tag:blogger.com,1999:blog-23540555886709922192017-02-08T20:45:07.645-08:00cond-mat.supr-con - SuperconductivitySite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger3110125tag:blogger.com,1999:blog-2354055588670992219.post-42127563993048036302013-08-06T00:03:00.029-07:002013-08-06T00:03:19.568-07:001110.6548 (K. V. Grigorishin et al.)<h2 class="title"><a href="http://arxiv.org/abs/1110.6548">Nonlocal free energy of a spatially inhomogeneous superconductor</a> [<a href="http://arxiv.org/pdf/1110.6548">PDF</a>]</h2>K. V. Grigorishin, B. I. Lev<a name='more'></a><blockquote class="abstract">The microscopic approach was developed for obtaining of the free energy of a superconductor with help direct calculation of the vacuum amplitude. The functional of free energy of the spatially inhomogeneous superconductor in a magnetic field was obtained with help the developed approach. The obtained functional is generalization of Ginzburg-Landau functionals for any temperature, for arbitrary spatial variations of the order parameter and for the nonlocality of the order parameter and the magnetic response. Moreover the nonlocality of the magnetic response is the consequence of the order parameter's nonlocality. The extremals of this functional are considered in the explicit form in the low-temperature limit and in the high-temperature limit at the condition of slowness of spatial variations of the order parameter.</blockquote>View original: <a href="http://arxiv.org/abs/1110.6548">http://arxiv.org/abs/1110.6548</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-41650338526165907232013-08-06T00:03:00.027-07:002013-08-06T00:03:18.371-07:001308.0601 (Shahaf Asban et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0601">Strong- versus Weak-Coupling Paradigms for Cuprate Superconductivity</a> [<a href="http://arxiv.org/pdf/1308.0601">PDF</a>]</h2>Shahaf Asban, Meni Shay, Muntaser Naamneh, Tal Kirzhner, Amit Keren<a name='more'></a><blockquote class="abstract">Absolute resistivity measurements as a function of temperature from optimally doped YBa_2Cu_3O_(7), La_(2-x)Sr_xCuO_4, Bi_2Sr_2CaCu_2O_(8-x), and (Ca_0.1La_0.9)(Ba_1.65La_0.35)Cu_3O_y thin films are reported. Special attention is given to the measurement geometrical factors and the resistivity slope between Tc and T^{*}. The results are compared with a strong coupling theory for the resistivity derivative near T_c, which is based on hard core bosons (HCB), and with several weak coupling theories, which are BCS based. Surprisingly, our results agree with both paradigms. The implications of these findings and the missing calculations needed to distinguish between the two paradigms are discussed.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0601">http://arxiv.org/abs/1308.0601</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-63168890210577112862013-08-06T00:03:00.025-07:002013-08-06T00:03:15.982-07:001308.0614 (Joseph Gezo et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0614">Stretched exponential spin relaxation in organic superconductors</a> [<a href="http://arxiv.org/pdf/1308.0614">PDF</a>]</h2>Joseph Gezo, Tak-Kei Lui, Brian Wolin, Charles P. Slichter, Russell Giannetta<a name='more'></a><blockquote class="abstract">Proton NMR measurements on the organic superconductor $\kappa-(ET)_2Cu[N(CN)_2]Br$ ($T_C = 11.6$ K) exhibit stretched exponential spin-lattice relaxation below $T\approx 25$ K, suggestive of an inhomogeneous magnetic phase that develops in the normal state and coexists with superconductivity. The onset of this phase coincides approximately with a large normal state Nernst signal reported previously. By contrast, the closely related superconductor $\kappa-(ET)_2Cu[(NCS)_2]Br$ ($T_C = 10.5$ K) shows single exponential spin-lattice relaxation and a conventional Nernst effect. The temperature range $T_C < T < 30$ K encompasses several phenomena in the $\kappa-(ET)_2X$ conductors, including changes in conduction electron spin resonance, electronic phase separation and the onset of antiferromagnetic order. Analogous behavior in $La_{2-x}Sr_xCuO_4$ suggests that a density wave may develop in $\kappa-(ET)_2Cu[N(CN)_2]Br$.