Theoretical studies for identifying horizontal line nodes via angle-resolved density-of-states measurements: Application to Sr_2RuO_4

摘要

On the basis of the microscopic quasiclassical Eilenberger theory, we analyze the recent angle-resolved specific heat experiment carried out at low temperature for Sr2RuO4 to identify the superconducting gap symmetry, comprising either horizontal or vertical line nodes relative to the tetragonal crystal symmetry. Several characteristics, in particular, the landscape of the in-plane oscillation amplitude A(4)(B, T) with a definite sign for almost the entire B-T plane are best explained by the horizontal line node symmetry, especially when the multiband and Pauli paramagnetic effects are taken into account. The present analysis of A(4)(B, T) with definite sign points to the presence of an anomalous field region at a lower temperature in the experimental data, whose origin is investigated. Our theory demonstrates the application and uniqueness of the field-rotating thermodynamic measurements in uncovering the precise gap structure for target materials.