Probing momentum-dependent scattering in uniaxially stressed Sr2RuO4 through the Hall effect

Funding: The authors acknowledge the financial support of the Max Planck Society. A. P. M. and C. W. H. acknowledge the financial support of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—TRR 288–422213477 (project A10). N. K. is supported by a KAKENHI Grants-in-Aids for Scientific Research (Grants No. 17H06136, No. 18K04715, and No. 21H01033), and Core-to-Core Program (No. JPJSCCA20170002) from the Japan Society for the Promotion of Science (JSPS) and by a JST-Mirai Program (Grant No. JPMJMI18A3). H. M. L. N. acknowledges support from the Alexander von Humboldt Foundation through a Research Fellowship for Postdoctoral Researchers. Research in Dresden benefits from the environment provided by the DFG Cluster of Excellence ct.qmat (EXC 2147, project ID 390858940).The largest Fermi surface sheet of the correlated metal Sr2RuO4 can be driven through a Lifshitz transition between an electronlike and an open geometry by uniaxial stress applied along the [100] lattice direction. Here, we investigate the effect of this transition on the longitudinal resistivity ρxx and the Hall coefficient RH. ρxx(T), when Sr2RuO4 is tuned to this transition, is found to have a T2logT form, as expected for a Fermi liquid tuned to a Lifshitz transition. RH is found to become more negative as the Fermi surface transitions from an electronlike to an open geometry, opposite to general expectations from this change in topology. The magnitude of the change in RH implies that scattering changes throughout the Brillouin zone, not just at the point in k space where the transition occurs. In a model of orbital-dependent scattering, the electron-electron scattering rate on sections of Fermi surface with xy orbital weight is found to decrease dramatically.Publisher PDFPeer reviewe

Relationship between transport anisotropy and nematicity in FeSe

We thank the Max Planck Society for financial support. C. W. H., A. P. M., and C. T. acknowledge support by the DFG (DE) through the Collaborative Research Centre SFB 1143 (Projects C09 and A04). C. T. acknowledges support by the DFG (DE) through the Cluster of Excellence on Complexity and Topology in Quantum Matter ct.qmat (EXC 2147). Work in Japan was supported by Grants-in-Aid for Scientific Research (KAKENHI) (No. JP19H00649 and No. JP18H05227), and Grant-in-Aid for Scientific Research on innovative areas “Quantum Liquid Crystals” (No. JP19H05824 and No. JP20H05162) from Japan Society for the Promotion of Science (JSPS).The mechanism behind the nematicity of FeSe is not known. Through elastoresitivity measurements it has been shown to be an electronic instability. However, thus far measurements have extended only to small strains, where the response is linear. Here, we apply large elastic strains to FeSe and perform two types of measurement. (1) Using applied strain to control twinning, the nematic resistive anisotropy at temperatures below the nematic transition temperature Ts is determined. (2) Resistive anisotropy is measured as nematicity is induced through applied strain at fixed temperature above Ts. In both cases, as nematicity strengthens, the resistive anisotropy peaks at about 7%, then decreases. Below ≈40  K, the nematic resistive anisotropy changes sign. We discuss possible implications of this behavior for theories of nematicity. In addition, we report the following. (1) Under experimentally accessible conditions with bulk crystals, stress, rather than strain, is the conjugate field to the nematicity of FeSe. (2) At low temperatures the twin boundary resistance is ∼10% of the sample resistance, and must be properly subtracted to extract intrinsic resistivities. (3) Biaxial in-plane compression increases both in-plane resistivity and the superconducting critical temperature Tc, consistent with a strong role of the yz orbital in the electronic correlations.Publisher PDFPeer reviewe

Topological metamagnetism : thermodynamics and dynamics of the transition in spin ice under uniaxial compression

This work was carried out within the framework of a Max-Planck independent research group on strongly correlated systems. We acknowledge financial support from the Deutsche Forschungsgemeinschaft through SFB 1143 (Project No. 247310070) and Cluster of Excellence ct.qmat (EXC 2147, Project No. 390858490), EPSRC (EP/T028637/1), ShanghaiTech University, Agencia Nacional de Promoción Científica y Tecnológica through PICT 2017-2347, and Consejo Nacional de Investigaciones Científicas y Técnicas through PIP 0446.Metamagnetic transitions are analogs of a pressure-driven gas-liquid transition in water. In insulators, they are marked by a superlinear increase in the magnetization that occurs at a field strength set by the spin exchange interactions. Here we study topological metamagnets, in which the magnetization is itself a topological quantity and for which we find a single transition line for two materials with substantially different magnetic interactions: the spin ices Dy2Ti2O7 and Ho2Ti2O7. We study single crystals under magnetic field and stress applied along the [001] direction and show that this transition, of the Kasteleyn type, has a magnetization versus field curve with upward convexity and a distinctive asymmetric peak in the susceptibility. We also show that the dynamical response of Ho2Ti2O7 is sensitive to changes in the Ho3+ environment induced by compression along [001]. Uniaxial compression may open up experimental access to equilibrium properties of spin ice at lower temperatures.Publisher PDFPeer reviewe

