Nernst effect in the electron-doped cuprates

We calculate the normal state Nernst signal in the cuprates resulting from a reconstruction of the Fermi surface due to spin density wave order. An order parameter consistent with the reconstruction of the Fermi surface detected in electron-doped materials is shown to sharply enhance the Nernst signal close to optimal doping. Within a semiclassical treatment, the obtained magnitude and position of the enhanced Nernst signal agrees with Nernst measurements in electron-doped cuprates.Comment: 9 pages, 5 figures, revised version as accepted by Phys. Rev. B, changed several citations and reference

Res iudicata pro veritate accipitur? Die Ziele des römischen Zivilprozesses zwischen Verhandlungsmaxime und Untersuchungsgrundsatz

Soll das Urteil für die Wahrheit genommen werden und damit inter omnes, auch Dritten gegenüber wirken, dann widerspricht dies der Beschränkung der Rechtskraft des Zivilurteils auf die Parteien und deren Rechtsnachfolger. Diese Beschränkung gilt für Streitigkeiten inter partes, zwischen zwei Parteien über Vermögensrechte. Dort herrscht das aus der Verhandlungsmaxime folgende Prinzip der nur formellen Wahrheit. Wegen des Anspruchs auf richterliches Gehör dürfen am Verfahren nicht beteiligte Dritte durch gewöhnliche Zivilurteile nicht benachteiligt werden. Für wahr gilt der Urteilsinhalt nur in nichtvermögensrechtlichen Verfahren mit Erforschung der materiellen Wahrheit durch den Richter von Amts wegen, insbesondere über den Personenstand. Die von Nikolaus Thaddäus Gönner um 1804 eingeführte Unterscheidung zwischen formeller und materieller Wahrheit, zwischen Verhandlungs- und Untersuchungsmaxime gehört zum Allgemeingut der gegenwärtigen Prozessrechtswissenschaft. Für das römische Prozessrecht werden Gönners Erkenntnisse im vorliegenden Beitrag hingegen erstmals fruchtbar gemacht

Smart Institutions for Smart Cities

Smart cities employ creativity of the population for innovations supporting social and economic development. In this context, this paper explores the role of framework conditions on special supply effects of university hospitals, which can invite further research institutions for intense collaboration, thereby stimulating innovations. The case study, comparing a hospital in Russia with one in Germany, is based on the concept of the employment multiplier. The results show that exogenously given, but, more importantly, also modifiable framework conditions lead to large differences regarding the employment multiplier. Thus, it should be the concern of smart cities to make smart use of their institutions, such as university hospitals, by adjusting the conditions, under which they are operating. © 2018 Institute of Physics Publishing. All rights reserved

Electron interactions and charge ordering in La2−x_{2-x}Srx_xCuO4_4

We present results of inelastic light scattering experiments on single-crystalline La$_{2-x}$Sr$_{x}$CuO$_4$ in the doping range $0.00 \le x=p \le 0.30$ and Tl$_2$Ba$_2$CuO$_{6+\delta}$ at $p=0.20$ and $p=0.24$. The main emphasis is placed on the response of electronic excitations in the antiferromagnetic phase, in the pseudogap range, in the superconducting state, and in the essentially normal metallic state at $x \ge 0.26$, where no superconductivity could be observed. In most of the cases we compare B$_{1g}$ and B$_{2g}$ spectra which project out electronic properties close to $(\pi,0)$ and $(\pi/2, \pi/2)$, respectively. In the channel of electron-hole excitations we find universal behavior in B$_{2g}$ symmetry as long as the material exhibits superconductivity at low temperature. In contrast, there is a strong doping dependence in B$_{1g}$ symmetry: (i) In the doping range $0.20 \le p \le 0.25$ we observe rapid changes of shape and temperature dependence of the spectra. (ii) In La$_{2-x}$Sr$_{x}$CuO$_4$ new structures appear for $x < 0.13$ which are superposed on the electron-hole continuum. The temperature dependence as well as model calculations support an interpretation in terms of charge-ordering fluctuations. For $x \le 0.05$ the response from fluctuations disappears at B$_{1g}$ and appears at B$_{2g}$ symmetry in full agreement with the orientation change of stripes found by neutron scattering. While, with a grain of salt, the particle-hole continuum is universal for all cuprates the response from fluctuating charge order in the range $0.05 \le p < 0.16$ is so far found only in La$_{2-x}$Sr$_{x}$CuO$_4$. We conclude that La$_{2-x}$Sr$_{x}$CuO$_4$ is close to static charge order and, for this reason, may have a suppressed $T_c$.Comment: 17 pages, 15 figure

A balancing act: Evidence for a strong subdominant d-wave pairing channel in Ba0.6K0.4Fe2As2{\rm Ba_{0.6}K_{0.4}Fe_2As_2}

We present an analysis of the Raman spectra of optimally doped ${\rm Ba_{0.6}K_{0.4}Fe_2As_2}$ based on LDA band structure calculations and the subsequent estimation of effective Raman vertices. Experimentally a narrow, emergent mode appears in the $B_{1g}$ ($d_{x^2-y^2}$) Raman spectra only below $T_c$, well into the superconducting state and at an energy below twice the energy gap on the electron Fermi surface sheets. The Raman spectra can be reproduced quantitatively with estimates for the magnitude and momentum space structure of the s$_{+-}$ pairing gap on different Fermi surface sheets, as well as the identification of the emergent sharp feature as a Bardasis-Schrieffer exciton, formed as a Cooper pair bound state in a subdominant $d_{x^2-y^2}$ channel. The binding energy of the exciton relative to the gap edge shows that the coupling strength in this subdominant $d_{x^2-y^2}$ channel is as strong as 60% of that in the dominant $s_{+-}$ channel. This result suggests that $d_{x^2-y^2}$ may be the dominant pairing symmetry in Fe-based sperconductors which lack central hole bands.Comment: 10 pages, 6 Figure

Electronic Raman Scattering in Nearly Antiferromagnetic Fermi Liquids

A theory of electronic Raman scattering in nearly antiferromagnetic Fermi liquids is constructed using the phenomenological electron-electron interaction introduced by Millis, Monien, and Pines. The role of "hot spots" and their resulting signatures in the channel dependent Raman spectra is highlighted, and different scaling regimes are addressed. The theory is compared to Raman spectra taken in the normal state of overdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$, and it is shown that many features of the symmetry dependent spectra can be explained by the theory.Comment: 3 pages + 4 figures, SNS97 Conference Proceeding

Cluster counting: The Hoshen-Kopelman algorithm vs. spanning tree approaches

Two basic approaches to the cluster counting task in the percolation and related models are discussed. The Hoshen-Kopelman multiple labeling technique for cluster statistics is redescribed. Modifications for random and aperiodic lattices are sketched as well as some parallelised versions of the algorithm are mentioned. The graph-theoretical basis for the spanning tree approaches is given by describing the "breadth-first search" and "depth-first search" procedures. Examples are given for extracting the elastic and geometric "backbone" of a percolation cluster. An implementation of the "pebble game" algorithm using a depth-first search method is also described.Comment: LaTeX, uses ijmpc1.sty(included), 18 pages, 3 figures, submitted to Intern. J. of Modern Physics