We present a study of the thermoelectric (Seebeck and Nernst) response in heavily overdoped, non-superconducting La_1.67Sr_0.33CuO_4. In spite of the electron-like curvature of the Fermi surface, the Seebeck coefficient is positive at low temperatures. Such a feature, previously observed in copper, silver, gold and lithium, is caused by a non-trivial energy dependence of the scattering time. We argue that this feature implies a strong asymmetry between the lifetime of occupied and unoccupied states along the zone diagonals and such an electron-hole asymmetry impedes formation of Cooper pairs along the nodal direction in the superconducting ground state emerging at lower doping levels.

Recent research into applications of the Leidenfrost effect have sparked renewed interest for this phenomenon. We report here on some of these developments, and on their deployment in an undergraduate teaching project that culminated in the production of a viral internet video. We analyse the key ingredients to the project's apparent success, both in terms of physics pedagogy and outreach/public engagement.

The introduction of technology-enabled interactive problem solving sequences involving peer and class-wide instruction in a Mathematics for scientists module is presented. While traditional chalk-and-talk is mainly used in lecturing, the combined use of an electronic audience response system and a digital pen-and-pad visualiser in problem classes leads to increased student engagement and interaction, in an informal and occasionally playful setting. This provides an opportunity for the lecturer to provide immediate targeted formative feedback that points the students to the fundamental concepts underlying the exercises.

Submitted for the MAR07 Meeting of The American Physical Society Frustrated metallicity in the quasi-one-dimensional conductor PrBa2Cu4O8 ALESSANDRO NARDUZZO, ARAZ ENAYATI-RAD, University of Bristol, FLORENCE RULLIER-ALBENQUE, SPEC, CEA, Paris, SHIGERU HORII, University of Tokyo, NIGEL HUSSEY, University of Bristol — We have investigated the ground state of the extremely anisotropic quasi-one-dimensional metal PrBa2Cu4O8 (t 2 b : t 2 a : t 2 c ∼ 4000 : 2 : 1), the nonsuperconducting analogue of the high-Tc cuprate YBa2Cu4O8, as a function of disorder content, introduced either through atomic-site substitution or electron irradiation. A common single disorder threshold is found to drive interchain and in-chain resistivities into a low temperature regime where they display dρ/dT < 0. The survival of a large magnetoresistance of orbital origin reveals the itinerancy of the electronic system not to be suppressed by the presence of disorder. We propose an interpretative scenario based on a microscopic fragmentation of the metallic chains, though in contrast to many previous theoretical proposals, coherent hopping between chains appears to remain a relevant perturbation within the disordered system. Alessandro Narduzzo University of Bristol Date submitted: 20 Nov 2006 Electronic form version 1.4

This article reports on a Writing in the Disciplines (WiD) intervention for first year undergraduate physics (and joint Honours) students. A short (200-250 word) assignment was designed to maximise students’ learning of specific scientific writing practices, including writing with appropriate clarity and academic style for a target audience, incorporating mathematical expressions in text, creating diagrams and referring to them in text, and appropriately using citing and referencing. Peer marking was employed to offer students formative feedback before they completed the assignment. The success of the assignment as a vehicle for student learning was evaluated by reviewing the students’ submissions and marks awarded, and through ten students’ reported focus group responses to the experience of carrying out the assignment, their reaction to peer marking, and their responses to the assessor’s written and verbal feedback. The effectiveness of the assignment’s content and process, and the peer marking, are briefly discussed, and suggestions made as to how to improve this or similar assignments in future years.