Deconvoluting lung evolution: from phenotypes to gene regulatory networks

Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial "respiratory pharynx” but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration. To meet the high oxygen demands of flight, bird lungs have evolved separate gas exchange and pump components to achieve unidirectional ventilation and minimize dead space. The process of "screening” (removal of oxygen from inspired air prior to entering the terminal units) reduces effective alveolar oxygen tension and potentially explains why nonathletic large mammals possess greater pulmonary diffusing capacities than required by their oxygen consumption. The "primitive” central admixture of oxygenated and deoxygenated blood in the incompletely divided reptilian heart is actually co-regulated with other autonomic cardiopulmonary responses to provide flexible control of arterial oxygen tension independent of ventilation as well as a unique mechanism for adjusting metabolic rate. Some of the most ancient oxygen-sensing molecules, i.e., hypoxia-inducible factor-1alpha and erythropoietin, are up-regulated during mammalian lung development and growth under apparently normoxic conditions, suggesting functional evolution. Normal alveolarization requires pleiotropic growth factors acting via highly conserved cell-cell signal transduction, e.g., parathyroid hormone-related protein transducing at least partly through the Wingless/int pathway. The latter regulates morphogenesis from nematode to mammal. If there is commonality among these diverse respiratory processes, it is that all levels of organization, from molecular signaling to structure to function, co-evolve progressively, and optimize an existing gas-exchange framewor

Deconvoluting lung evolution: from phenotypes to gene regulatory networks

Speakers in this symposium presented examples of respiratory regulation that broadly illustrate principles of evolution from whole organ to genes. The swim bladder and lungs of aquatic and terrestrial organisms arose independently from a common primordial “respiratory pharynx” but not from each other. Pathways of lung evolution are similar between crocodiles and birds but a low compliance of mammalian lung may have driven the development of the diaphragm to permit lung inflation during inspiration. To meet the high oxygen demands of flight, bird lungs have evolved separate gas exchange and pump components to achieve unidirectional ventilation and minimize dead space. The process of “screening” (removal of oxygen from inspired air prior to entering the terminal units) reduces effective alveolar oxygen tension and potentially explains why nonathletic large mammals possess greater pulmonary diffusing capacities than required by their oxygen consumption. The “primitive” central admixture of oxygenated and deoxygenated blood in the incompletely divided reptilian heart is actually co-regulated with other autonomic cardiopulmonary responses to provide flexible control of arterial oxygen tension independent of ventilation as well as a unique mechanism for adjusting metabolic rate. Some of the most ancient oxygen-sensing molecules, i.e., hypoxia-inducible factor-1alpha and erythropoietin, are up-regulated during mammalian lung development and growth under apparently normoxic conditions, suggesting functional evolution. Normal alveolarization requires pleiotropic growth factors acting via highly conserved cell–cell signal transduction, e.g., parathyroid hormone-related protein transducing at least partly through the Wingless/int pathway. The latter regulates morphogenesis from nematode to mammal. If there is commonality among these diverse respiratory processes, it is that all levels of organization, from molecular signaling to structure to function, co-evolve progressively, and optimize an existing gas-exchange framework

Noise Characteristics of 100nm-scaleGaAs/Al_xGa_{1-x}As Scanning Hall Probes

The authors have fabricated and characterized GaAs/Al{sub x}Ga{sub 1-x}As two-dimensional electron gas scanning Hall probes for imaging perpendicular magnetic fields at surfaces. The Hall crosses range from 85 x 85 to 1000 x 1000 nm{sup 2}. They study low-frequency noise in these probes, especially random telegraph noise, and show that low-frequency noise can be significantly reduced by optimizing the voltage on a gate over the Hall cross. The authors demonstrate a 100 nm Hall probe with a sensitivity of 0.5 G/{radical}Hz (flux sensitivity of 0.25m {Phi}{sub 0}/{radical}Hz; spin sensitivity of 1.2 x 10{sup 4} {mu}{sub B}/{radical}Hz) at 3 Hz and 9 K

Backward-angle photoproduction of π0\pi^0 mesons on the proton at EγE_\gamma = 1.5--2.4 GeV

Differential cross sections and photon beam asymmetries for $\pi^0$ photoproduction have been measured at $E_\gamma$ = 1.5--2.4 GeV and at the $\pi^0$ scattering angles, --1 $<$ cos$\Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $\pi^0$ production has been determined. An enhancement at backward angles is found above $E_\gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_\gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL

Forward coherent ϕ\phi-meson photoproduction from deuterons near threshold

Differential cross sections and decay asymmetries for coherent $\phi$-meson photoproduction from deuterons were measured for the first time at forward angles using linearly polarized photons at $E_{\gamma}$= 1.5-2.4 GeV. This reaction offers a unique way to directly access natural-parity Pomeron dynamics and gluon exchange at low energies. The cross sections at zero degrees increase with increasing photon energy. The decay asymmetries demonstrate a complete dominance of natural-parity exchange processes, showing that isovector unnatural-parity $\pi$-meson exchange is small. Nevertheless the deduced cross sections of $\phi$-mesons from nucleons contributed by isoscalar t-channel exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio

Observation of exclusive DVCS in polarized electron beam asymmetry measurements

We report the first results of the beam spin asymmetry measured in the reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry with a sin(phi) modulation is observed, as predicted for the interference term of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and leading-twist pQCD, the alpha is directly proportional to the imaginary part of the DVCS amplitude.Comment: 6 pages, 5 figure

From thermal rectifiers to thermoelectric devices

We discuss thermal rectification and thermoelectric energy conversion from the perspective of nonequilibrium statistical mechanics and dynamical systems theory. After preliminary considerations on the dynamical foundations of the phenomenological Fourier law in classical and quantum mechanics, we illustrate ways to control the phononic heat flow and design thermal diodes. Finally, we consider the coupled transport of heat and charge and discuss several general mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture Notes in Physics volume "Thermal transport in low dimensions: from statistical physics to nanoscale heat transfer" (S. Lepri ed.