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0614">http://arxiv.org/abs/1308.0614</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-33191972508245580532013-08-06T00:03:00.023-07:002013-08-06T00:03:15.303-07:001308.0664 (Tatsuya Kaneko et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0664">BCS-BEC crossover in the two-dimensional attractive Hubbard model:<br /> Variational cluster approach</a> [<a href="http://arxiv.org/pdf/1308.0664">PDF</a>]</h2>Tatsuya Kaneko, Yukinori Ohta<a name='more'></a><blockquote class="abstract">Variational cluster approximation is used to study the superconducting ground state in the two-dimensional attractive Hubbard model. We show that the calculated Bogoliubov quasiparticle spectra and condensation amplitude clearly exhibit the character of the Cooper pairs in momentum space and that the coherence length $\xi$ evaluated from the condensation amplitude demonstrates the smooth crossover from a weakly paired BCS state ($\xi\gg 1$) to a BEC state of tightly bound pairs ($\xi\ll 1$). The calculated kinetic and potential energies in the superconducting and normal ground states indicate that the superconducting state in the weak-coupling region is driven by the gain in potential energy, while in the strong-coupling region, it is driven by the gain in kinetic energy.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0664">http://arxiv.org/abs/1308.0664</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-56787486627875241252013-08-06T00:03:00.021-07:002013-08-06T00:03:14.254-07:001308.0694 (Denis Vasyukov et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0694">Scanning nano-SQUID with single electron spin sensitivity</a> [<a href="http://arxiv.org/pdf/1308.0694">PDF</a>]</h2>Denis Vasyukov, Yonathan Anahory, Lior Embon, Dorri Halbertal, Jo Cuppens, Lior Ne'eman, Amit Finkler, Yehonathan Segev, Yuri Myasoedov, Michael L. Rappaport, Martin E. Huber, Eli Zeldov<a name='more'></a><blockquote class="abstract">One of the critical milestones in the intensive pursuit of quantitative nanoscale magnetic imaging tools is achieving the level of sensitivity required for detecting the field generated by the spin magnetic moment {\mu}B of a single electron. Superconducting quantum interference devices (SQUIDs), which were traditionally the most sensitive magnetometers, could not hitherto reach this goal because of their relatively large effective size (of the order of 1 {\mu}m). Here we report self-aligned fabrication of nano-SQUIDs with diameters as small as 46 nm and with an extremely low flux noise of 50 n{\Phi}0/Hz^1/2, representing almost two orders of magnitude improvement in spin sensitivity, down to 0.38 {\mu}B/Hz^1/2. In addition, the devices operate over a wide range of magnetic fields with 0.6 {\mu}B/Hz^1/2 sensitivity even at 1 T. We demonstrate magnetic imaging of vortices in type II superconductor that are 120 nm apart and scanning measurements of AC magnetic fields down to 50 nT. The unique geometry of these nano-SQUIDs that reside on the apex of a sharp tip allows approaching the sample to within a few nm, which paves the way to a new class of single-spin resolved scanning probe microscopy.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0694">http://arxiv.org/abs/1308.0694</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-54407763584381923792013-08-06T00:03:00.019-07:002013-08-06T00:03:13.282-07:001308.0763 (Lixing You et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0763">Jitter analysis of a superconducting nanowire single photon detector</a> [<a href="http://arxiv.org/pdf/1308.0763">PDF</a>]</h2>Lixing You, Xiaoyan Yang, Yuhao He, Wenxing Zhang, Dengkuan Liu, Weijun Zhang, Lu Zhang, Ling Zhang, Xiaoyu Liu, Sijing Chen, Zhen Wang, Xiaoming Xie<a name='more'></a><blockquote class="abstract">Jitter is one of the key parameters for a superconducting nanowire single photon detector (SNSPD). Using an optimized time-correlated single photon counting system for jitter measurement, we extensively studied the dependence of system jitter on the bias current and working temperature. The signal-to-noise ratio of the single-photon-response pulse was proven to be an important factor in system jitter. The final system jitter was reduced to 18 ps by using a high-critical-current SNSPD, which showed an intrinsic SNSPD jitter of 15 ps. A laser ranging experiment using a 15-ps SNSPD achieved a record depth resolution of 3 mm at a wavelength of 1550 nm.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0763">http://arxiv.org/abs/1308.0763</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-37570609748844945112013-08-06T00:03:00.017-07:002013-08-06T00:03:12.325-07:001308.0865 (Y. -J. Chen et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0865">Doping evolution of Zhang-Rice singlet spectral weight: a comprehensive<br /> examination by x-ray absorption spectroscopy</a> [<a href="http://arxiv.org/pdf/1308.0865">PDF</a>]</h2>Y. -J. Chen, M. G. Jiang, C. W. Luo, J. -Y. Lin, K. H. Wu, J. M. Lee, J. M. Chen, Y. K. Kuo, J. Y. Juang, Chung-Yu Mou<a name='more'></a><blockquote class="abstract">The total spectral weight \textit{S} of the emergent low-energy quasipaticles in high-temperature superconductors is explored by x-ray absorption spectroscopy. In order to examine the applicability of the Hubbard model, regimes that cover from zero doping to overdoping are investigated. In contrast to mean field theory, we found that \textit{S} deviates from linear dependence on the doping level \textit{p}. The slope of \textit{S} versus \textit{p} changes continuously throughout the whole doping range with no sign of saturation up to \textit{p} = 0.23. Therefore, the picture of Zhang-Rice singlet remains intact within the most prominent doping regimes of HTSC's.