Identification of strong and weak interacting two level systems in KBr:CN

TL;DR

This paper investigates the nature of tunneling two-level systems (TLSs) in disordered crystals, specifically KBr:CN, by calculating TLS-phonon couplings to identify strong and weak interacting TLSs, supporting a recent theoretical model.

Contribution

It explicitly calculates TLS-phonon couplings in KBr:CN, supports a recent theory on TLSs, and identifies relevant TLSs in the system for the first time.

Findings

Supports the theory of inversion pairs as TLSs

Identifies relevant TLSs in KBr:CN

Estimates parameters consistent with the theory

Abstract

Tunneling two level systems (TLSs) are believed to be the source of phenomena such as the universal low temperature properties in disordered and amorphous solids, and $1/f$ noise. The existence of these phenomena in a large variety of dissimilar physical systems testifies for the universal nature of the TLSs, which however, is not yet known. Following a recent suggestion that attributes the low temperature TLSs to inversion pairs [M. Schechter and P.C.E. Stamp, arXiv:0910.1283.] we calculate explicitly the TLS-phonon coupling of inversion symmetric and asymmetric TLSs in a given disordered crystal. Our work (a) estimates parameters that support the theory in M. Schechter and P.C.E. Stamp, arXiv:0910.1283, in its general form, and (b) positively identifies, for the first time, the relevant TLSs in a given system.