Direct observation and anisotropy of the contribution of gap nodes in the low-temperature specific heat ofYBa2Cu3

Abstract

The specific heat due to line nodes in the superconducting gap of YBa 2 Cu 3 O 7 has been blurred up to now by magnetic terms of extrinsic origin, even for high quality crystals. We report the specific heat of a new single crystal grown in a non-corrosive BaZrO 3 crucible, for which paramagnetic terms are reduced to ≈ 0.006% spin-1/2 per Cu atom. The contribution of line nodes shows up directly in the difference C(B, T ) − C(0, T ) at fixed temperatures (T < 5 K) as a function of the magnetic field parallel to the c-axis (B ≤ 14 T). These data illustrate the smooth crossover from C ∝ T 2 at low fields to C ∝ T B 1/2 at high fields, and provide new values for gap parameters which are quantitatively consistent with tunneling spectroscopy and thermal conductivity in the framework of d x 2 −y 2 pairing symmetry. Data for B along the nodal and antinodal directions in the ab-plane are also provided. The in-plane anisotropy predicted in the clean limit is not observed.

Evidence for Nodal Quasiparticles in the Nonmagnetic SuperconductorYNi2B2Cvia Field-Angle-Dependent Heat Capacity

“…In order to study the elusive angular variation in the low temperature specific heat [18,19], we built a probe specifically designed to look at the DOS variation with field angle. The probe was designed to fit into a Quantum Design Physical Properties Measurement System with a 7 T transverse magnet.…”

Specific heat of underdoped cuprate superconductors from a phenomenological layered Boson–Fermion model

“…The lattice specific heat C l of a cuprate, which is generally considered as not changing with the onset of superconductivity [17], turns out to give a crucial contribution to the total specific heat. Although a series of indirect methods have been used to extract the electronic component of the total specific heat [16,18,19,24], we use the Phonon Density of States (PDOS) directly derived from Angle Resolved Photoemission Spectroscopy (ARPES) experiments to calculate the lattice specific heat as shown in Refs.…”

“…[16] and references therein), and its superconducting counterpart that evolves as γ 0 when the temperature approaches zero. Secondly, there is a quadratic αT 2 term for zero magnetic field [17][18][19] below T c (not exhibited in conventional superconductors), which changes to a H 1/2 T component in the presence of an external magnetic field [20] H, attributable to the superconducting part of the electronic specific heat C es . The reported values for this two constants depend strongly on the conditions of each experiment [17] and on the theoretical method used to relate the different parts of the total specific heat.…”

“…Secondly, there is a quadratic αT 2 term for zero magnetic field [17][18][19] below T c (not exhibited in conventional superconductors), which changes to a H 1/2 T component in the presence of an external magnetic field [20] H, attributable to the superconducting part of the electronic specific heat C es . The reported values for this two constants depend strongly on the conditions of each experiment [17] and on the theoretical method used to relate the different parts of the total specific heat. Thirdly, there is a "jump" in the constant pressure specific heat [21] C p at T c (at zero magnetic field and evolving into a "peak" at finite magnetic field), ∆C p /T c , attributable to the C es component, indicating a second order phase transition which in turn becomes a smooth maximum as doping decreases [22].…”

Magnetic-field dependence of the low-temperature specific heat of the electron-doped superconductorPr1.85Ce0.15CuO4

“…In the inset we replotted γ(H) against H 1/2 , which shows a very good linear relation in the fitting range. By adopting the theoretical form A = γ n ( 8a 2 πHC2 ) 1/2 we obtain γ n = 4.1mJ/molK 2 , if we take the reasonable choices H C2 ≈ 6T and a ≈ 0.7 24 .…”