X. F. Sun

Low-temperature electronic heat transport in La2-xSrxCuO4 single crystals: unusual low-energy physics in the normal and superconducting states.

The thermal conductivity kappa is measured in a series of La2-xSrxCuO4 (0 < or = x < or = 0.22) single crystals down to 90 mK to elucidate the evolution of the residual electronic thermal conductivity kappa(res), which probes the extended quasiparticle states in the d-wave gap. We found that kappa(res)/T grows smoothly, except for a 1/8 anomaly, above x approximately 0.05, and shows no discontinuity at optimum doping, indicating that the behavior of kappa(res)/T is not governed by the metal-insulator crossover in the normal state; as a result, kappa(res)/T is much larger than what the normal-state resistivity would suggest in the underdoped region, which highlights the peculiarities in the low-energy physics in the cuprates.

Electronic inhomogeneity and breakdown of the universal thermal conductivity of cuprate superconductors.

We report systematic, high-precision measurements of the low-T (down to 70 mK) thermal conductivity kappa of YBa2Cu3O(y), La(2-x)Sr(x)CuO4, and Bi2Sr2CaCu2O(8+delta). Careful examinations of the Zn- and hole-doping dependences of the residual thermal conductivity kappa0/T, as well as the in-plane anisotropy of kappa0/T in Bi2Sr2CaCu2O(8+delta), indicate a breakdown of the universal thermal conductivity, a notable theoretical prediction for d-wave superconductors. Our results point to an important role of electronic inhomogeneities, which are not considered in the standard perturbation theory for thermal conductivity, in the underdoped to optimally doped regime.

Quantum Phase Transitions in the Cuprate Superconductor Bi~2Sr~2~-~xLa~xCuO~6~+~d~e~l~t~a

To elucidate a quantum phase transition (QPT) in Bi(2)Sr(2-x)La(x)CuO(6+delta), we measure charge and heat transport properties at very low temperatures and examine the following characteristics for a wide range of doping: normal-state resistivity anisotropy under 58 T, temperature dependence of the in-plane thermal conductivity kappa(ab), and the magnetic-field dependence of kappa(ab). It turns out that all of them show signatures of a QPT at the 1/8 hole doping. Together with the recent normal-state Hall measurements under 58 T that signified the existence of a QPT at optimum doping, the present results indicate that there are two QPTs in the superconducting doping regime of this material.

Adsorbate-induced spin-polarization enhancement of Fe3O4(0?0?1)

Using a spin-polarized metastable helium beam, we have investigated the remanent spin polarization at the surface of clean, hydrogen-terminated and benzene-adsorbed Fe3O4(0?0?1) thin films prepared on MgO(0?0?1) substrates. For the clean surface, a small negative asymmetry is detected in the ejected electron yields for helium-electron spins aligned parallel and anti-parallel to the sample magnetization direction. This confirms earlier experimental results from less surface-sensitive techniques which show that the spin polarization at the surface of Fe3O4(0?0?1) is much reduced from the bulk value and, furthermore, implies that majority-spin states actually dominate at the Fermi level. However, when hydrogen-terminated, the asymmetry is considerably enhanced and positive highlighting the important role that surface adsorption and passivation will play in the development of spintronic materials. This is further demonstrated for the adsorption of the simplest ?-conjugated molecule, benzene, at the clean Fe3O4(0?0?1) surface where a similar enhancement in the spin polarization is observed, an effect that could prove beneficial to the design and fabrication of organic spintronic devices.

Spin-glass state of individual magnetic vortices in YBa2Cu3Oy and La2- xSrxCuO4 below the metal-to-insulator crossover

Highly disordered magnetism confined to individual weakly interacting vortices is detected by muon spin rotation in two different families of high-transition-temperature superconductors, but only in samples on the low-doping side of the low-temperature normal state metal-to-insulator crossover (MIC). The results support an extended quantum phase transition (QPT) theory of competing magnetic and superconducting orders that incorporates the coupling between CuO2 planes. Contrary to what has been inferred from previous experiments, the static magnetism that coexists with superconductivity near the field-induced QPT is not ordered. Our findings unravel the mystery of the MIC and establish that the normal state of high-temperature superconductors is ubiquitously governed by a magnetic quantum critical point in the superconducting phase.

Phonon-glass-like behavior of magnetic origin in single-crystal Tb 2 Ti 2 O 7

Q. J. Li, Z. Y. Zhao, C. Fan, F. B. Zhang, H. D. Zhou, 3 X. Zhao, ∗ and X. F. Sun † Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306-4005, USA School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China (Dated: May 30, 2013)

Spin polarization study of graphene on the Ni(111) surface by density functional theory calculations with a semiempirical long-range dispersion correction

The geometric and spin-resolved electronic structure of a graphene-adsorbed Ni(111) surface has been investigated by density functional theory (DFT) calculations without and with a semiempirical long-range dispersion correction (DFT-D). DFT calculations with generalized gradient approximation (GGA) functional cannot predict well about the adsorption properties of graphene to the Ni(111) surface. While DFT-D calculations with the same GGA functional give reasonable values of the adsorption energy and layer distance from graphene to the substrate. The geometry of top_fcc is the most energetically favorable in all geometries. Strong hybridization of graphene with the ferromagnetic Ni substrate induces significant shift partially in graphene π states towards the Fermi level yielding spin polarization. The spin polarization is positive at the shallow levels of modified π states and slightly negative at the deeper levels of fundamental π states, which is indicated by the calculated spin density distributions an...

Energy-level alignment at the Alq3/Fe3O4(001) interface

We have used the technique of metastable de-excitation spectroscopy to probe the interfacial electronic structure of the organic semiconductor (OSC) Alq3 deposited onto clean Fe3O4(001) substrates. We have measured shifts in the low-energy secondary electron cutoff and energetic onset of the highest occupied molecular orbital (HOMO) of Alq3 as the coverage increases from the sub-ML range to multilayer formation. We find that the presence of an interfacial dipole induces a uniform decrease in the valence band electronic states by 1.2 eV with respect to the vacuum level and modifies the position of the HOMO energetic onset to 1.8 eV below the substrate Fermi level. The strong intrinsic dipole moment of Alq3 is suggested as the origin for these changes in accordance with previous studies of Alq3 deposited onto various substrates.

Low-temperature heat transport in the layered spin-dimer compound Ba 3 Mn 2 O 8

We report a study on the low-temperature heat transport of the Ba

Comment on Low-temperature phonon thermal conductivity of single-crystalline Nd2CuO4: Effects of sample size and surface roughness

{}_{3}