explore the interaction of linear MR with features like Rashba spin-orbit coupling.

Electronic topology in metallic kagome compounds is under intense scrutiny. We present transport experiments in Na2/3CoO2 in which the Na order differentiates a Co kagome sub-lattice in the triangular CoO2 layers. Hall and magnetoresistance (MR) data under high fields give evidence for the coexistence of light and heavy carriers. At low temperatures, the dominant light carrier conductivity at zero field is suppressed by a B-linear MR suggesting Dirac like quasiparticles. Lifshitz transitions induced at large B and T unveil the lower mobility carriers. They display a negative B^2 MR due to scattering from magnetic moments likely pertaining to a flat band. We underline an analogy with heavy Fermion physics.

A. I. Coldea, A. Carrington, R. Coldea, L. Malone, A.F. Bangura, M. D. Johannes , I. I. Mazin, E.A. Yelland, J. G. Analytis, J.A.A.J. Perenboom , C. Jaudet , D. Vignolles, T. Sorgel , M. Jansen H. H. Wills Physics Laboratory, Bristol University, Tyndall Avenue, BS8 1TL, United Kingdom Code 6393, Naval Research Laboratory, Washington, D.C. 20375, USA Max-Planck-Institut fur Festkorperforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany High Field Magnet Laboratory, IMM, Radboud University, 6525 ED Nijmegen, The Netherlands and Laboratoire National des Champs Magnetiques Pulses, 31400 Toulouse, France (Dated: June 15, 2021)

Les jeux d’evasion (escape games) connaissent un succes important depuisquelques annees. Le monde de l’education s’est tres vite interesse a ce dispositifafin de l’utiliser comme support pour la pedagogie. A l’INSA Toulouse, uneequipe enseignante a concu une activite pedagogique autour de ce dispositif :des etudiants de L2 et L3 vont realiser des enigmes basees sur les competencesqu’ils ont acquises en L1. Leurs realisations seront ensuite deployees dans uneveritable salle de jeu d’evasion pour servir de vitrine a l’INSA Toulouse. Lesetudiants du projet sont ainsi confrontes aux methodes de generation d’idees,de prototypage rapide dans un Fablab, de recontextualisation de leurs com-petences et de travail en equipe. L’article decrit les objectifs pedagogiques del’activite, sa mise en œuvre et les premiers retours d’experience.