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0865">http://arxiv.org/abs/1308.0865</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-16237815432884842752013-08-06T00:03:00.015-07:002013-08-06T00:03:11.476-07:001308.0894 (I. A. Firmo et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0894">Evidence from Tunneling Spectroscopy for a Quasi-One Dimensional Origin<br /> of Superconductivity in Sr2RuO4</a> [<a href="http://arxiv.org/pdf/1308.0894">PDF</a>]</h2>I. A. Firmo, S. Lederer, C. Lupien, A. P. Mackenzie, J. C. Davis, S. A. Kivelson<a name='more'></a><blockquote class="abstract">To establish the mechanism of unconventional superconductivity in Sr$_2$RUO$_4$, a prerequisite is direct information concerning the momentum-space structure of the energy gaps $\Delta_i(k)$, and in particular whether the pairing strength is stronger ("dominant") on the quasi-1D ($\alpha$ and $\beta$) or on the quasi-2D ($\gamma$) Fermi surfaces. We present scanning tunneling microscopy (STM) measurements of the density-of-states spectra in the superconducting state of Sr$_2$RuO$_4$ for $0.1 T_C<T<T_C$, and analyze them, along with published thermodynamic data, using a simple phenomenological model. We show that our observation of a single superconducting gap scale with maximum value $2\Delta \approx 5 T_C$ along with a spectral shape indicative of line nodes is consistent, within a weak-coupling model, with magnetically mediated odd-parity superconductivity generated by dominant, near-nodal Cooper pairing on the $\alpha$ and $\beta$ bands.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0894">http://arxiv.org/abs/1308.0894</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-71036380675548646172013-08-06T00:03:00.013-07:002013-08-06T00:03:10.425-07:001308.0915 (Roberto Brambilla et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0915">Critical state solution and AC loss computation of polygonally arranged<br /> thin superconducting tapes</a> [<a href="http://arxiv.org/pdf/1308.0915">PDF</a>]</h2>Roberto Brambilla, Francesco Grilli, Luciano Martini<a name='more'></a><blockquote class="abstract">The current density and field distributions in polygonally arranged thin superconducting tapes carrying AC current are derived under the assumption of the critical state model. Starting from the generic Biot-Savart law for a general polygonal geometry, we derive a suitable integral equation for the calculation of the current density and magnetic field in each tape. The model works for any transport current below $I_c$, which makes it attractive for studying cases of practical interest, particularly the dependence of AC losses on parameters such as the number of tapes, their distance from the center, and their separation.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0915">http://arxiv.org/abs/1308.0915</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-76659675827785764492013-08-06T00:03:00.011-07:002013-08-06T00:03:09.485-07:001308.0957 (Mikio Nakahara et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0957">Multiple Half-Quantum Vortices in Rotating Superfluid $^3$He</a> [<a href="http://arxiv.org/pdf/1308.0957">PDF</a>]</h2>Mikio Nakahara, Tetsuo Ohmi<a name='more'></a><blockquote class="abstract">Half-quantum votices and ordinary vortices in a rotating thin film superfluid $^3$He under a strong magnetic field are considered. It is shown that $2n+1$ half-quantum vortices interpolates between $n$ singular vortices and $n+1$ singular vortices as the angular velocity is changed. The phase diagram of the vortex configurations in the angular velocity-magnetic field space is obtained for a paramagnon parameter $\delta=0.05$.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0957">http://arxiv.org/abs/1308.0957</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-61086838340036608262013-08-06T00:03:00.009-07:002013-08-06T00:03:08.589-07:001308.0984 (A. Anghel)<h2 class="title"><a href="http://arxiv.org/abs/1308.0984">Geometrical Probability Distribution Functions for Cable-in-Conduit<br /> Conductors with Simply and Multiply Connected Cross-Sections</a> [<a href="http://arxiv.org/pdf/1308.0984">PDF</a>]</h2>A. Anghel<a name='more'></a><blockquote class="abstract">A geometrical method is presented for the calculation of the strand distribution functions for cable-in-conduit superconductors with simple and multiply connected cross-sections. The method is illustrated on different cable designs with simply and multiply connected structures.