V. paper■show (5) and... I. Aim To enhance maths learning by facilitating student interaction and peer instruction in problem classes using Turning PointTM audience response systems -“clickers”and Paper■ShowTM digital –“optical”pen(#). Chalk, Talk, Digital Pens and Audience Response Systems Combining tradition and technology to improve maths learning Alessandro Narduzzo, Department of Physics, University of Bath, A.Narduzzo@bath.ac.uk Nitin Parmar, Learning & Teaching Enhancement Office, University of Bath, N.R.Parmar@bath.ac.uk

In the quasi-one-dimensional cuprate PrBa2Cu4O8, the Pr cations order antiferromagnetically at 17 K in zero field. Through a combination of magnetic susceptibility, torque magnetometry, specific heat, and interchain transport measurements, the anisotropic temperature-magnetic-field phase diagram associated with this ordering has been mapped out. A low-temperature spin-flop transition in the Pr sublattice is found to occur at the same magnetic field strength and orientation as a dimensional crossover in the ground state of the metallic-CuO chains. This coincidence suggests that the spin reorientation is driven by a change in the anisotropic Rudermann-Kittel-Kasuya-Yosida interaction induced by a corresponding change in effective dimensionality of the conduction electrons.

We present the first comprehensive derivation of the intrinsic electronic phase diagram of the iron-oxypnictide superconductors in the normal state based on the analysis of the electrical resistivity ρ of both LaFeAsO_1-xF_x and SmFeAsO_1-xF_x for a wide range of doping. Our data give clear-cut evidence for unusual normal state properties in these new materials. In particular, the emergence of superconductivity at low doping levels is accompanied by distinct anomalous transport behavior in ρ of the normal state which is reminiscent of the spin density wave (SDW) signature in the parent material. At higher doping levels ρ of LaFeAsO_1-xF_x shows a clear transition from this pseudogap-like behavior to Fermi liquid-like behavior, mimicking the phase diagram of the cuprates. Moreover, our data reveal a correlation between the strength of the anomalous features and the stability of the superconducting phase. The pseudogap-like features become stronger in SmFeAsO_1-xF_x where superconductivity is enhanced and vanish when superconductivity is reduced in the doping region with Fermi liquid-like behavior.

Temperature-dependent and magnetic-field-dependent measurements of the microwave surface impedance of superconducting ${\text{LaFeAsO}}_{0.9}{\text{F}}_{0.1}$ $({T}_{c}\ensuremath{\approx}26\text{ }\text{K})$ reveal a very large upper critical field $({B}_{c2}\ensuremath{\approx}56\text{ }\text{T})$ and a large value of the depinning frequency $({f}_{0}\ensuremath{\approx}6\text{ }\text{GHz})$; together with an upper limit for the effective London penetration depth, ${\ensuremath{\lambda}}_{\text{eff}}\ensuremath{\le}200\text{ }\text{nm}$, our results indicate a strong similarity between this system and the high-${T}_{c}$ superconducting cuprates.

We report upper critical field Bc2(T) data for disordered (arsenic-deficient) LaO0.9F0.1FeAs1-delta in a wide temperature and magnetic field range up to 47 T. Because of the large linear slope of Bc2 approximately -5.4 to -6.6 T/K near Tc approximately 28.5 K, the T dependence of the in-plane Bc2(T) shows a flattening near 23 K above 30 T which points to Pauli-limited behavior with Bc2(0) approximately 63-68 T. Our results are discussed in terms of disorder effects within [corrected] unconventional superconducting pairings.

