Relaxation time spectrum of low-energy excitations in one- and two-dimensional materials with charge or spin density waves

TL;DR

This study investigates the thermal relaxation behavior of low-energy excitations in low-dimensional materials with charge or spin density waves at very low temperatures and high magnetic fields, revealing how doping affects relaxation times and ground states.

Contribution

It provides the first detailed analysis of the relaxation time spectrum in these materials, highlighting the influence of magnetic field and doping on low-energy excitations and ground state formation.

Findings

Relaxation time is mainly thermally activated across all materials.

Maximum relaxation time increases with magnetic field strength.

Doping shifts the relaxation spectrum to longer times, indicating SDW ground state formation.

Abstract

The long-time thermal relaxation of (TMTTF)$_2$Br, Sr$_{14}$Cu$_{24}$O$_{41}$ and Sr$_2$Ca$_{12}$Cu$_{24}$O$_{41}$ single crystals at temperatures below 1 K and magnetic field up to 10 T is investigated. The data allow us to determine the relaxation time spectrum of the low energy excitations caused by the charge-density wave (CDW) or spin-density wave (SDW). The relaxation time is mainly determined by a thermal activated process for all investigated materials. The maximum relaxation time increases with increasing magnetic field. The distribution of barrier heights corresponds to one or two Gaussian functions. The doping of Sr$_{14-x}$Ca$_{x}$Cu$_{24}$O$_{41}$ with Ca leads to a drastic shift of the relaxation time spectrum to longer time. The maximum relaxation time changes from 50 s (x = 0) to 3000 s (x = 12) at 0.1 K and 10 T. The observed thermal relaxation at x=12 clearly indicates the formation of the SDW ground state at low temperatures.