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0984">http://arxiv.org/abs/1308.0984</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-70571320840206428662013-08-06T00:03:00.007-07:002013-08-06T00:03:07.764-07:001308.0987 (Wei Chen et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0987">Implications of Resonant Inelastic X-ray Scattering Data for Theoretical<br /> Models of Cuprates</a> [<a href="http://arxiv.org/pdf/1308.0987">PDF</a>]</h2>Wei Chen, Oleg P. Sushkov<a name='more'></a><blockquote class="abstract">There are two commonly discussed points of view in theoretical description of cuprate superconductors, (i) Cuprates can be described by the modified t-J model. (ii) Overdoped cuprates are close to the regime of normal Fermi liquid (NFL). We argue that recent resonant inelastic X-ray scattering data challenge both points. While the modified t-J model describes well the strongly underdoped regime, it fails to describe high energy magnetic excitations when approaching optimal doping. This probably indicates failure of the Zhang-Rice singlet picture. In the overdoped regime the momentum-integrated spin structure factor S(\omega) has the same intensity and energy distribution as that in an undoped parent compound. This implies that the entire spin spectral sum rule is saturated at \omega ~ 2J, while in a NFL the spectral weight should saturate only at the total bandwidth which is much larger than 2J.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0987">http://arxiv.org/abs/1308.0987</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-63792406665497394682013-08-06T00:03:00.005-07:002013-08-06T00:03:06.741-07:001308.0995 (V. P. Mineev)<h2 class="title"><a href="http://arxiv.org/abs/1308.0995">Magnetostatics and optics of noncentrosymmetric metals</a> [<a href="http://arxiv.org/pdf/1308.0995">PDF</a>]</h2>V. P. Mineev<a name='more'></a><blockquote class="abstract">The current in noncentrosymmetric metals in normal and superconducting state is found in frame of linear response theory. In line with usual terms corresponding diamagnetic response, the Landau diamagnetism and the Pauli paramagnetism the general expression contains also the terms corresponding to spacial dispersion specific for a medium without space parity. This, so called, gyrotropic current is calculated in zero frequency case as well in infrared frequency region. The static gyrotropic current yields negligibly small correction to the London magnetostatics in a superconductor without inversion center. Whereas the high frequency response produces the natural-optical activity revealed f.e. in the Kerr effect. The magnitude of the Kerr angle in infrared frequency region is proved to be in reasonable correspondence with recently reported observations of the Kerr effect in the pseudogap phase in several different high Tc materials.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0995">http://arxiv.org/abs/1308.0995</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-21020386807430776632013-08-06T00:03:00.003-07:002013-08-06T00:03:05.718-07:001308.1040 (Wei Bao)<h2 class="title"><a href="http://arxiv.org/abs/1308.1040">Physics picture from neutron scattering study on Fe-based<br /> superconductors</a> [<a href="http://arxiv.org/pdf/1308.1040">PDF</a>]</h2>Wei Bao<a name='more'></a><blockquote class="abstract">Neutron scattering, with its ability to measure the crystal structure, the magnetic order, and the structural and magnetic excitations, plays an active role in investigating various families of Fe-based high-Tc superconductors. Three different types of antiferromag- netic orders have been discovered in the Fe plane, but two of them cannot be explained by the spin-density-wave (SDW) mechanism of nesting Fermi surfaces. Noticing the close relation between antiferromagnetic order and lattice distortion in orbital ordering from previous studies on manganites and other oxides, we have advocated orbital or- dering as the underlying common mechanism for the structural and antiferromagnetic transitions in the 1111, 122 and 11 parent compounds. We observe the coexistence of antiferromagnetic order and superconductivity in the (Ba,K)Fe2 As2 system, when its phase separation is generally accepted. Optimal Tc is proposed to be controlled by the local FeAs4 tetrahedron from our investigation on the 1111 materials. The Bloch phase coherence of the Fermi liquid is found crucial to the occurrence of bulk superconductiv- ity in iron chalcogenides of both the 11 and the 245 families. Iron chalcogenides carry a larger staggered magnetic moment (> 2{\mu}B /Fe) than that in iron pnictides (< 1{\mu}B /Fe) in the antiferromagnetic order. Normal state magnetic excitations in the 11 supercon- ductor are of the itinerant nature while in the 245 superconductor the spin-waves of localized moments. The observation of superconducting resonance peak provides a cru- cial piece of information in current deliberation of the pairing symmetry in Fe-based superconductors.