Root of a Carbon nanotube on the sub-strate with elongated catalyst particle Rolled up AlGaAs/Cr/Pt microtube Corrosion pit generated on a shot-peened Zr-based bulk metallic glass Lattice structure of a typical edge-shared chain cuprate: Li 2 CuO 2 In February 2008, a paper appeared showing superconductivity in a layered iron arse-nide material with a transition temperature (T c) of 26K[1]. This discovery has triggered an enormous amount of research activities all over the world. Meanwhile there are more than 500 papers dealing with this new class of high temperature superconductors. At first glance the story looks very similar to that of the cuprates: There are non-superconduct-ing antiferromagnetic parent compounds, as e.g. LaOFeAs, the parent compound of the so-called '1111' structure. The systems become superconducting upon doping, for example by replacing some of the oxygen in LaOFeAs by fluorine. Also the crystal structures of the new superconductors are somehow reminiscent of the cuprates, with layers of FeAs separated by spacer layers, such as LaO, where the dopants are introduced (Fig.). However , looking in more detail on the physical properties reveals pronounced differences between pnictides and cuprates. For example, the parent compounds of the pnictides are not Mott insulators but 'bad metals' with a spin density wave state [2,3]. Moreover, comparing experimental data to DFT calculations suggests that electron correlations are less important in the pnictides. On the other hand, there are good arguments, that the superconductivity in the pnictides can not be explained within the frame of a conventional electron phonon scenario. Meanwhile there is a whole family of pnictide superconductors. The highest critical temperatures are obtained by substituting La with smaller rare earths, at present the maximum T c amounts to about 54 K in the Sm based 1111 compound [4]. A simpler class of materials based on the BaFe 2 As 2 parent compound (the '122' structure, Fig. right) that does not have the LaO spacer layers also superconducts with a comparable T c [5]. More recently, superconductivity has been discovered in even simpler LiFeAs '111' and FeSe materials [6,7]. The race is therefore on, just as for the cuprates, to discover materials with increasingly higher T c. At the IFW, research on the pnictides superconductors started in April 2008 and meanwhile there are more than 20 papers on this topic dealing with (i) the synthesis of bulk materials and thin films, (ii) experimental studies of superconductivity and …

TT 32.1 Thu 14:00 Poster B Matrix product state approach for a two-lead, multi-level Anderson impurity model — •Andreas Holzner1,2, Andreas Weichselbaum2, and Jan von Delft2 — 1Institute for Theoretical Physics C, RWTH Aachen, D-52056 Aachen, Germany — 2Physics Department, Arnold Sommerfeld Center for Theoretical Physics, and Center for NanoScience, Ludwig-Maximilians-Universität München, D-80333 München, Germany

Magnetotransport measurements on the overdoped cuprate La1.7Sr0.3CuO4 are fitted using the Ong construction [Phys. Rev. B 43, 193 (1991)] and band parameters inferred from angle-resolved photoemission. Within a band picture, the low-temperature Hall data can only be fitted satisfactorily by invoking strong basal-plane anisotropy in the mean free path l. This violation of the isotropic-l approximation supports a picture of dominant small-angle elastic scattering in cuprates due to out-of-plane substitutional disorder. We conjecture that both band anisotropy and anisotropy in the elastic-scattering channel strongly renormalize the Hall coefficient in La2-xSrxCuO4 across the entire overdoped regime.

In the chain compound PrBa2Cu4O8 localization appears simultaneously with a dimensional crossover in the electronic ground state when the scattering rate in the chains exceeds the hopping rate between the chains. Here we report the discovery of a large, transverse magnetoresistance in PrBa2Cu4O8 in the localized regime. This result suggests a novel form of localization whereby electrons retain their metallic (quasi-one-dimensional) character over a microscopic length scale despite the fact that, macroscopically, they exhibit localized (one-dimensional) behavior.

The anisotropic resistivity of PrBa2Cu4O8 has been measured as a function of electron irradiation fluence. Localization effects are observed for extremely small amounts of disorder corresponding to electron mean free paths of order 100 unit cells. Estimates of the localization corrections suggest that this anomalous localization threshold heralds a crossover to a ground state with pronounced one-dimensional character in which conduction electrons become confined to a small cluster of chains.

Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4 are fitted using the Ong construction and band parameters inferred from angle-resolved photoemission. Within a band picture, the low temperature Hall data can only be fitted satisfactorily by invoking strong basal-plane anisotropy in the mean-free-path $\ell$. This violation of the isotropic-$\ell$ approximation supports a picture of dominant small-angle elastic scattering in cuprates due to out-of-plane substitutional disorder. We show that both band anisotropy and anisotropy in the elastic scattering channel strongly renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide doping and temperature range.