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Anomalies in the superconducting dome of the Bi-cuprates  [PDF]
L. Dudy,A. Krapf,H. Dwelk,S. Rogaschewski,B. Müller,O. Lübben,C. Janowitz,R. Manzke
Physics , 2010,
Abstract: We report characterization results by energy dispersive x-ray analysis and AC-susceptibility for a statistically relevant number of single layer Bi-cuprate single crystals. We show that the two structurally quite different modifications of the single-layered Bi-cuprate, namely (La,Pb=0.4)-Bi2201 and La-Bi2201, exhibit anomalies in the superconducting transition temperature at certain hole doping, e.g. at 1/8 holes per Cu. These doping values agree well with the 'magic doping fractions' found in the temperature dependent resistance of LSCO by Komiya et al. This new set of findings suggests that all these anomalies are generic for the hole-doped high-temperature superconductors.
Self-energy effects in cuprates and the dome-shaped behavior of the superconducting critical temperature  [PDF]
Guillermo Buzon,Adriana Foussats,Matías Bejas,Andrés Greco
Physics , 2014, DOI: 10.1103/PhysRevB.89.024516
Abstract: Hole doped cuprates show a superconducting critical temperature $T_c$ which follows an universal dome-shaped behavior as function of doping. It is believed that the origin of superconductivity in cuprates is entangled with the physics of the pseudogap phase. An open discussion is whether the source of superconductivity is the same that causes the pseudogap properties. The $t$-$J$ model treated in large-N expansion shows $d$-wave superconductivity triggered by non-retarded interactions, and an instability of the paramagnetic state to a flux phase or $d$-wave charge density wave ($d$-CDW) state. In this paper we show that self-energy effects near $d$-CDW instability may lead to a dome-shaped behavior of $T_c$. In addition, it is also shown that these self-energy contributions may describe several properties observed in the pseudogap phase. In this picture, although fluctuations responsible for the pseudogap properties leads to a dome-shaped behavior, they are not involved in pairing which is mainly non-retarded.
Local measurement of the superfluid density in the pnictide superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ across the superconducting dome  [PDF]
Lan Luan,Thomas M. Lippman,Clifford W. Hicks,Julie A. Bert,Ophir M. Auslaender,Jiun-Haw Chu,James G. Analytis,Ian R. Fisher,Kathryn A. Moler
Physics , 2010, DOI: 10.1103/PhysRevLett.106.067001
Abstract: We measure the penetration depth $\lambda_{ab}(T)$ in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ using local techniques that do not average over the sample. The superfluid density $\rho_s(T)\equiv1/\lambda_{ab}(T)^2$ has three main features. First, $\rho_s(T=0)$ falls sharply on the underdoped side of the dome. Second, $\lambda_{ab}(T)$ is flat at low $T$ at optimal doping, indicating fully gapped superconductivity, but varies more strongly in underdoped and overdoped samples, consistent with either a power law or a small second gap. Third, $\rho_s(T)$ varies steeply near $T_c$ for optimal and underdoping. These observations are consistent with an interplay between magnetic and superconducting phases.
Thermal Conductivity across the Phase Diagram of Cuprates: Low-Energy Quasiparticles and Doping Dependence of the Superconducting Gap  [PDF]
Mike Sutherland,D. G. Hawthorn,R. W. Hill,F. Ronning,S. Wakimoto,H. Zhang,C. Proust,Etienne Boaknin,C. Lupien,Louis Taillefer,Ruixing Liang,D. A. Bonn,W. N. Hardy,Robert Gagnon,N. E. Hussey,T. Kimura,M. Nohara,H. Takagi
Physics , 2003, DOI: 10.1103/PhysRevB.67.174520
Abstract: Heat transport in the cuprate superconductors YBa$_2$Cu$_3$O$_{y}$ and La$_{2-x}$Sr$_x$CuO$_4$ was measured at low temperatures as a function of doping. A residual linear term kappa_{0}/T is observed throughout the superconducting region and it decreases steadily as the Mott insulator is approached from the overdoped regime. The low-energy quasiparticle gap extracted from kappa_{0}/T is seen to scale closely with the pseudogap. The ubiquitous presence of nodes and the tracking of the pseudogap shows that the overall gap remains of the pure d-wave form throughout the phase diagram, which excludes the possibility of a complex component (ix) appearing at a putative quantum phase transition and argues against a non-superconducting origin to the pseudogap. A comparison with superfluid density measurements reveals that the quasiparticle effective charge is weakly dependent on doping and close to unity.
Phase competition in trisected superconducting dome  [PDF]
I. M. Vishik,M Hashimoto,R. -H. He,W. S. Lee,F. Schmitt,D. H. Lu,R. G. Moore,C. Zhang,W. Meevasana,T. Sasagawa,S. Uchida,K. Fujita,S. Ishida,M. Ishikado,Y. Yoshida,H. Eisaki,Z. Hussain,T. P. Devereaux,Z. -X. Shen
Physics , 2012, DOI: 10.1073/pnas.1209471109
Abstract: A detailed phenomenology of low energy excitations is a crucial starting point for microscopic understanding of complex materials such as the cuprate high temperature superconductors. Because of its unique momentum-space discrimination, angle-resolved photoemission spectroscopy (ARPES) is ideally suited for this task in the cuprates where emergent phases, particularly superconductivity and the pseudogap, have anisotropic gap structure in momentum space. We present a comprehensive doping-and-temperature dependence ARPES study of spectral gaps in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212), covering much of the superconducting portion of the phase diagram. In the ground state, abrupt changes in near-nodal gap phenomenology give spectroscopic evidence for two potential quantum critical points, p$=$0.19 for the pseudogap phase and p$=$0.076 for another competing phase. Temperature dependence reveals that the pseudogap is not static below T$_c$ and exists p$>$0.19 at higher temperatures. Our data imply a revised phase diagram which reconciles conflicting reports about the endpoint of the pseudogap in the literature, incorporates phase competition between the superconducting gap and pseudogap, and highlights distinct physics at the edge of the superconducting dome.