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1040">http://arxiv.org/abs/1308.1040</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-17340987345033534902013-08-06T00:03:00.001-07:002013-08-06T00:03:04.582-07:001308.1072 (C. T. Wolowiec et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.1072">Enhancement of superconductivity near the pressure-induced<br /> semiconductor-metal transition in BiS2-based compounds LnO(0.5)F(0.5)BiS2 (Ln<br /> = La, Ce, Pr, Nd)</a> [<a href="http://arxiv.org/pdf/1308.1072">PDF</a>]</h2>C. T. Wolowiec, B. D. White, I. Jeon, D. Yazici, K. Huang, M. B. Maple<a name='more'></a><blockquote class="abstract">Measurements of electrical resistivity were performed as a function of temperature between 3 and 300 K at various pressures up to 2.8 GPa on the LnO0.5F0.5BiS2 (Ln = Pr, Nd) compounds. At low pressure, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 exhibit superconductivity with Tc of 3.5 and 3.9 K, respectively. Both compounds display semiconducting behavior at low pressure in the normal state which is strongly suppressed with pressure. Both compounds undergo a pressure-induced transition from a low Tc superconducting phase to a high Tc superconducting phase in which Tc reaches 7.6 and 6.4 K for PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced transition is characterized by a rapid increase in Tc within a small pressure range of ~0.3 GPa for both compounds. For PrO0.5F0.5BiS2, the transition pressure correlates with the pressure where the rate of suppression of semiconducting behavior in the normal state saturates. For NdO0.5F0.5BiS2, the transition pressure between superconducting phases corresponds to the pressure that induces a semiconductor-metal transition in the normal state. The suppression of semiconducting behavior and evolution of Tc with pressure in the compounds LnO0.5F0.5BiS2 (Ln = Pr, Nd) is markedly similar to behavior recently reported for the BiS2-based compounds LnO0.5F0.5BiS2 (Ln = La, Ce). [arXiv 1307.4157 (2013), Phys. Rev. B accepted] A plot of the transition pressure versus lanthanide element (Ln = La, Ce, Pr, Nd) indicates that there is an increase in the value of transition pressure with decrease in atomic radius of the lanthanide element in LnO0.5F0.5BiS2. In addition, the "jump" in Tc between the two superconducting phases becomes smaller with decrease in atomic radius of lanthanide element (Ln = La, Ce, Pr, Nd). We suspect that this behavior is a general characteristic of the BiS2-based family of layered superconductors LnO0.5F0.5BiS2.</blockquote>View original: <a href="http://arxiv.org/abs/1308.1072">http://arxiv.org/abs/1308.1072</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-82197293400726470432013-08-05T00:02:00.001-07:002013-08-05T00:02:08.763-07:001308.0537 (J. Murphy et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0537">Effect of heavy-ion irradiation on London penetration depth in<br /> over-doped Ba(Fe,Co)2As2</a> [<a href="http://arxiv.org/pdf/1308.0537">PDF</a>]</h2>J. Murphy, M. A. Tanatar, Hyunsoo Kim, W. Kwok, U. Welp, D. Graf, J. S. Brooks, S. L. Bud'ko, P. C. Canfield, R. Prozorov<a name='more'></a><blockquote class="abstract">Irradiation with 1.4 GeV $^{208}$Pb ions was used to induce artificial disorder in single crystals of iron-arsenide superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and to study its effect on the temperature-dependent London penetration depth and transport properties. Study was undertaken on overdoped single crystals with $x$=0.108 and $x$=0.127 characterized by notable modulation of the superconducting gap. Irradiation with doses 2.22$\times10^{11}$$\textit{d}$/cm$^2$ and 2.4$\times10^{11}$$\textit{d}$/cm$^2$, corresponding to the matching fields of $B_{\phi} = $6 T and 6.5 T, respectively, suppresses the superconducting $T_c$ by approximately 0.3 to 1 K. The variation of the low-temperature penetration depth in both pristine and irradiated samples is well described by the power-law, $\Delta \lambda (T)=AT^n$. Irradiation increases the magnitude of the pre-factor $A$ and decreases the exponent $n$, similar to the effect of irradiation in optimally doped samples. This finding supports universal $s_{\pm}$ pairing in Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ compounds for the whole Co doping range.