Collective excitations in unconventional superconductors

Abstract

ABSTRACT In light of recent experiments study of the collective excitations in unconventional superconductors (USC) becomes very important. We build by path integration technique 2D and 3D models of p- and d-pairing for superfluids and superconductors (SC). Within these models we calculate the collective excitations in different USC (high temperaturesuperconductors (HTSC), heavy fermion superconductors (HFSC) etc.) under p- and d- pairing. We considered both bulkand 2D systems. Some recent ideas concerning realization in HTSC of the mixtures of different states are investigated. Inparticular, we consider the mixture of d22 and states in HTSC. Obtained results could be used for interpretation of the sound and microwave absorption data as well as for identification of the type of pairing and order parameter in unconventional superconductors.Keywords: unconventional superconductors, p- and d-pairing, collective excitations 1. INTRODUCTION Up to now study ofthe collective excitations in USC carries exotic character via a few reasons. First of all while there weresome evidences of nontrivial type of pairing in some superconductors (HFSC, HTSC etc.) there was not superconductor inwhich unconventional pairing has been established exactly.Secondly, there was not found strong evidences ofexisting ofthe collective excitations in superconductors.The situation has changed drastically within last few years removing study of the collective excitations in USC into realplane. In light of recent experiments this topic becomes very important. First of all about a few years ago an amplitudemode (with frequency of order 2A) has been observed in films of ordinary superconductors.Secondly, now the type ofpairing is established for many superconductors.We have s-pairing in ordinary superconductors and electron-type HTSC; p-pairing in pure 3He; 3He in aerogel, SR2RuO4(HTSC), UPt3 (HFSC) and d-pairing in hole-type HTSC, organic superconductors, some HFSC (UPd2A13, CePd2Si2, CeIn3,