Evolution of a bosonic mode across the superconducting dome in the high-Tc cuprate Pr(2-x)Ce(x)CuO(4-δ)  [PDF]
Itay Diamant,Shay Hacohen-Gourgy,Yoram Dagan
Physics , 2011, DOI: 10.1103/PhysRevB.84.104511
Abstract: We report a detailed spectroscopic study of the electron doped cuprate superconductor Pr(2-x)Ce(x)CuO(4-{\delta}) using point contact junctions for x=0.125(underdoped), x=0.15(optimally doped) and x=0.17(overdoped). From our conductance measurements we are able to identify bosonic resonances for each doping. These excitations disappear above the critical temperature, and above the critical magnetic field. We find that the energy of the bosonic excitations decreases with doping, which excludes lattice vibrations as the paring glue. We conclude that the bosonic mediator for these cuprates is more likely to be spin excitations.
Micro-Raman evidence for topological charge order across the superconducting dome of La_{2-x)SrxCuO4  [PDF]
D. Lampakis,E. Liarokapis,C. Panagopoulos
Physics , 2009, DOI: 10.1103/PhysRevB.73.174518
Abstract: The doping dependence of the micro-Raman spectra of high quality La_{2-x}Sr_xCuO_4 microcrystals with x=0.0-0.45 has been investigated in the region 10-300 K. The phonon at ~100 cm^{-1} of the orthorhombic phase shows a classical soft mode behavior up to x=0.17, supporting its correlation with the LTO to HTT transition. In the xx/yy polarization spectra of the superconducting concentrations new modes at ~150 and 370 cm^{-1} related to the symmetry breaking and a broad band at ~280 cm^{-1} are attributed to the charge ordering at temperatures well above T_c. At all temperatures studied a correlation has been found between the doping dependence of the transition temperature and the intensity of the bands at ~150, ~280, ~370 cm^{-1}, the intensity of the La/Sr mode, and the asymmetry of the apex phonon.
Superconducting Dome from Holography  [PDF]
Suman Ganguli,Jimmy A. Hutasoit,George Siopsis
Physics , 2013, DOI: 10.1103/PhysRevD.87.126003
Abstract: We find a regime in which a strongly coupled striped superconductor features a superconducting dome. This regime is signified by i) a modulating chemical potential that averages to zero, and ii) a superconducting order parameter that has a scaling dimension larger than 3/2 but less than or equal to 3. We also find that in this regime, the order parameter exhibits a mild dependence on the modulation wavelength of the stripe.
Doping-driven transition to a time-reversal breaking state in the phase diagram of the cuprates  [PDF]
G. Sangiovanni,M. Capone,S. Caprara,C. Castellani,C. Di Castro,M. Grilli
Physics , 2001, DOI: 10.1103/PhysRevB.67.174507
Abstract: Motivated by recent tunnelling and Andreev-reflection experiments, we study the conditions for a quantum transition within the superconducting phase of the cuprates,in which a bulk imaginary (time-reversal breaking) $id_{xy}$component appears in addition to the $d_{x^2 - y^2}$ order parameter. We examine in detail the role of some important physical features of the cuprates.In particular we show that a closed Fermi surface,a bilayer splitting, an orthorhombic distortion,and the proximity to a quantum critical point around optimal doping favor the appearance of the imaginary component. These findings could explain why the mixed $d_{x^2 - y^2}+ id_{xy}$ order parameter is observed in YBCO and LSCO, and suggest that it could appear also in Bi2212. We also predict that, in all cuprates, the mixed state should be stable only in a limited doping region all contained beneath the $d_{x^2 - y^2}$ dome. The behavior of the specific heat at the secondary transition is discussed.
Quantum critical point lying beneath the superconducting dome in iron-pnictides  [PDF]
T. Shibauchi,A. Carrington,Y. Matsuda
Physics , 2013, DOI: 10.1146/annurev-conmatphys-031113-133921
Abstract: Whether a quantum critical point (QCP) lies beneath the superconducting dome has been a long-standing issue that remains unresolved in many classes of unconventional superconductors, notably cuprates, heavy fermion compounds and most recently iron-pnictides. The existence of a QCP may offer a route to understand: the origin of their anomalous non-Fermi liquid properties, the microscopic coexistence between unconventional superconductivity and magnetic or some exotic order, and ultimately the mechanism of superconductivity itself. The isovalent substituted iron-pnictide BaFe$_2$(As$_{1-x}$P$_x$)$_2$ offers a new platform for the study of quantum criticality, providing a unique opportunity to study the evolution of the electronic properties in a wide range of the phase diagram. Recent experiments in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ have provided the first clear and unambiguous evidence of a second order quantum phase transition lying beneath the superconducting dome.
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