Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEvidence for two fluids in the ground state of cuprates
70
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report charge density measurements, using NMR, in the superconducting compound (Ca_{x}La_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_{y}, which has two independent variables x (family) and y (oxygen). For underdoped samples we find the rate at which holes are introduced into the plane upon oxygenation to be family-independent. In contrast, not all carriers contribute to either antiferromagnetic or superconducting order parameters. This result is consistent with a two fluid phenomenology or intrinsic mesoscopic inhomogeneities in the bulk. We also discuss the impact of weak-chemical-disorder on T_{c}.
rate research
Read More
Spontaneous vortex phase (SVP) is an exotic quantum matter in which quantized superconducting vortices form in the absence of external magnetic field. Although being predicted theoretically nearly 40 years ago, its rigorous experimental verification still appears to be lacking. Here we present low-field magnetic measurements on single crystals of the iron-based ferromagnetic superconductor Eu(Fe$_{0.91}$Rh$_{0.09}$)$_{2}$As$_{2}$ which undergoes a superconducting transition at $T_mathrm{sc}$ = 19.6 K followed by a magnetic transition at $T_mathrm{m}$ = 16.8 K. We observe a characteristic first-order transition from a Meissner state within $T_mathrm{m}<T<T_mathrm{sc}$ to an SVP below $T_mathrm{m}$, under a magnetic field approaching zero. Additional isothermal magnetization and ac magnetization measurements at $Tll T_mathrm{sc}$ confirm that the system is intrinsically in a spontaneous-vortex ground state. The unambiguous demonstration of SVP in the title material lays a solid foundation for future imaging and spectroscopic studies on this intriguing quantum matter.
Angle-resolved photoemission on underdoped La$_{1.895}$Sr$_{0.105}$CuO$_4$ reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of the Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity.
We discuss the stability of the antiferromagnetic ground state in two spatial dimensions. We start with a general analysis, based on Gribovs current-conservation techniques, of the bosonic modes in systems with magnetic order. We argue that the Goldstone $phi$ and Higgs $h$ modes mix in antiferromagnetic systems, and this leads to an effective $hhphi$ three-point interaction. We then analyze the instability of the antiferromagnetic system in two spatial dimensions by studying the non-perturbative behaviour of the Higgs boson self-energy using the Dyson--Schwinger equations. The ground state turns out to be unstable for all values of the three-point coupling. We interpret this as being due to the formation of a (high-$T_C$) superconducting condensate. The carrier doping dependence of the energy gap has a general behaviour that is consistent with high-$T_C$ superconductivity. Superconductivity co-exists with antiferromagnetic order for large magnetization, or small doping.
Preformed pairs above $T_c$ and the two-gap scenarios are two main proposals for describing the low doping pseudogap phase of high-$T_c$ cuprates. Very recent angle-resolved photoemission experiments have shown features which were interpreted as evidence for preformed pairs. Here it is shown that those results can be explained also in the context of the two-gap scenario if self-energy effects are considered. The discussion is based on the $d$-CDW theory or the flux phase of the $t-J$ model.
Anomalous metallic behavior, marked by a saturating finite resistivity much lower than the Drude estimate, has been observed in a wide range of two-dimensional superconductors. Utilizing the electrostatically gated LaAlO3/SrTiO3 interface as a versatile platform for superconductor-metal quantum phase transitions, we probe variations in the gate, magnetic field, and temperature to construct a phase diagram crossing from superconductor, anomalous metal, vortex liquid, to Drude metal states, combining longitudinal and Hall resistivity measurements. We find that the anomalous metal phases induced by gating and magnetic field, although differing in symmetry, are connected in the phase diagram and exhibit similar magnetic field response approaching zero temperature. Namely, within a finite regime of the anomalous metal state, the longitudinal resistivity linearly depends on field while the Hall resistivity diminishes, indicating an emergent particle-hole symmetry. The universal behavior highlights the uniqueness of the quantum bosonic metallic state, distinct from bosonic insulators and vortex liquids.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
