Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Evidence for nodal superconductivity in LaFePO  [PDF]
J. D. Fletcher,A. Serafin,L. Malone,J. Analytis,J-H Chu,A. S. Erickson,I. R. Fisher,A. Carrington
Physics , 2008, DOI: 10.1103/PhysRevLett.102.147001
Abstract: In several iron-arsenide superconductors there is strong evidence for a fully gapped superconducting state consistent with either a conventional s-wave symmetry or an unusual $s_\pm$ state where there the gap changes sign between the electron and hole Fermi surface sheets. Here we report measurements of the penetration depth $\lambda(T)$ in very clean samples of the related iron-phosphide superconductor, LaFePO, at temperatures down to $\sim$ 100 mK. We find that $\lambda(T)$ varies almost perfectly linearly with $T$ strongly suggesting the presence of gap nodes in this compound. Taken together with other data, this suggests the gap function may not be generic to all pnictide superconductors.
Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3  [PDF]
H. Kotegawa,T. Kawazoe,H. Tou,K. Murata,H. Ogino,K. Kishio,J. Shimoyama
Physics , 2009, DOI: 10.1143/JPSJ.78.123707
Abstract: We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.
Nodal superconductivity in FeS: Evidence from quasiparticle heat transport  [PDF]
T. P. Ying,X. F. Lai,X. C. Hong,Y. Xu,L. P. He,J. Zhang,M. X. Wang,Y. J. Yu,F. Q. Huang,S. Y. Li
Physics , 2015,
Abstract: We report low-temperature heat transport measurements on the newly discovered superconducting iron sulfide FeS with $T_c \approx$ 5 K, which has the same crystal structure and similar electronic band structure to the superconducting iron selenide FeSe. In zero magnetic field, a significant residual linear term $\kappa_0/T$, $\sim$30\% of its normal-state value, is observed. At low field, $\kappa_0/T$ increases rapidly with the increase of field. These results provide strong evidence for nodal superconducting gap in FeS. The origin of this nodal superconductivity in FeS is discussed, by comparing with other iron-based superconductors with nodal gap.
Extending Universal Nodal Excitations Optimizes Superconductivity in Bi2Sr2CaCu2O8+d  [PDF]
Aakash Pushp,Colin V. Parker,Abhay. N. Pasupathy,Kenjiro K. Gomes,Shimpei Ono,Jinsheng Wen,Zhijun Xu,Genda Gu,Ali Yazdani
Physics , 2009, DOI: 10.1126/science.1174338
Abstract: Understanding the mechanism by which d-wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed matter physics. Our high-resolution scanning tunneling microscopy measurements of the high transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+d show that samples with different Tcs in the low doping regime follow a remarkably universal d-wave low energy excitation spectrum, indicating a doping independent nodal gap. We demonstrate that Tc instead correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow this universal behavior. Increasing temperature above Tc turns the universal spectrum into an arc of gapless excitations, while overdoping breaks down the universal nodal behavior.
Evidence from Tunneling Spectroscopy for a Quasi-One Dimensional Origin of Superconductivity in Sr2RuO4  [PDF]
I. A. Firmo,S. Lederer,C. Lupien,A. P. Mackenzie,J. C. Davis,S. A. Kivelson
Physics , 2013, DOI: 10.1103/PhysRevB.88.134521
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 $0.1 T_C
Direct spectroscopic evidence for phase competition between the pseudogap and superconductivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$  [PDF]
Makoto Hashimoto,Elizabeth A. Nowadnick,Rui-Hua. He,Inna M. Vishik,Brian Moritz,Yu He,Kiyohisa Tanaka,Robert G. Moore,Donghui Lu,Yoshiyuki Yoshida,Motoyuki Ishikado,Takao Sasagawa,Kazuhiro Fujita,Shigeyuki Ishida,Shinichi Uchida,Hiroshi Eisaki,Zahid Hussain,Thomas P. Devereaux,Zhi-Xun Shen
Physics , 2014, DOI: 10.1038/nmat4116
Abstract: In the high-temperature ($T_{c}$) cuprate superconductors, increasing evidence suggests that the pseudogap, existing below the pseudogap temperature $T$*, has a distinct broken electronic symmetry from that of superconductivity. Particularly, recent scattering experiments on the underdoped cuprates have suggested that a charge ordering competes with superconductivity. However, no direct link of this physics and the important low-energy excitations has been identified. Here we report an antagonistic singularity at $T_{c}$ in the spectral weight of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+{\delta}}$ as a compelling evidence for phase competition, which persists up to a high hole concentration $p$ ~ 0.22. Comparison with a theoretical calculation confirms that the singularity is a signature of competition between the order parameters for the pseudogap and superconductivity. The observation of the spectroscopic singularity at finite temperatures over a wide doping range provides new insights into the nature of the competitive interplay between the two intertwined phases and the complex phase diagram near the pseudogap critical point.