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0537">http://arxiv.org/abs/1308.0537</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-870787257105197522013-08-04T00:03:00.005-07:002013-08-04T00:03:13.721-07:001308.0017 (Jacob Linder et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0017">Superconducting Proximity Effect in Silicene: Spin-Valley Polarized<br /> Andreev Reflection, Non-Local Transport, and Supercurrent</a> [<a href="http://arxiv.org/pdf/1308.0017">PDF</a>]</h2>Jacob Linder, Takehito Yokoyama<a name='more'></a><blockquote class="abstract">We theoretically study the superconducting proximity effect in silicene, which features massive Dirac fermions with a tunable mass (band gap), and compute the conductance across a normal/superconductor (N/S) silicene junction, the non-local conductance of an N/S/N junction, and the supercurrent flowing in an S/N/S junction. It is demonstrated that the transport processes consisting of local and non-local Andreev reflection may be efficiently controlled via an external electric field owing to the buckled structure of silicene. In particular, we demonstrate that it is possible to obtain a fully spin-valley polarized crossed Andreev reflection process without any contamination of elastic cotunneling or local Andreev reflection, in stark contrast to ordinary metals. It is also shown that the supercurrent flowing in the S/N/S junction can be fully spin-valley polarized and that it is controllable by an external electric field.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0017">http://arxiv.org/abs/1308.0017</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-68835940505282799672013-08-04T00:03:00.003-07:002013-08-04T00:03:12.712-07:001308.0138 (Arijit Saha)<h2 class="title"><a href="http://arxiv.org/abs/1308.0138">Electron-electron interaction effects on transport through mesoscopic<br /> superconducting hybrid junctions</a> [<a href="http://arxiv.org/pdf/1308.0138">PDF</a>]</h2>Arijit Saha<a name='more'></a><blockquote class="abstract">Effects due to the proximity of a superconductor has motivated a lot of research work in the last several decades both from theoretical and experimental point of view. In this review we are going to describe the physics of systems containing normal metal-superconductor interface. Mainly we discuss transport properties through such hybrid structures. In particular, we describe the effects of electron electron interaction on transport through such superconducting junction of multiple one-dimensional quantum wires. The latter can be described in terms of a non-Fermi liquid theory called Luttinger liquid. In this review, from the application point of view, we also demonstrate the possible scenarios for production of pure spin current and large tunnelling magnetoresistance in such hybrid junctions and analyze the influence of electron-electron interaction on the stability of the production of pure spin current.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0138">http://arxiv.org/abs/1308.0138</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-43678779648088114112013-08-04T00:03:00.001-07:002013-08-04T00:03:10.880-07:001308.0225 (Mohammad Hafezi et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0225">Engineering three-body interaction and Pfaffian states in circuit QED<br /> systems</a> [<a href="http://arxiv.org/pdf/1308.0225">PDF</a>]</h2>Mohammad Hafezi, Prabin Adhikari, Jacob M. Taylor<a name='more'></a><blockquote class="abstract">We demonstrate a scheme to engineer the three-body interaction in circuit-QED systems by tuning a fluxonium qubit. Connecting such qubits in a square lattice and controlling the tunneling dynamics, in the form of a synthesized magnetic field, for the photon-like excitations of the system, allows the implementation of a parent Hamiltonian whose ground state is the Pfaffian wave function. Furthermore, we show that the addition of the next-nearest neighbor tunneling stabilizes the ground state, recovering the expected topological degeneracy even for small lattices. Finally, we discuss the implementation of these ideas with the current technology.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0225">http://arxiv.org/abs/1308.0225</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-84689943549867872152013-08-02T00:45:00.001-07:002013-08-02T00:45:49.590-07:001301.7658 (Heron Caldas et al.)