Electronic specific heat and low-energy quasiparticle excitations in the superconducting state ofLa2−xSrxCuO4

Abstract

Low temperature specific heat has been measured and extensively analyzed on a series of La2−xSrxCuO4 single crystals from underdoped to overdoped regime. From these data the quasiparticle density of states (DOS) in the mixed state is derived and compared to the predicted scaling lawIt is found that the scaling law can be nicely followed by the optimally doped sample (x=0.15) in quite wide region of (T / √ H ≤ 8K/ √ T ). However, the region for this scaling becomes smaller and smaller towards more underdoped region: a clear trend can be seen for samples from x= 0.15 to 0.069. Therefore, generally speaking, the scaling quality becomes worse on the underdoped samples in terms of scalable region of T / √ H. This feature in the underdoped region is explained as due to the low energy excitations from a second order (for example, anti-ferromagnetic correlation, d-density wave, spin density wave or charge density wave order) that may co-exist or compete with superconductivity. Surprisingly, deviations from the d-wave scaling law have also been found for the overdoped sample (x=0.22). While the scaling law is reconciled for the overdoped sample when the core size effect is taken into account. An important discovery of present work is that the zero-temperature data follow the Volovik's relation ∆γ(T = 0) = A √ H quite well for all samples investigated here although the applicability of the d-wave scaling law to the data at finite temperatures varies with doped hole concentration. Finally we present the doping dependence of some parameters, such as, the residual linear term γ0, the α value, etc. It is suggested that the residual linear term (γ0T ) of the electronic specific heat observed in all cuprate superconductors is probably due to the inhomogeneity, either chemical or electronic in origin. The field induced reduction of the specific heat in the mixed state is also reported. Finally implications on the electronic phase diagram are suggested.

Multiple-Valued Memory Operation Using a Single-Electron Device: a Proposal and an Experimental Demonstration of a Ten-Valued Operation

“…As shown in figure 7, almost all the points fall within ±10% of a horizontal straight line, consistent with the results reported for the d-wave superconductors, YBCO [14,15] and LSCO [17][18][19]. So we can say that the MTG-YBa 2 Cu 2.99 Li 0.01 O x crystal is a d-wave superconductor.…”

“…The scaling law has been verified in YBa 2 Cu 3 O 7 (YBCO) [14][15][16] and La 2−x Sr x CuO 4 (LSCO) [10,[17][18][19], and even in other materials, such as Pr 1.85 Ce 0.15 CuO 4 (PCCO) [20].…”

Real-time measurement of the emergence of superconducting order in a high-temperature superconductor

“…where γ e = 2.5mJ/mol/K 2 [30] is electronic specific heat coefficient, γ ij represents the coupling between the ith and jth bath, T i is the temperature of the corresponding system (indices e, p and l are for electronic, hot boson and lattice, respectively), and P (t) = F 2πω exp (−t/2w 2 ) exp (−z/λ) is the optical excitation, w = 60 f s is the pulse width at half maximum. We also assume that total phonon heat capacity C = C p + C l , where C p = αC 0 and C l = (1 − α)C 0 is heat capacity of hot bosons and the lattice bath, respectively, α = 0.2 is a fraction of the phonons modes which are strongly coupled to electrons.…”

Evidence for multiple gaps in the specific heat of LiFeAs crystals

“…Large ␥ 0 has been observed in both cuprates and FeAs-based superconductors. 7,20 Contributions from isolated "normal" inclusions have been widely accepted as its origin. The carriers within such inclusions may not take part in superconductive condensation and lead to a nonzero ␥ 0 .…”