Evidence for nodal superconductivity in quasi-one-dimensional K$_2$Cr$_3$As$_3$  [PDF]
G. M. Pang,M. Smidman,W. B. Jiang,J. K. Bao,Z. F. Weng,Y. F. Wang,L. Jiao,J. L. Zhang,G. H. Cao,H. Q. Yuan
Physics , 2015,
Abstract: The recent discovery of superconductivity in the quasi-one-dimensional compound K$_2$Cr$_3$As$_3$, which consists of double-walled tubes of [(Cr$_3$As$_3$)$^{2-}]^\infty$ that run along the c axis, has attracted immediate attention as a potential system for studying superconductors with reduced dimensionality. Here we report clear experimental evidence for the unconventional nature of the superconducting order parameter in K$_2$Cr$_3$As$_3$, by precisely measuring the temperature dependence of the change in the penetration depth $\Delta\lambda(T)$ using a tunnel diode oscillator. Linear behavior of $\Delta\lambda(T)$ is observed for $T\ll T_c$, instead of the exponential behavior of conventional superconductors, indicating that there are line nodes in the superconducting gap. This is strong evidence for unconventional behavior and may provide key information for identifying the pairing state of this novel superconductor.
The penetration depth in Sr2RuO4: Evidence for orbital dependent superconductivity  [PDF]
Hiroaki Kusunose,Manfred Sigrist
Physics , 2002, DOI: 10.1209/epl/i2002-00348-5
Abstract: The apparent $T^2$-temperature dependence of the London penetration depth in Sr$_2$RuO$_4$ is discussed on the basis of a multi-gap model with horizontal line nodes. The influence of the nodes in combination with nonlocal electromagnetic response leads to low-temperature behaviors as $-T^2\ln T$ in the London limit and as $T^2$ in the Pippard limit. These behaviors appear only at very low temperature. On the other hand, the interplay of the superconductivity of different bands is responsible for the observed $T^2$-like behavior over the wide temperature range. The experimental data can be fitted well with a set of material parameters as was used in the specific heat fitting.
Evidence for High-Temperature Superconductivity in Doped Laser-Processed Sr-Ru-O  [PDF]
A. M. Gulian,K. S. Wood,D. Van Vechten,J. Claassen,R. J. Soulen, Jr.,S. Qadri,M. Osofsky,A. Lucarelli,G. Luepke,G. R. Badalyan,V. S. Kuzanyan,A. S. Kuzanyan,V. R. Nikoghosyan
Physics , 2005,
Abstract: We have discovered that samples of a new material produced by special processing of crystals of Sr2RuO4 (which is known to be a triplet superconductor with Tc values ~1.0-1.5K) exhibit signatures of superconductivity (zero DC resistance and expulsion of magnetic flux) at temperatures exceeding 200K. The special processing includes deposition of a silver coating and laser micromachining; Ag doping and enhanced oxygen are observed in the resultant surface layer. The transition, whether measured resistively or by magnetic field expulsion, is broad. When the transition is registered by resistive methods, the critical temperature is markedly reduced when the measuring current is increased. The resistance disappears by about 190K. The highest value of Tc registered by magneto-optical visualization is about 220K and even higher values (up to 250K) are indicated from the SQUID-magnetometer measurements.
Evidence of nodal superconductivity in Na_0.35CoO2-1.3H_2O: a specific heat study  [PDF]
H. D. Yang,J. -Y. Lin,C. P. Sun,Y. C. Kang,C. L. Huang,K. Takada,T. Sasaki,H. Sakurai,E. Takayama-Muromachi
Physics , 2004, DOI: 10.1103/PhysRevB.71.020504
Abstract: Comprehensive low-temperature specific heat data C(T,H) of Na_0.35CoO2-1.3H_2O with temperature T down to 0.6 K and the magnetic field H up to 8 T are presented. For the normal state, the values of gamma_n=13.94 mJ/mol K2, and Debye temperature 362 K are reported. At zero field, a very sharp superconducting anomaly was observed at Tc=4.5 K with DeltaC/gamma_nTc=1.45. The superconducting volume fraction is estimated to be 47.4 % based on the consideration of entropy balance at Tc for the second-order superconducting phase transition. In the superconducting state, the electronic contribution C_es at H=0 can be well described by the model of the line nodal order parameter. In low H, gamma(H) H^1/2 which is also a manifestation of the line nodes. The behaviors of both Tc(H) and gamma(H) suggest the anisotropy of Hc2 or possible crossovers or transitions occurring in the mixed state.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.