<h2 class="title"><a href="http://arxiv.org/abs/1301.7658">Nesting and lifetime effects in the FFLO state of quasi-one-dimensional<br /> imbalanced Fermi gases</a> [<a href="http://arxiv.org/pdf/1301.7658">PDF</a>]</h2>Heron Caldas, Mucio A. Continentino<a name='more'></a><blockquote class="abstract">Motivated by the recent experimental realization of a candidate to the Fulde-Ferrell (FF) and the Larkin-Ovchinnikov (LO) states in one dimensional (1D) atomic Fermi gases, we study the quantum phase transitions in these enigmatic, finite momentum-paired superfluids. We focus on the FF state and investigate the effects of the induced interaction on the stability of the FFLO phase in homogeneous spin-imbalanced quasi-1D Fermi gases at zero temperature. When this is taken into account we find a direct transition from the fully polarized to the FFLO state. Also, we consider the effect of a finite lifetime of the quasi-particles states in the normal-superfluid instability. In the limit of long lifetimes, the lifetime effect is irrelevant and the transition is directly from the fully polarized to the FFLO state. We show, however, that for sufficiently short lifetimes there is a quantum critical point (QCP), at a finite value of the mismatch of the Fermi wave-vectors of the different quasi-particles, that we fully characterize. In this case the transition is from the FFLO phase to a normal partially polarized state with increasing mismatch.</blockquote>View original: <a href="http://arxiv.org/abs/1301.7658">http://arxiv.org/abs/1301.7658</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-21650539458064928982013-08-01T00:32:00.007-07:002013-08-01T00:32:17.427-07:001307.8200 (H. Suzuki et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8200">Absence of Superconductivity in the "hole-doped" Fe pnictide<br /> Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$: Photoemission and X-ray Absorption<br /> Spectroscopy Studies</a> [<a href="http://arxiv.org/pdf/1307.8200">PDF</a>]</h2>H. Suzuki, T. Yoshida, S. Ideta, G. Shibata, K. Ishigami, T. Kadono, A. Fujimori, M. Hashimoto, D. H. Lu, Z. -X. Shen, K. Ono, E. Sakai, H. Kumigashira, M. Matsuo, T. Sasagawa<a name='more'></a><blockquote class="abstract">We have studied the electronic structure of Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x$=0.08), which fails to become a superconductor in spite of the formal hole doping like Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, by photoemission spectroscopy and X-ray absorption spectroscopy (XAS). With decreasing temperature, a transition from the paramagnetic phase to the antiferromagnetic phase was clearly observed by angle-resolved photoemission spectroscopy. XAS results indicated that the substituted Mn atoms form a strongly hybridized ground state. Resonance-photoemission spectra at the Mn $L_{3}$ edge revealed that the Mn 3d partial density of states is distributed over a wide energy range of 2-13 eV below the Fermi level ($E_F$), with little contribution around $E_F$. This indicates that the dopant Mn 3$d$ states are localized in spite of the strong Mn 3d-As $4p$ hybridization and split into the occupied and unoccupied parts due to the on-site Coulomb and exchange interaction. The absence of superconductivity in Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ can thus be ascribed both to the absence of carrier doping in the FeAs plane, and to the strong stabilizaiton of the antiferromagnetic order by the Mn impurities.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8200">http://arxiv.org/abs/1307.8200</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-39375776271616005712013-08-01T00:32:00.005-07:002013-08-01T00:32:16.501-07:001307.8264 (Simone Barbarino et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8264">Parity dependent Josephson current through a helical Luttinger liquid</a> [<a href="http://arxiv.org/pdf/1307.8264">PDF</a>]</h2>Simone Barbarino, Rosario Fazio, Maura Sassetti, Fabio Taddei<a name='more'></a><blockquote class="abstract">We consider a superconductor-two dimensional topological insulator- superconductor junction (S-2DTI-S) and study how the 2{\pi}- and 4{\pi}-periodic Josephson currents are affected by the electron-electron interaction. In the long-junction limit the supercurrent can by evaluated by modeling the system as a helical Luttinger liquid coupled to superconducting reservoirs. After having introduced bosonization in the presence of the parity constraint we turn to consider the limit of perfect and poor interfaces. For transparent interfaces, where perfect Andreev reflections occur at the boundaries, the Josephson current is marginally affected by the interaction. On the contrary, if strong magnetic scatterers are present in the weak link, the situation changes dramatically. Here Coulomb interaction plays a crucial role both in low and high temperature regimes. Furthermore, a phase-shift of Josephson current can be induced by changing the direction of the magnetization of the impurity.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8264">http://arxiv.org/abs/1307.8264</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-1466180342641661102013-08-01T00:32:00.003-07:002013-08-01T00:32:15.639-07:001307.8283 (P. Carretta et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8283">A view from inside iron-based superconductors</a> [<a href="http://arxiv.org/pdf/1307.8283">PDF</a>]</h2>P. Carretta, R. De Renzi, G. Prando, S. Sanna<a name='more'></a><blockquote class="abstract">Muon spin spectroscopy is one of the most powerful tools to investigate the microscopic properties of superconductors. In this manuscript, an overview on some of the main achievements obtained by this technique in the iron-based superconductors (IBS) are presented. It is shown how the muons allow to probe the whole phase diagram of IBS, from the magnetic to the superconducting phase, and their sensitivity to unravel the modifications of the magnetic and the superconducting order parameters, as the phase diagram is spanned either by charge doping, by an external pressure or by introducing magnetic and non-magnetic impurities. Moreover, it is highlighted that the muons are unique probes for the study of the nanoscopic coexistence between magnetism and superconductivity taking place at the crossover between the two ground-states.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8283">http://arxiv.org/abs/1307.8283</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-63126863321188532672013-08-01T00:32:00.001-07:002013-08-01T00:32:14.718-07:001307.8363 (Javier Rodríguez-Laguna et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8363">Energy space entanglement spectrum of pairing models with s-wave and<br /> p-wave symmetry</a> [<a href="http://arxiv.org/pdf/1307.8363">PDF</a>]</h2>Javier Rodríguez-Laguna, Miguel Ibáñez Berganza, Germán Sierra<a name='more'></a><blockquote class="abstract">Entanglement between blocks of energy-levels is analysed for systems exhibiting s-wave and p-wave superconductivity. We study the entanglement entropy and spectrum of a block of $\ell$ levels around the Fermi point, and also between particles and holes, in the ground state of Richardson-type Hamiltonians. The maximal entropy grows with the number of levels $L$ approximately as $1/2\log(L)$, as suggested by the permutational symmetry of the state at large coupling. The number of levels in the block around the Fermi surface with maximal entanglement is proposed as a measure of the number of {\em active Cooper pairs}, which correlates with standard estimates of this magnitude. The entanglement spectrum is always composed of a principal parabolic band plus {\em higher bands} whose disappearance signals a exact BCS state, e.g. in the Moore-Read line, while the Read-Green quantum phase transition is characterized by a maximum in their weight.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8363">http://arxiv.org/abs/1307.8363</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-2354055588670992219.post-86178810065461694432013-07-31T00:17:00.019-07:002013-07-31T00:17:59.802-07:001307.7719 (Shankar Iyer et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7719">Susceptibility at the Superfluid-Insulator Transition for<br /> One-Dimensional Disordered Bosons</a> [<a href="http://arxiv.org/pdf/1307.7719">PDF</a>]</h2>Shankar Iyer, David Pekker, Gil Refael<a name='more'></a><blockquote class="abstract">A pair of recent Monte Carlo studies have reported evidence for and against a crossover from weak to strong-disorder criticality in the one-dimensional dirty boson problem. The Monte Carlo analyses rely on measurement of two observables: the effective Luttinger parameter K_{eff} and the superfluid susceptibility chi. The former quantity was previously calculated analytically, using the strong-disorder renormalization group (SDRG), by Altman, Kafri, Polkovnikov, and Refael. Here, we use an extension of the SDRG framework to find a non-universal anomalous dimension eta_{sd} characterizing the divergence of the susceptibility with system size: chi ~ L^(2-eta_{sd}). We show that eta_{sd} obeys the hyperscaling relation eta_{sd} = 1/2K_{eff}. We also identify an important obstacle to measuring this exponent on finite-size systems and comment on the implications for numerics and experiments.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7719">http://arxiv.org/abs/1307.7719</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0